Notes and Further Reading
I consulted a huge number of resources during the research for this book, including 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. To save space, I use the tinyurl.com format for many Web sites; full URLs and other details can be found on my web site at jimbell.sese.asu.edu/space-book. The Internet is dynamic, and so some of the sites pointed to below may not be in use by the time this book appears in print.
Selecting just 250 milestones in the entire history of astronomy and space exploration 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 would also welcome any corrections or general feedback. Please feel free to contact me via Jim.Bell@asu.edu or jimbell.sese.asu.edu/contact.
General Reading
Beatty, J.K., C.C. Petersen, and A. Chaikin, eds. The New Solar System. Cambridge, UK: Cambridge Univ. Press, 1998.
Levy, D.H., ed. The Scientific American Book of the Cosmos. New York: St. Martin’s Press, 2000.
Mitton, S., ed. The Cambridge Encyclopaedia of Astronomy. Cambridge, UK: Cambridge Univ. Press, 2001.
Moore, P., ed. Astronomy Encyclopedia. Oxford, UK: Oxford Univ. Press, 2002.
Weissman, P.R., L.A. McFadden, and T.V. Johnson, eds. Encyclopedia of the Solar System. San Diego, CA: Academic Press, 1999.
General-Interest Web Sites
Curious about Astronomy? Ask an Astronomer: curious.astro.cornell.edu
Nine Planets: nineplanets.org
Views of the Solar System: www.solarviews.com
Bad Astronomy (blog): blogs.discovermagazine.com/badastronomy
Wikipedia: www.wikipedia.org
c. 13.7 Billion BCE, Big Bang
See “Misconceptions about the Big Bang” by C. Lineweaver and T. Davis (Scientific American, Feb. 2005) and “The First Few Microseconds” by M. Riordan and W. Zajc (Scientific American, Apr. 2006).
c. 13.7 Billion BCE, Recombination Era
Using data from the WMAP satellite, cosmologists determined the start of the recombination era to a stunningly accurate 380,000 years after the Big Bang. The results named Science magazine’s “breakthrough of the year” for 2003 (see Science, Dec. 19, 2003).
c. 13.5 Billion BCE, First Stars
Cosmologist Volker Bromm and colleagues at the Univ. of Texas at Austin host tutorials, papers, and computer animations about the first stars and galaxies at tinyurl.com/brdqoxx.
c. 13.3 Billion BCE, Milky Way
A very nice series of maps and photographs of the Milky Way can be found at Atlas of the Universe: tinyurl.com/2fooye.
c. 5 Billion BCE, Solar Nebula
The generally accepted father of the modern solar nebular disk model is Soviet astronomer Victor Safronov (1917–1999); his book Evolution of the Protoplanetary Cloud and the Formation of the Earth and the Planets (NASA Tech. Trans. F-677, 1972) is a classic text.
c. 4.6 Billion BCE, Violent Proto-Sun
Australia Telescope Outreach and Education: tinyurl.com/c4ey6en.
c. 4.6 Billion BCE, Birth of the Sun
Spectacular photos, movies, and other information about the Sun can be found at the ESA/NASA Solar and Heliospheric Observatory (SOHO) web site: tinyurl.com/thyo.
c. 4.5 Billion BCE, Mercury
Strom, R.G., Mercury: The Elusive Planet (Cambridge, UK: Cambridge Univ. Press, 1987).
c. 4.5 Billion BCE, Venus
Find Venus at nineplanets.org/venus.html.
c. 4.5 Billion BCE, Earth
Dalrymple, G.B., The Age of the Earth (Stanford, CA: Stanford Univ. Press, 1994).
c. 4.5 Billion BCE, Mars
The Planetary Society, the world’s largest public space-advocacy organization, hosts information devoted to the exploration of Mars: tinyurl.com/cntykwg.
c. 4.5 Billion BCE, Main Asteroid Belt
Details about more than a half million minor planets in the main asteroid belt and elsewhere in the solar system are compiled by the International Astronomical Union’s Minor Planet Center at tinyurl.com/d2scxfv.
c. 4.5 Billion BCE, Jupiter
Bagenal, F., T.E. Dowling, and W.B. McKinnon, eds., Jupiter: The Planet, Satellites, and Magnetosphere (New York: Cambridge Univ. Press, 2007).
c. 4.5 Billion BCE, Saturn
Saturn’s atmosphere is less dynamic than Jupiter’s, but still reveals interesting and enigmatic features, