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Notes and Further Reading

For "THE SPACE BOOK" by Jim Bell (Sterling, 2013)

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I consulted a huge number of resources during the research for this book, including a variety of general historical and encyclopedic sources to verify much of the factual information, and a variety of websites for additional details and follow-up (especially for many of the topics in which there are hot new results or substantial ongoing controversies).

Below I have attempted to document as many of those resources as my notes and memory have allowed, and to direct you to some additional resources where you can find more information on a particular topic. The Internet is dynamic, of course, and so some of the websites pointed to below may have become stale by the time this book appears in print.

Selecting just 250 milestones in the entire history of astronomy and space exploration (past, present, and future) is a daunting task, and my selections naturally reflect my own biases, knowledge, and experience. I would be delighted to consider suggestions for other topics to swap in for future editions of this book, and of course would also welcome any corrections or suggestions in general about the content. Please feel free to e-mail me at, or contact me through my website at

General Reading

Beatty, J. Kelly, Carolyn Collins Petersen, and Andrew Chaikin, eds. The New Solar System. Cambridge, UK: Cambridge University Press, 1998.

Levy, David H., ed. The Scientific American Book of the Cosmos. New York: St. Martin’s Press, 2000.

Mitton, Simon, ed. The Cambridge Encyclopaedia of Astronomy. Cambridge, UK: Cambridge University Press, 2001.

    Moore, Sir Patrick, ed. Astronomy Encyclopedia. Oxford, UK: Oxford University Press, 2002.

Weissman, Paul R., Lucy-Ann McFadden, and Torrance V. Johnson, eds. Encyclopedia of the Solar System. San Diego, CA: Academic Press, 1999.

General-Interest Websites

    Curious about Astronomy? Ask an Astronomer:

    Nine Planets:

    Views of the Solar System:

    Bad Astronomy (blog):



Notes on Specific Entries in the Book

c. 13.7 Billion bce, Big Bang

Two outstanding introductory articles about the big bang are “Misconceptions about the Big Bang” by C. Lineweaver and T. Davis (Scientific American, February 2005) and “The First Few Microseconds” by M. Riordan and W. Zajc (Scientific American, April 2006).

c. 13.5 Billion bce, Recombination Era

Using data from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, cosmologists have been able to date the start of the recombination era to the stunningly accurate level of 380,000 years after the big bang. WMAP results were subsequently named Science magazine’s “breakthrough of the year” for 2003 (see Science, December 19, 2003).

c. 13.5 Billion bce, First Stars

Cosmologist Volker Bromm and his colleagues at the University of Texas at Austin host a wonderful website with tutorials, papers, and computer animations about their work on understanding the universe’s first stars and galaxies:….

c. 13.3 Billion bce, Milky Way

A very nice series of maps and photographs of the Milky Way can be found online at the Atlas of the Universe website:

c. 5 Billion bce, Solar Nebula

The generally accepted father of the modern solar nebular disk model is the Soviet astronomer Victor Safronov (1917–1999); his book Evolution of the Protoplanetary Cloud and the Formation of the Earth and the Planets (published by Israel Program for Scientific Translations for NASA and the National Science Foundation, NASA Technical Translation F-677, 1972) is a classic text in the field.

c. 4.6 Billion bce, Violent Proto-Sun

The Australia Telescope Outreach and Education website has a great illustrated primer on the formation and evolution of protostars:….

c. 4.6 Billion bce, Birth of the Sun

Spectacular photos, movies, and other information about the Sun can be found online at the website for the ESA/NASA Solar and Heliospheric Observatory (SOHO) satellite:

c. 4.5 Billion bce, Mercury

An enjoyable account of the history and science of the planet Mercury prior to the MESSENGER mission can be found in Mercury: The Elusive Planet, by Robert G. Strom (Cambridge, UK: Cambridge University Press, 1987).

c. 4.5 Billion bce, Venus

The Nine Planets website is an outstanding place to start learning more about all the planets, moons, and small bodies in our solar system. Check out their “Venus” page at

c. 4.5 Billion bce, Earth

Geologist G. Brent Dalrymple’s book The Age of the Earth (Stanford, CA: Stanford University Press, 1994) is an outstanding and authoritative source for understanding how we know that our planet is billions of years old.

c. 4.5 Billion bce, Mars

The Planetary Society, the world’s largest public space-advocacy organization, hosts an informative set of Web pages devoted to the exploration of Mars:

c. 4.5 Billion bce, Main Asteroid Belt

Details about the discoveries, orbits, and other parameters of more than a half million minor planets in the main asteroid belt, near-Earth space, and elsewhere in the solar system are compiled online by the International Astronomical Union’s Minor Planet Center at

c. 4.5 Billion bce, Jupiter

An authoritative recent scientific summary of almost everything we know about Jupiter can be found in Jupiter: The Planet, Satellites, and Magnetosphere, edited by Fran Bagenal, Timothy E. Dowling, and William B. McKinnon (New York: Cambridge University Press, 2007).

c. 4.5 Billion bce, Saturn

Saturn’s atmosphere is less dynamic than Jupiter’s, but it still reveals interesting and enigmatic features, such as a strange hexagonal cloud pattern surrounding the north pole ( and a bright new storm system that became visible in 2010, even with amateur telescopes, and is being studied by the Cassini spacecraft (

c. 4.5 Billion bce, Uranus

A wonderful collection of photos of the Uranian atmosphere, rings, and moons can be found on the NASA/Caltech Jet Propulsion Laboratory’s Planetary Photojournal site for Uranus, at

c. 4.5 Billion bce, Neptune

Understanding the formation of ice giants such as Neptune and Uranus is a hot topic in modern planetary science. The idea that these and other planets have migrated outward since their formation is often known as the Nice model, after the Nice Observatory in France, where many of the model’s proponents work (see, for example, “The Chaotic Genesis of Planets,” by Douglas N. C. Lin, Scientific American, May 2008).

c. 4.5 Billion bce, Pluto and the Kuiper Belt

The fun 365 Days of Astronomy podcast site has an interesting entry on the Kuiper (rhymes with “viper”) belt online at….

c. 4.5 Billion bce, Birth of the Moon

The University of Arizona Space Science Series book The Origin of the Earth and Moon, edited by Robin M. Canup and Kevin Righter (Tucson: University of Arizona Press, 2000), contains a comprehensive summary of the history and science of the giant impact model and other hypotheses for the Moon’s formation.

c. 4.1 Billion bce, Late Heavy Bombardment

The giant planets likely played a significant role in causing the late heavy bombardment: see for a readable summary and links.

c. 3.8 Billion bce, Life on Earth

For a great summary of some of the latest research on the beginnings of life on our planet, see “The Origin of Life on Earth,” by Alonso Ricardo and Jack W. Szostak, Scientific American, September 2009.

550 Million bce, Cambrian Explosion

Douglas H. Erwin’s Extinction: How Life on Earth Nearly Ended 250 Million Years Ago (Princeton, NJ: Princeton University Press, 2006) gives a comprehensive and entertaining summary of the Permian-Triassic extinction event.

65 Million bce, Dinosaur-Killing Impact

For more details and references about the controversy surrounding the impact hypothesis for the extinction of the dinosaurs 65 million years ago, as well as the causes of other extinction events, a great place to start is Wikipedia’s K-T extinction event page at

200,000 bce, Homo Sapiens

Seed magazine reporter Holly Capelo wrote an interesting summary of recent evidence that Paleolithic cave art may indeed capture some aspects of ancient astronomical and celestial lore. See for details.

c. 50,000 bce, Arizona Impact

Geologist David Rajmon has compiled an online database of the nearly two hundred known and suspected impact-crater sites on the Earth:

c. 5000 bce, Birth of Cosmology

According to an official NASA definition, cosmology is the study of the structure and changes in the present universe, whereas the study of the origin and evolution of the early universe is technically called cosmogony (although no one I know uses the word cosmogony).

c. 3000 bce, Ancient Observatories

Cecil A. Newham’s The Astronomical Significance of Stonehenge (Warminster, UK: Coates & Parker, 1993) provides a fascinating scientific analysis of that ancient and mysterious structure.

c. 2500 bce, Egyptian Astronomy

I remember reading an early edition of Edwin C. Krupp’s Echoes of the Ancient Skies: The Astronomy of Lost Civilizations (Mineola, NY: Dover, 2003) when I was young and being fascinated by how much the objects and motions of the sky meant to our distant ancestors.

c. 2100 bce, Astronomy in China

University of Maine professor Marilyn Shea hosts an excellent illustrated and annotated website highlighting many ancient Chinese astronomers and astronomical instruments:

c. 500 bce, Earth Is Round!

In case Pythagoras, Eratosthenes, and the modern space program have not convinced you that you’re living on a rotating sphere, you can always stick your head in the sand and join other nonbelievers from the Flat Earth Society by visiting

c. 400 bce, Greek Geocentrism

According to Bakersfield College astronomy professor Nick Strobel, who reviews some aspects of Greek cosmology on his website (, Aristotle “had probably the most significant influence on many fields of studies (science, theology, philosophy, etc.) of any single person in history.”

c. 400 bce, Western Astrology

Astronomy professor Andrew Fraknoi, of Foothill College (Los Altos Hills, California) and the Astronomical Society of the Pacific, has an excellent collection of pointers and resources for those who want to skeptically examine or debunk astronomy-related pseudoscience such as astrology. Check it out at

c. 280 bce, Sun-Centered Cosmos

To really dive into the details of the rich history of cosmology, check out Helge S. Kragh’s Conceptions of Cosmos—From Myths to the Accelerating Universe: A History of Cosmology (New York: Oxford University Press, 2007).

c. 250 bce, Eratosthenes Measures the Earth

Since 2000, an international program for teachers and students called Follow the Path of Eratosthenes has enabled students to reproduce Eratosthenes’s more than 2,200-year-old experiment on their own. Find out how to join in at

c. 150 bce, Stellar Magnitude

Still confused about the backward stellar magnitude system used by astronomers? Sky & Telescope magazine contributor Alan MacRobert’s online article at… might help.

c. 100 bce, First Computer

Two excellent review articles provide much more detail on the history and decoding of the Antikythera mechanism: Derek J. de Solla Price’s “An Ancient Greek Computer” (Scientific American, June 1959, pp. 60–67) and Tony Freeth’s “Decoding an Ancient Computer” (Scientific American, December 2009, pp. 76–83).

45 bce, Julian Calendar

A wonderful introduction to the early Roman calendar can be found on the WebExhibits online museum site:

c. 150 Ptolemy’s Almagest

Physics professor Dennis Duke of Florida State University has put together an educational—and entertaining—set of Web-based animations that graphically display the nature of circular planetary motions according to the Ptolemaic/Almagest model. See “Ancient Planetary Model Animations” ( for his introduction and outline.

185, Chinese Observe “Guest Star”

A recent NASA press release at describes how astronomers, using NASA’s Spitzer Space Telescope and the Wide-Field Infrared Survey Explorer satellite (WISE), have been able to piece together the details of the supernova of 185 to explain its progression from the bright flash first observed by Chinese astronomers to the roughly spherical remnants of gas and dust that are visible today.

c. 500, Aryabhatiya

Walter E. Clark’s 1930 English translation of the Aryabhatiya of Aryabhata is available free online, at

c. 700, Finding Easter

You can check Venerable Bede’s calculations of the date of Easter using modern computus methods with the help of the Astronomical Society of South Australia’s website:

c. 825, Early Arabic Astronomy

A useful and educational introductory reference on early Arabic astronomy is Owen Gingerich’s “Islamic Astronomy” (Scientific American, April 1986).

c. 964, Andromeda Sighted

Tenth-century Persian astronomer ‘Abd al-Rahmān al-Sūfī’s The Book of the Fixed Stars is available online at the World Digital Library website:

c. 1000, Experimental Astrophysics

More details about the lives and work of al-Haytham and al-Bīrūnī can be found in recent online articles by Jim Al-Khalili, professor of theoretical physics at the University of Surrey (, and author Richard Covington (…).

c. 1000, Mayan Astronomy

A high-resolution version of the complete Dresden Codex can be downloaded from See also Colgate University professor Anthony Aveni’s Conversing with the Planets: How Science and Myth Invented the Cosmos (New York: Kodansha International, 1994).

1054, “Daytime Star” Observed

An entertaining historical and scientific description of the daytime star of 1054, and its resulting supernova remnant, can be found in Simon Mitton’s The Crab Nebula (New York: Charles Scribner’s Sons, 1979).

c. 1230, De Sphaera

You can learn a lot more about the history, accomplishments, and writings of John of Sacrobosco from Swansea University professor Adam Mosley’s websites, starting at

c. 1260, Large Medieval Observatories

NASA maintains an illustrated and informative website on ancient (and modern) astronomical observatories—Ancient Observatories, Timeless Knowledge—at

c. 1500, Early Calculus

The figure is adapted from K. Ramasubramanian, M. D. Srinivas, and M. S. Sriram, “Modification of the Earlier Indian Planetary Theory by the Kerala Astronomers (c. 1500 ad) and the Implied Heliocentric Picture of Planetary Motion” (Current Science 66, no. 4 [May 25, 1994], pp. 784–790).

1543, Copernicus’s De Revolutionibus

Al Van Helden from Rice University’s Galileo Project wrote an outstanding summary of the history of the Copernican system, which is available online at

1572, Brahe’s “Nova Stella”

A great place to start learning more about the fascinating, complex character that was Tycho Brahe is by reading Victor E. Thoren’s The Lord of Uraniborg: A Biography of Tycho Brahe (New York: Cambridge University Press, 1990).

1582, Gregorian Calendar

The US Naval Observatory’s “Introduction to Calendars” Web page provides an interesting summary of the six principal calendar systems currently in worldwide use:…

1596, Mira Variables

An article by Dorrit Hoffleit about the discovery of Mira and its variability can be found on the American Association of Variable Star Observers website at

1600, Bruno’s On the Infinite Universe and Worlds

Wikipedia’s “Giordano Bruno” page ( provides a comprehensive starting point for a more detailed study of the controversial friar, philosopher, and astronomer.

1608, First Astronomical Telescopes

The American Academy of Ophthalmology has an online history of spectacles at; also see “The Telescope” Web page from the Rice University Galileo Project:

1610, Galileo’s Starry Messenger

The Italian Museo Galileo: Institute and Museum of the History of Science in Florence has a wonderful online exhibit with information and details about Galileo’s telescope at For fascinating and more personal revelations about Galileo the man, see also Dava Sobel’s wonderful Galileo’s Daughter: A Historical Memoir of Science, Faith, and Love (New York: Walker & Company, 2011).

1610, Io

The most comprehensive recent scientific summaries of what we now know about Io can be found in Io After Galileo: A New View of Jupiter’s Volcanic Moon, edited by Rosaly M. C. Lopes and John R. Spencer (Chichester, UK: Springer/Praxis, 2006).

1610, Europa

Spectacular views of Europa from the Voyager and Galileo probes can be found on the NASA Planetary Photojournal search page at

1610, Ganymede

For more of the history of orbital resonances and celestial dynamics, including a glimpse into some of the daunting math at the cutting edge of that field, see Carl D. Murray and Stanley F. Dermott’s Solar System Dynamics (New York: Cambridge University Press, 2000).

1610, Callisto

Visit Lunar and Planetary Institute planetary scientist Dr. Paul Schenk’s 3D House of Satellites blog at… to learn more about what Callisto and the other Galilean moons are like up close.

1610, Orion Nebula “Discovered”

To learn more about our distant ancestors’ ideas about the Orion Nebula, check out Edward C. Krupp’s article “Igniting the Hearth,” in the February 1999 issue of Sky & Telescope (vol. 97, no. 2).

1619, Three Laws of Planetary Motion

Fascinating background and details about Johannes Kepler and his work can be found in Curtis Wilson’s “How Did Kepler Discover His First Two Laws?” (Scientific American, March 1972) and Owen Gingerich’s The Great Copernicus Chase and Other Adventures in Astronomical History (Cambridge, MA: Sky Publishing, 1992).

1639, Venus Transits the Sun

A great popular-level account of the history of Venus transit observations is in William Sheehan and John Westfall’s The Transits of Venus (Amherst, NY: Prometheus, 2004).

1650, Mizar-Alcor Sextuple System

Noted stellar astronomer James Kaler hosts a website with lots of details about named stars such as Mizar and Alcor at; see also Leos Ondra’s article “A New View of Mizar,” originally published in Sky & Telescope (July 2004), and available online at the author’s website:

1655, Titan

Huygens’s treatise on Saturn, Systema Saturnium, is available online from the Smithsonian Institution Libraries at

1659, Saturn Has Rings

An enormous amount of information, including images and movies, can be found on the NASA Planetary Data System’s “Saturn’s Rings” Web page at; see also the previous note.

1665, Great Red Spot

Check out Andrew P. Ingersoll’s review of what we know about the Great Red Spot in “Atmospheres of the Giant Planets,” chapter 15 in The New Solar System, edited by J. Kelly Beatty, Carolyn Collins Petersen, and Andrew Chaikin (Cambridge, MA: Sky Publishing, 1999).

1665, Globular Clusters

The National Optical Astronomy Observatories keeps a wonderful website with photos and other information about globular clusters and other astronomical objects at

1671, Iapetus

Additional images and details about Iapetus can be found on the Cassini mission’s “Iapetus” Web page:

1672, Rhea

Initial details about the possible halo and ring system around Rhea were published by G. H. Jones, et al., in “The Dust Halo of Saturn’s Largest Icy Moon, Rhea” (Science 319, no. 5868 [March 7, 2008], pp. 1380–1384).

1676, Speed of Light

See also Steven Soter and Neil deGrasse Tyson (eds.), Cosmic Horizons: Astronomy at the Cutting Edge (New York: New Press, 2001).

1682, Halley’s Comet

For historical background, see Alan H. Cook’s Edmond Halley: Charting the Heavens and the Seas (New York: Clarendon Press, 1998). Lists and orbital data for all known periodic comets are compiled by the International Astronomical Union’s Minor Planet Center at

1684, Tethys

An animation of the surface geology of Tethys was generated from Voyager images by Calvin J. Hamilton and can be found online at

1684, Dione

Hundreds of images of Dione, alone and with other moons and rings of Saturn, can be found on the NASA Planetary Photojournal’s feature search page at

1684, Zodiacal Light

Additional details of the early history of zodiacal light observations can be found in C. E. Brame’s “The Zodiacal Light” (Popular Science Monthly 11 [July 1877]); it’s available online at….

1686, Origin of Tides

Excellent introductory physics-level discussions of tides (including common misconceptions about their origin) can be found at “How Tides Work” on Ethan Siegel’s blog Starts with a Bang! ( and “Tidal Misconceptions,” by Donald Simanek (, as well as pages 265–274 in Vernon D. Barger and Martin G. Olsson’s Classical Mechanics: A Modern Perspective (New York: McGraw-Hill, 1973).

1687, Newton’s Laws of Gravity and Motion

A wonderful source for understanding Newton’s work in its historical context is On the Shoulders of Giants: The Great Works of Physics and Astronomy, edited, with commentary, by Stephen Hawking (Philadelphia: Running Press, 2002).

1718, Proper Motion of Stars

An accessible historical accounting of Halley’s “Considerations on the Changes of the Latitudes of Some of the Principal Fixed Stars (1718)” can be found in Robert G. Aitken’s “Edmund [sic] Halley and Stellar Proper Motions” (Astronomical Society of the Pacific Leaflets 4, no. 164 [October 1942], pp. 103–112); it is available online at….

1757, Celestial Navigation

The bible of seagoing navigation and instrumentation is widely regarded to be Nathaniel Bowditch’s The American Practical Navigator, first published in 1802 and available online through several sources, including

1764, Planetary Nebulae

Details on Hubble Space Telescope images of the Cat’s Eye and other planetary nebulae can be found online at

1771, Messier Catalog

Various compilations and links to “Messier marathon” sites can be found via the Paris Observatory at, and from the Students for the Exploration and Development of Space (SEDS) at Also, an English translation of Messier’s original 1771 catalog of the first 45 objects is online at

1772, Lagrange Points

Astrophysicist and science popularizer Neil deGrasse Tyson has an entertaining and educational essay about the history, physics, and space exploration potential of Lagrange points at….

1781, Discovery of Uranus

Author Michael Lemonick’s The Georgian Star: How William and Caroline Herschel Revolutionized Our Understanding of the Cosmos (New York: W.W. Norton, 2009) provides a detailed summary and tribute to both Herschels’ lasting contributions to eighteenth-century astronomy.

1787, Titania

A fascinating first-person account of the discovery of the first two moons of Uranus was published by William Herschel in 1787 as “An Account of the Discovery of Two Satellites Revolving Round the Georgian Planet,” in Philosophical Transactions of the Royal Society 77 (January 1, 1787, pp. 125–129), and is freely available online at…. (Just remember that ftar = star, fatellite = satellite, and so on.)

1787, Oberon

William Herschel’s son, John, wrote a short summary in 1834 of the then-known details of the orbits of Oberon and Titania and the obliquity of Uranus called “On the Satellites of Uranus,” published in the Monthly Notices of the Royal Astronomical Society (3, no. 5 [March 14, 1834], pp. 35–36), and available online at….

1789, Enceladus

A 2006 press release about the watery plumes of Enceladus, called “Cassini Images of Enceladus Suggest Geysers Erupt Liquid Water at the Moon’s South Pole,” with links and pointers to more images and other information, can be found online at the Cassini Imaging Central Laboratory for Operations:

1789, Mimas

An interesting account of some of the details in the design and fabrication of the mirrors for Herschel’s 40-foot (12-meter) telescope can be found in W. H. Steavenson’s “Herschel’s First 40-foot Speculum,” published in The Observatory (50 [1927], pp. 114–118) and available online at

1794, Meteorites Come from Space

A wonderful recent introduction to the history and science of meteorites appears in Meteorites, by Caroline Smith, Sara Russell, and Gretchen Benedix (Buffalo, NY: Firefly Books, 2011).

1795, Encke’s Comet

J. Donald Fernie published an entertaining summary of Caroline Herschel’s life and achievements, “The Inimitable Caroline,” in the November/December 2007 issue of American Scientist (vol. 95, no. 6), available online at

1801, Discovery of Ceres

A nice collection of Hubble Space Telescope photos and links for images of both 1 Ceres and 4 Vesta can be found on astronomy professor Courtney Seligman’s website:

1807, Discovery of Vesta

An excellent recent scientific summary of asteroid research appears in the 2002 book Asteroids III (Tucson: University of Arizona Press, 2002), edited by William F. Bottke and colleagues; it is available online at and includes an entire chapter by University of Hawaii Professor Klaus Keil entitled “Geological History of Asteroid 4 Vesta: The Smallest Terrestrial Planet” (pp. 573–584).

1814, Birth of Spectroscopy

The Fraunhofer Society, a group of German research institutes devoted to cutting-edge applied scientific research, has an online biography of Joseph von Fraunhofer’s life and achievements at

1838, Stellar Parallax

The photo on page 000 is a screen shot from a wonderful Web application by Vladimir Bodurov that lets you view the stars in the Sun’s neighborhood from any direction. See

1839, First Astrophotographs

John Draper and his son Henry lived and worked in Hastings-on-Hudson, New York. The Hastings Historical society has some interesting detailed background about the astronomical photography work of the Drapers of Hastings posted online at… and….

1846, Discovery of Neptune

The prolific and learned British astronomer Sir Patrick Moore has written an entertaining and engaging history of the discovery of Neptune in The Planet Neptune: An Historical Survey Before Voyager (New York: Wiley, 1996).

1846, Triton

For a modern summary of Triton’s composition, geology, and possible origin, see D. Cruikshank, “Triton, Pluto, Centaurs, and Trans-Neptunian Bodies,” in T. Encrenaz, R. Kallenbach, T. Owen, and C. Sotin, The Outer Planets and Their Moons (Norwell, MA: Springer, 2005, pp. 421–440).

1847, Miss Mitchell’s Comet

More information about Maria Mitchell’s life and legacy can be found on the website of the Maria Mitchell Association (, “founded in 1902 to preserve the legacy of Nantucket native astronomer, naturalist, librarian, and, above all, educator.”

1848, Doppler Shift of Light

UCLA astronomy professor Ned Wright has an excellent online tutorial about Doppler shifts and cosmology at

1848, Hyperion

More details about the strange landforms and internal structure of Hyperion can be found in P. C. Thomas, et al., “Hyperion’s Sponge-like Appearance” (Nature 448, no. 7149 [2007], pp. 50–56).

1851, Foucault’s Pendulum

For more details and background about the theory and operation of Foucault’s pendulum, see the California Academy of Science’s excellent online tutorial at

1851, Ariel and Umbriel

A detailed account of the life and history of the skilled and prolific observational astronomer William Lassell can be found in his 1880 obituary, written by Margaret Huggins, in The Observatory (vol. 3 [1880], pp. 586–590), available online at….

1857, Kirkwood Gaps

Interesting additional details about Kirkwood’s life and discoveries can be found in J. Donald Fernie, “The American Kepler” (New Scientist 87, September/October 1999, p. 398), online at

1859, Solar Flares

More details and background about Carrington’s 1859 solar flare event is featured in the May 6, 2008, “NASA Science News: A Super Solar Flare” feature posted online at….

1859, Search for Vulcan

The search is chronicled in detail in Robert Fontenrose’s article “In Search of Vulcan” (Journal for the History of Astronomy 4 [1973], p. 145), available online at….

1862, White Dwarfs

An outstanding account of the history and legacy of telescope makers Alvan Clark and Sons can be found in Deborah Jean Warner and Robert B. Ariail’s Alvan Clark & Sons: Artists in Optics (Richmond, VA: Willmann-Bell, 1995).

1866, Source of the Leonid Meteors

A great source of information and details about the Leonids and other meteor showers can be found at author and amateur astronomer Gary Kronk’s website:

1868, Helium

The Wikipedia entry on helium at contains extensive details and references about this cosmically important element.

1877, Deimos and Phobos

A personal account of Asaph Hall’s discovery of the moons of Mars can be found in “The Discovery of the Satellites of Mars” (Monthly Notices of the Royal Astronomical Society 38, [February 8, 1878], pp. 205–209); it’s available online at Also, details about the Mars rovers’ observations of the solar transits of both moons can be found in a scientific article that I and a number of colleagues wrote called “Solar Eclipses of Phobos and Deimos Observed from the Surface of Mars” (Nature 436 [July 7, 2005], pp. 55–57).

1887, End of the Ether

It’s fascinating to read Michelson and Morley’s original paper describing their experiment and results. It was published in 1887 as “On the Relative Motion of the Earth and the Luminiferous Ether” in the American Journal of Science (34, no. 203 [November 1887], pp. 333–345), and is available free from the American Institute of Physics at

1892, Amalthea

Barnard’s description of his discovery was published in “Discovery and Observations of a Fifth Satellite to Jupiter” (Astronomical Journal 12 [1892], pp. 81–85), which can be read online at….

1893, Star Color = Star Temperature

Wilhelm Wien won the Nobel Prize in Physics in 1911 for his discoveries in light and energy; for a list of all past winners of the physics prize, see

1895, Milky Way Dark Lanes

A summary of Max Wolf’s astronomical career can be found in Joseph S. Tenn’s “Max Wolf: The Twenty-Fifth Bruce Medalist” (Mercury 23 [July–August 1994], pp. 27–28); it’s available online at

1896, Greenhouse Effect

A detailed modern discussion of the greenhouse effect can be found in the United Nations’ Intergovernmental Panel on Climate Change Fourth Assessment Report’s Frequently Asked Question 1.3 (pp. 115–116), “What is the Greenhouse Effect?” in chapter 1, “Historical Overview of Climate Change Science,” available online at

1896, Radioactivity

An outstanding and detailed, readable summary of the principles and history of radioactivity and radioactive dating can be found in planetary scientist Matthew Hedman’s The Age of Everything: How Science Explores the Past (Chicago: University of Chicago Press, 2007).

1898–1899, Discovery of Phoebe

Additional images and details about Phoebe can be found on the Cassini mission’s “Phoebe” Web page:

1900, Quantum Mechanics

A series of introductory to mind-bending articles about quantum mechanics and the quantum world is available online from New Scientist magazine, at

1901, Pickering’s “Harvard Computers”

An article by Sue Nelson in the September 4, 2008, issue of Nature magazine provides fascinating additional history and details about the work of Pickering’s “Harvard Computers”: see Nature 455 (September 4, 2008): pp. 36–37.

1904, Himalia

Animated orbital views of the irregular satellites of all of the giant planets can be seen with the University of Maryland’s online Solar System Visualizer, at

1905, Einstein’s “Miracle Year”

Wikipedia’s exhaustive entry on the life and career of Albert Einstein at is an outstanding place to begin to learn more about the iconic physicist whom Time magazine dubbed “Person of the Century” for 1900–1999.

1906, Jupiter’s Trojan Asteroids

Saturn, Neptune, and Mars (but, curiously, not Uranus) have also been found to have Trojan asteroids at their leading and trailing L4 and L5 points; even the moons Tethys and Dione have been found to have small Trojan satellites in their L4 and L5 points relative to Saturn; for details, see

1906, Mars and Its Canals

Lowell’s Mars and Its Canals, including good renderings of his original hand-drawn maps and globes of Mars, is available online through Google Books via

1908, Tunguska Explosion

Artist and planetary scientist William K. Hartmann of the Planetary Science Institute in Tucson, Arizona, has put together a fascinating account of eyewitness stories and artistic impressions about the Tunguska event at

1908, Cepheid Variables

A lovely biography of Henrietta Swan Leavitt was written by George Johnson: Miss Leavitt’s Stars: The Untold Story of the Woman Who Discovered How to Measure the Universe (New York: W. W. Norton, 2005).

1910, Main Sequence

McGraw-Hill publishers has a fun online applet, “Stellar Evolution and the H-R Diagram,” that can be used to track the evolution of stars of different mass along and eventually off the main sequence:

1918, Size of the Milky Way

Interesting reviews and details about the 1920 “Great Debate” between Harlow Shapley and his fellow American astronomer Heber Curtis (1872–1942) about the size of the universe can be found at

1920, “Centaur” Asteroids

An up-to-date list of all known Centaurs and other “scattered-disk objects,” as they are sometimes known, is compiled by the International Astronomical Union’s Minor Planet Center at

1924, Eddington’s Mass-Luminosity Relation

Arthur Eddington’s 1926 book, The Internal Constitution of the Stars (Cambridge, UK: Cambridge University Press), became an instant astronomy classroom staple as well as an influential inspiration for generations of astrophysicists.

1926, Liquid-Fueled Rocketry

Goddard’s original 1919 book on rocketry, A Method to Reach Extreme Altitudes (Washington, D.C.: Smithsonian Institution Press), can be downloaded for free from

1927, The Milky Way Rotates

UCLA astronomer Andrea Ghez’s Galactic Center Group hosts a wonderfully illustrated summary of views of the center of our galaxy at different wavelengths at

1929, Hubble’s Law

For an illuminating account of the story behind Hubble’s law, check out Donald E. Osterbrock, Joel A. Gwinn, and Ronald S. Brashear’s article “Edwin Hubble and the Expanding Universe,” in Scientific American (269 [July 1993], pp. 84–89).

1930, Discovery of Pluto

The backstory and details about Lowell Observatory astronomer Clyde Tombaugh’s search for and discovery of Pluto can be found in his article “The Search for the Ninth Planet, Pluto,” in the Astronomical Society of the Pacific Leaflets 5, no. 209 (July 1946), pp. 73–80; it’s online at….

1931, Radio Astronomy

Karl Jansky’s brother Cyril, Jr.’s, 1956 tale of the early history of Karl’s discovery of “electrical disturbances apparently of extraterrestrial origin” is posted online as “My Brother Karl Jansky and His Discovery of Radio Waves from Beyond the Earth” at the Ohio State University’s Big Ear Radio Observatory website:

1932, Öpik-Oort Cloud

Jan Oort’s 1950 Bulletin of the Astronomical Institutes of the Netherlands article, from which the Oort Cloud gets its name, expands on Ernst Öpik’s original 1932 hypothesis and is freely available online at….

1933, Neutron Stars

Details about the Hubble Space Telescope’s 1997 visible light identification of a lone neutron star, “Hubble Sees a Neutron Star Alone in Space,” can be found at….

1933, Dark Matter

Neil deGrasse Tyson and Steven Soter provide some more details about the brilliant astronomer and “irascible character” Fritz Zwicky in their profile at…, which is excerpted from Cosmic Horizons: Astronomy at the Cutting Edge (New York: New Press, 2001).

1936, Elliptical Galaxies

Edwin Hubble’s 1936 book, The Realm of the Nebulae (New Haven, CT: Yale University Press), is based on a series of lectures that he gave at Yale in 1935 describing his observations and interpretations of “island universes”—other galaxies separate from our own. The book is now considered a classic in the history of astronomy.

1939, Nuclear Fusion

In his essay on the history of stellar nuclear fusion, “How the Sun Shines” (published online at, astronomer John Bahcall wrote of Hans Bethe’s 1939 paper Energy Production in Stars, “If you are a physicist and only have time to read one paper in the subject, this is the paper to read.”

1945, Geosynchronous Satellites

Arthur C. Clarke’s 1945 prophetic Wireless World magazine article about the future of communications satellites, as well as many other influential early articles and documents about the early space program, can be found in a volume edited by space historian John Logsdon called Exploring the Unknown: Selected Documents in the History of the U.S. Civil Space Program. It’s available online at

1948, Miranda

My planetary science colleague Paul Schenk from the Lunar and Planetary Institute has created some spectacular movies and views of the dramatic and weird topography on tiny Miranda, posted online at

1955, Jupiter’s Magnetic Field

For more details about the 1955 discovery of Jupiter’s magnetic field, see Dr. Leonard Garcia’s article on the Radio Jove website:

1956, Neutrino Astronomy

A great recent review and summary of neutrino astronomy can be found in Graciela B. Gelmini, Alexander Kusenko, and Thomas J. Weile’s “Through Neutrino Eyes: Ghostly Particles Become Astronomical Tools,” in the May 2010 issue of Scientific American.

1957, Sputnik 1

For an entertaining and illuminating glimpse of the America that was shocked by Sputnik and then spurred on to reach the Moon, check out Homer Hickam’s 1998 book, Rocket Boys (New York: Delacorte Press), and the related 1999 film October Sky (Universal Pictures).

1958, Earth’s Radiation Belts

A summary and links to more details about the phenomenally successful Explorer small satellite program (with 93 launches between 1958 and 2012) can be found on Wikipedia at

1958, NASA and the Deep Space Network

The DSN’s official website is For a list of current (as well as past and future) NASA space science missions being tracked by the DSN, see

1959, Far Side of the Moon

The far side of the Moon is not (usually) the same as the dark side. The Moon goes through a cycle of day and night, so, just as they do on Earth, the lit side and the dark side are constantly changing. Only at full Moon is the far side also the dark side; at new Moon, the near side becomes the dark side. Confused? Check out Phil Plait’s explanation and details at his wonderful Bad Astronomy website:

1959, Spiral Galaxies

Spiral galaxy and dark matter researcher Vera Rubin, from the Carnegie Institution of Washington, is one of the key women in the history of astronomy who is profiled in the Astronomical Society of the Pacific’s online Women in Astronomy website:

1960, SETI

A modern perspective on 50 years of SETI can be found in the essay called “An Alien Concept,” by Slate columnist Fred Kaplan in the September 17, 2009, issue of Nature (461, pp. 345–346).

1961, First Humans in Space

In honor of Yuri Gagarin’s status as the first person to travel into space, every April 12 since 2001 has been celebrated as “Yuri’s Night” at space-related parties and events around the world. Find out more about the next Yuri’s Night at

1963, Arecibo Radio Telescope

More information and details about the Arecibo telescope, including a full list of its scientific accomplishments, can be found online at

1963, Quasars

An introduction to Hubble Space Telescope imaging and spectroscopy of quasars and their host galaxies can be found in the online article “Hubble Surveys the ‘Homes’ of Quasars” at

1964, Cosmic Microwave Background

Since its founding in 1925, Bell Laboratories has been a great example of private industry promoting scientific and technological advancement. In addition to the discovery of the cosmic microwave background radiation and the invention of radio astronomy (see page 000), Bell Labs also pioneered the transistor, the laser, solar cells, and the first telecommunications satellite.

1965, Black Holes

An entertaining and educational account of the science and mystery of black holes can be found in astrophysicist Neil deGrasse Tyson’s book Death by Black Hole: And Other Cosmic Quandaries (New York: W. W. Norton, 2007).

1965, Hawking’s “Extreme Physics”

Hawking’s best-selling A Brief History of Time: From the Big Bang to Black Holes (1988) and The Universe in a Nutshell (2001), both published by Bantam Books, are excellent general-audience introductions to modern cosmology and the exotic, nonintuitive world of black holes, singularities, wormholes, and other extreme physics.

1965, Microwave Astronomy

Stanford University’s Gravity Probe B mission website provides some good additional technical detail and links about astrophysical masers at

1966, Venera 3 Reaches Venus

Space history researcher Donald P. Mitchell has created an excellent online summary of the Soviet Union’s 1961–1985 Venera Venus exploration program at

1967, Pulsars

A cartoon animation of a rotating pulsar can be found at the Max Planck Institute for Gravitational Physics Einstein Online website’s “Neutron Stars and Pulsars” page:

1967, Study of Extremophiles

Thomas Brock’s call for expanding the search for habitable environments on the Earth was published in “Life at High Temperatures” (Science 158, no. 3804 [November 1967], pp. 1012–1019).

1969, First on the Moon

An authoritative and entertaining source of moment-by-moment details of Apollo 11 and the other human missions to the Moon is the Apollo Lunar Surface Journal website, edited by Eric M. Jones and Ken Glover, and posted online at

1969, Second on the Moon

Huge numbers of books, movies, and websites have been created to chronicle the history of the Apollo program, but much less has been published about the Soviet Union’s failed human lunar exploration program. An excellent general-level summary of the Soviet efforts, “The Soviet Manned Lunar Program,” is available from the Finnish space-history researcher Marcus Lindroos at

1969, Astronomy Goes Digital

Willard Boyle and George Smith shared a part of the 2009 Nobel Prize in Physics for their invention of the CCD. You can see and hear more details about their pioneering work in their Nobel award lectures, posted online at

1970, Organic Molecules in Murchison Meteorite

A good article with more details about the amino acids discovered in the Murchison meteorite was written by Anne M. Rosenthal for the February 12, 2003, online issue of Astrobiology magazine. “Murchison’s Amino Acids: Tainted Evidence?” is posted at….

1970, Venera 7 Lands on Venus

The National Space Science Data Center maintains a chronological list of Venus space exploration missions, with links to photographs and descriptions of the spacecraft and instruments, at

1970, Lunar Robotic Sample Return

The NASA Lunar Reconnaissance Orbiter Camera team, based at Arizona State University in Tempe, has made a priority of taking photos of “anthropogenic targets” such as the Luna, Surveyor, and Apollo landers; the images and details are posted online at….

1971, Fra Mauro Formation

For fascinating stories and details about all of the Apollo missions, science journalist and space historian Andy Chaiken’s book A Man on the Moon: The Voyages of the Apollo Astronauts (New York: Penguin, 1998) is an outstanding read.

1971, First Mars Orbiters

Planetary scientists William K. Hartmann and Odell Raper’s book The New Mars: The Discoveries of Mariner 9 (NASA Special Publication 337 [Washington, D.C.: NASA Scientific and Technical Information Office, 1974]) is a great way to check out the highlights from the mission of the first Mars orbiter.

1971, Roving on the Moon

Detailed historical documents and technical schematics about the Apollo lunar roving vehicles can be found in A Brief History of the Lunar Roving Vehicle from the NASA Marshall Space Flight Center’s space history website (, and in “The Lunar Roving Vehicle—Historical Perspective,” at

1972, Lunar Highlands

A spectacular series of virtual-reality animated panoramas of all the Apollo landing sites can be explored online at

1972, Last on the Moon

An excellent place to start to learn more about the six Apollo moon landings, and other missions in the Apollo program, is Wikipedia’s “Apollo program” Web page at

1973, Gamma-Ray Bursts

The original 1973 Astrophysical Journal (vol. 182) paper announcing the discovery of GRBs, “Observations of Gamma-Ray Bursts of Cosmic Origin” by Ray W. Klebesadel, Ian B. Strong, and Roy A. Olson, is available online at….

1973, Pioneer 10 at Jupiter

More details about the plaque carried by the Pioneer 10 and 11 spacecraft, as well as the Golden Record carried by the follow-on Voyager 1 and 2 spacecraft, can be found in the book Murmurs of Earth: The Voyager Interstellar Record, by Carl Sagan and colleagues (New York: Ballantine, 1978).

1976, Vikings on Mars

The first edition of Mike Carr’s beautifully illustrated book The Surface of Mars (New Haven, CT: Yale University Press, 1981) was a definitive summary of our knowledge of Martian geology from the Viking and Mariner missions up until the mid-1990s.

1977, Voyager “Grand Tour” Begins

University of Hawaii professor David Swift’s engaging book Voyager Tales: Personal Views of the Grand Tour (Reston, VA: American Institute of Aeronautics and Astronautics, 1997) is full of amazing firsthand stories by the men and women who designed and conducted Voyager’s Grand Tour of the outer solar system.

1977, Uranian Rings Discovered

An exciting personal account of the discovery of the Uranian rings was described in a book by my late planetary science colleague Jim Elliot (their codiscoverer) and Richard Kerr in Rings: Discoveries from Galileo to Voyager (Cambridge, MA: MIT Press, 1987).

1978, Discovery of Charon

Charon was the last major (nonirregular) satellite of a classical planet to be discovered by telescope; for a chronological list of all of the satellites that have been discovered in our solar system (by telescope or spacecraft), see…

1978, Ultraviolet Astronomy

In case you forget, NASA’s Imagine the Universe! website, hosted by the Goddard Space Flight Center, has a helpful, illustrated primer on the definitions of the types of electromagnetic radiation: ultraviolet, visible, infrared, radio, gamma-ray, and more. Check it out at

1979, Active Volcanoes on Io

Rosaly Lopes and Michael Carroll’s beautiful book Alien Volcanoes (Baltimore: Johns Hopkins University Press, 2008) contains spectacular images and other information about Io’s volcanoes as well as volcanoes on other planets.

1979, Jovian Rings

NASA’s Planetary Data System has a Planetary Rings Node website ( that provides access to all kinds of information and data about Jupiter’s rings, as well as the rings around Saturn, Uranus, and Neptune.

1979, An Ocean on Europa?

Richard J. Greenberg’s Europa: The Ocean Moon (New York: Springer, 2005) is a well-written and entertaining summary of both historical and recent observations of Europa, including the evidence for its subsurface ocean.

1979, Gravitational Lensing

Wikipedia’s “Gravitational lens” page at contains a number of excellent visualizations and animations that help further explain the concept.

1979, Pioneer 11 at Saturn

NASA Special Publication 349 (Washington, D.C.: NASA Scientific and Technical Information Office, 1977), called Pioneer Odyssey, is a richly illustrated history of the Pioneer 10 and 11 projects—and it’s available online at

1980, Cosmos: A Personal Voyage

Joining the Planetary Society (, a nonprofit, public space-advocacy and education organization founded by Carl Sagan, Bruce Murray, and Louis Friedman in 1980, is a great way to stay current with and directly participate in planetary and space exploration.

1980, 1981, Voyager Saturn Encounters

Arizona State University history professor Stephen Pyne describes the Voyager missions in the context of past missions of exploration to discover new lands (on Earth) in his recent book Voyager: Seeking New Worlds in the Third Great Age of Discovery (New York: Viking, 2010).

1981, Space Shuttle

With the retirement of the space shuttle fleet in 2011, what comes next for US human spaceflight? A presidential commission in 2009 recommended that NASA take a “flexible path” to future destinations, enabling missions to the Moon, Mars, or asteroids (see No specific missions have yet been formulated, however.

1982, Rings around Neptune

The current scholarly bible for the latest information on ring science, at Neptune and the other giant planets, is Larry Esposito’s Planetary Rings (New York: Cambridge University Press, 2006).

1983, Pioneer 10 beyond Neptune

You can monitor information on the five NASA spacecraft that are on their way out of our solar system at

1984, Circumstellar Disks

University of California at Berkeley astronomer Paul Kalas maintains a Circumstellar Disk Learning Site ( where you can find images, links, and more information about these important indicators of planetary formation.

1989, Voyager 2 at Uranus

Voyager 2 is as yet the only spacecraft to visit Uranus. However, in 2011, NASA’s Planetary Decadal Survey for 2013–2022 called for a possible Uranus orbiter mission to follow up Voyager 2’s discoveries at Uranus, much as Galileo and Cassini did previously at Jupiter and Saturn. Download the survey’s report from for details.

1987, Supernova 1987A

A French research team has assembled a spectacular time-lapse movie of so-called light echoes (light waves reflected off of other sources—analogous to sound echoes) from Supernova 1987A between 1996 and 2002. The movie is posted online at

1988, Light Pollution

You can learn more about the important work of the International Dark-Sky Association (and join!) at

1989, Voyager 2 at Neptune

The 1995 University of Arizona Space Science Series book Neptune and Triton (Dale P. Cruikshank, ed.) will likely remain an authoritative source of scientific information on the Neptune system for a long time, as no new missions to the eighth planet are being planned for the near future.

1989, Walls of Galaxies

Astronomer Stephen D. Landy wrote a nice introduction to the concept of large-scale cosmic structures (including walls of galaxies) in “Mapping the Universe,” in the June 1999 issue of Scientific American.

1990, Hubble Space Telescope

The Hubble Site ( is a one-stop Internet shop for an amazing collection of information, stories, and glorious pictures of the cosmos taken by the Hubble Space Telescope.

1990, Venus Mapped by Magellan

My planetary science colleague David Grinspoon worked closely with Magellan Venus mission data, and his book Venus Revealed: A New Look Below the Clouds of Our Mysterious Twin Planet (New York: Basic Books, 1998) is a fun and personal look at the history and science of Earth’s “twin” planet.

1991, Gamma-Ray Astronomy

NASA’s Imagine the Universe! website offers a great online “History of Gamma-Ray Astronomy” at

1992, Mapping the Cosmic Microwave Background

Two leading COBE scientists, John Mather and George Smoot, received the 2006 Nobel Prize in Physics for their work on helping to create a new era of precision observational cosmology using space-based missions such as COBE.

1992, First Extrasolar Planets

Twelve more candidate planets have now been detected around eleven other pulsars besides those around PSR B1257+12. See the Extrasolar Planet Encyclopaedia at for updates and details.

1992, Kuiper Belt Objects

The International Astronomical Union’s Minor Planet Center is now tracking more than 1,250 trans-Neptunian objects in the Kuiper belt, and the population continues to grow (see the list at

1992, Asteroids Can Have Moons

Finding a moon around an asteroid is more than just cool: it allows astronomers to determine the mass of the asteroid (using Kepler’s laws) and, knowing or estimating the shape and size, its density as well. Density gives clues about composition (ice, rock, metal) and interior structure (coherent rock or rubble pile).

1993, Giant Telescopes

Wikipedia hosts a list of the world’s largest optical telescopes, both in historical and modern times, at….

1994, Comet SL-9 Slams into Jupiter

A beautiful collection of photos and stories from an amazing two weeks in the summer of 1994 has been compiled by planetary science colleagues John Spencer and Jacqueline Mitton in The Great Comet Crash: The Collision of Comet Shoemaker-Levy 9 and Jupiter (New York: Cambridge University Press, 1995).

1994, Brown Dwarfs

Weather patterns on brown dwarfs could be quite wild—rain made of liquid iron falling through an atmosphere made of vaporized rock, for example. Check out the interview with some brown dwarf researchers in Jeanna Bryner’s article “Wild Weather: Iron Rain on Failed Stars,” at for more details.

1995, Planets around Other Suns

The Extrasolar Planets Encyclopaedia’s “Interactive Extra-solar Planets Catalog,” hosted online by the Paris Observatory, keeps an up-to-date list of extrasolar planets discovered by all the different methods used by astronomers. The catalog can be found at

1995, Galileo Orbits Jupiter

For all the insider details about the Galileo mission, see NASA Special Publication 4231, Mission to Jupiter: A History of the Galileo Project (2007), by Michael Meltzer, available online at

1996, Life on Mars?

The National Space Science Data Center has a dedicated Web page with information and links about the ALH84001 controversy (“Evidence of Ancient Martian Life in Meteorite ALH84001?”), online at

1997, “Great Comet” Hale-Bopp

Noted amateur astronomer and comet researcher Gary W. Kronk has compiled a great collection of information and links about comet Hale-Bopp on his “Cometography” Web page about the comet at

1997, 253 Mathilde

Since Mathilde is jet black and likely contains a significant amount of carbon, the naming theme chosen for craters and other features on its surface was coal fields and coal basins on the Earth. See for a list of the naming themes used on all the solar system bodies studied so far.

1997, First Rover on Mars

To get a feel for the Sojourner rover in action, check out the time-lapse rover “movies” created by NASA/Jet Propulsion Laboratory planetary scientist Justin Maki and the Mars Pathfinder team, online at

1997, Mars Global Surveyor

The MGS Mars Orbiter Camera (MOC) was the highest-resolution camera sent to Mars at the time. The team from Malin Space Science Systems, Inc., that built and operated the camera created a spectacular collection of greatest-hits photos (many with scientific annotation) from MOC and their other Mars cameras online at

1998, International Space Station

A fascinating animation showing the assembly sequence for the ISS between 1998 and 2011 can be found at

1998, Dark Energy

The website at and the April 2009 Scientific American article “Does Dark Energy Really Exist?” (by Timothy Clifton and Pedro G. Ferreira) are great resources for more information about the strange and puzzling force known as dark energy.

1999, Earth’s Rotation Speeds Up

Wikipedia’s “Leap second” page at provides a fascinating and detailed account of the history, implementation, and controversy surrounding this curious feature of modern timekeeping.

1999, Torino Impact Hazard Scale

More details about the Torino Impact Hazard Scale as well as the more recent Palermo Technical Impact Hazard Scale now used among many professional astronomers can be found online at and, respectively.

1999, Chandra X-ray Observatory

The place to go to learn more about Chandra and X-ray astronomy, and to see spectacular examples of images, is the Chandra X-ray Observatory Center website, at

2000, An Ocean on Ganymede?

To me, Ganymede is really a planet—larger than Mercury; differentiated into core, mantle, and crust; deep ocean; its own magnetic field . . . it’s a planet that just happens to be in orbit around Jupiter. It’s no wonder that the European Space Agency has decided to launch a dedicated Ganymede orbiter mission in 2022 called the Jupiter Icy Moons Explorer to focus on the exploration of this fascinating world. See for more details.

2000, NEAR at Eros

The National Space Science Data Center hosts a variety of time-lapse animations (and other data) of Eros from the NEAR mission, at

2001, Solar Neutrino Problem

An interesting history of neutrinos and the 1970–2002 astronomical detective story known as the “solar neutrino problem” can be found in Arthur B. McDonald, Joshua R. Klein, and David L. Wark’s “Solving the Solar Neutrino Problem” (Scientific American 288, no. 4 [April 2003], pp. 40–49).

2001, Age of the Universe

Besides WMAP and HST, other methods of estimating the age of the universe come from estimating ages of the oldest stars in globular clusters, the oldest white dwarfs, and radioactive dating of meteorites combined with modeling of the time for heavy elements to form in supernova explosions. All the methods give results in the range of 10 to 20 billion years. See “How Old Is the Universe,” by John Carl Villanueva, at for more details.

2001, Genesis Catches Solar Wind

The technical details of the Genesis mission results have been published by D. Burnett and the Genesis Science Team in “Solar Composition from the Genesis Discovery mission,” Proceedings of the National Academy of Sciences of the United States, May 9, 2011, (online at

2003, Spitzer Space Telescope

Spitzer’s home page ( has a fantastic collection of astronomical images and features about the science of infrared astronomy.

2004, Spirit and Opportunity on Mars

If you like space-related picture books, you might be interested my large-format coffee table book called Postcards from Mars (New York: Dutton, 2006), or my fun stereo-viewer book called Mars 3-D (New York: Sterling, 2008), showcasing the stories and photographic highlights from the Spirit and Opportunity rover missions.

2004, Cassini Explores Saturn

Saturn from Cassini-Huygens (Michele K. Dougherty, Larry W. Esposito, and Stamatios M. Krimigis, eds.), published by Springer (2009), is a comprehensive, scholarly summary of the latest results from the incredibly successful Cassini-Huygens mission at the solar system’s most famous ringed planet and its moon Titan.

2004, Stardust Encounters Wild-2

The December 15, 2006, issue of Science magazine contains a variety of papers presenting the first detailed analysis of the chemistry and mineralogy of the Stardust samples.

2005, Deep Impact: Tempel-1

A collection of cool animations of the Deep Impact projectile’s crash into Tempel-1 is posted at

2005, Huygens Lands on Titan

A nice summary of our current knowledge of Titan appeared in “The Moon That Would Be a Planet,” by Ralph Lorenz and Christophe Sotin, in the March 2010 issue of Scientific American.

2005, Hayabusa at Itokawa

The February 2011 online issue of Planetary Science Research Discoveries (published by the University of Hawaii Institute of Geophysics and Planetology) contains details and links to more information about the tiny samples of Itokawa returned by Hayabusa:

2005, Shepherd Moons

The Cassini Imaging Central Library for Operations (CICLOPS) website at contains spectacular examples of ring and shepherd moon images, as well as great descriptions from team members about the work being done with Cassini images.

2006, Demotion of Pluto

The new IAU definition of “planet” is described in detail at, along with a discussion of the ensuing debate and controversy.

2007, Habitable Super Earths?

Excitement continues to mount about the potential habitability of Gliese 581 d in particular, based on new computer models of its possible climate. For details, see “First Habitable Exoplanet? Climate Simulation Reveals New Candidate That Could Support Earth-Like Life,” at

2007, Hanny’s Voorwerp

Check out—or join in with—Galaxy Zoo at and the Stardust@Home project at

2009, Kepler Mission

Visit the Kepler mission’s home page at for details on the mission and the latest science results.

2010, SOFIA

Photos and other information about the airborne observatory’s goals, its instruments, and the airplane itself can be browsed online at the SOFIA Science Center site:

2010, Rosetta Flies by Lutetia

Blogger and planetary scientist Emily Lakdawalla from the Planetary Society describes the details of her mosaic comparing Lutetia with the other asteroids and comets visited by spacecraft in this blog entry:

2010, Comet Hartley-2

Details and references regarding analysis of Deep Impact and telescopic observations of Hartley-2 are continually updated at

2011, MESSENGER at Mercury

The MESSENGER mission’s Internet home page at is the place to go for the latest photos and other results from the ongoing orbital mission at Mercury.

2011, Dawn at Vesta

My articles “Dawn’s Early Light: A Vesta Fiesta!” and “Protoplanet Closeup” in the November 2011 and September 2012 issues of Sky & Telescope magazine provide additional details and images from the Dawn mission’s orbital encounter with Vesta. See also for the latest images.

2012, Mars Science Laboratory Curiosity Rover

Photos and movies of the Curiosity rover being built and tested, and a computer-animated simulation of the rover’s “sky crane” landing on Mars in August 2012 can all be viewed from the mission’s main website at

2015, Pluto Revealed!

Keep up with the latest information leading up to the summer 2015 flyby of Pluto at the New Horizons team website:

2017, North American Solar Eclipse

NASA Goddard Space Flight Center’s eclipse guru Fred Espenak keeps a detailed, updated set of Web pages on upcoming solar and lunar eclipses and planetary transits at

2018, James Webb Space Telescope

If you’re interested in learning more of the nitty-gritty scientific and technical details about JWST, then you’ll love the article by deputy project scientist Jonathan P. Gardner and his colleagues in Space Science Reviews (123 [2006], pp. 485–606, available online at

2029, Apophis Near Miss

The details of Apophis’s 2036 close approach to Earth depend on exactly where it passes the Earth and Moon in 2029 and how its trajectory responds to subtle variations in the Earth’s and Moon’s gravity fields that cannot be perfectly modeled in the computer. But better orbit measurements in 2013 using the Arecibo radio telescope should help reduce the uncertainties further.

~2035-2050, First Humans on Mars?

There are no insurmountable technical or engineering challenges to starting a human mission to Mars. Sadly, the major obstacles appear to be the lack of sufficient government funding to develop a reliable deep space (beyond low-Earth orbit) rocket, capsule, landing, and return system, and the lack of national will to see such an adventure occur. The latter will be required to surmount the former.

~100 Million Years from Now, Sagittarius Dwarf Galaxy Collision

For more background and details on galaxy collisions and mergers, see “How Does Your Galaxy Grow?” by Eugenie Samuel Reich in the July 17, 2009, issue of New Scientist magazine.

~1 Billion Years from Now, Earth’s Oceans Evaporate

Penn State University climate scientist Jim Kasting and colleagues have contributed to the climate modeling work that predicts the oceans’ evaporation in about a billion years; see “Earth’s Oceans Destined to Leave in Billion Years” at

3–5 Billion Years from Now, Collision with Andromeda

A spectacular computer-animated simulation of the collision and merger of the Milky Way and Andromeda-like galaxies is posted on the Hubble Space Telescope’s website at….

5–7 Billion Years from Now, End of the Sun

The fate of the Sun is described in great detail in stellar astronomer James B. Kaler’s Stars (New York: Scientific American Library, 1992).

~1014 Years from Now, Last of the Stars

Ideas about the end of the so-called stelliferous era of star formation vary; I think that the nice video and text description in “The Decay of Heaven” by amateur astronomer Tony Darnell, at the Deep Astronomy website (, does a great job of capturing the essentials of what is likely to occur in the far future.

~1017–1037 Years from Now, Degenerate Era

For more details on this and other likely major milestones in the life of the universe, I recommend Fred C. Adams and Greg Laughlin’s The Five Ages of the Universe: Inside the Physics of Eternity (New York: Free Press, 1999).

~1037–10100 Years from Now, Black Holes “Evaporate”

For some mind-bending ideas about possibly creating evaporating black holes in the laboratory, check out “Quantum Black Holes” by astrophysicists Bernard J. Carr and Steven B. Giddings in the May 2005 issue of Scientific American.

The End of Time, How Will the Universe End?

If you’ve never contemplated the end of time as a potential tourist destination, I highly recommend Douglas Adams’s The Restaurant at the End of the Universe, originally published in 1980—after, of course, reviewing The Hitchhiker’s Guide to the Galaxy, first published in 1979.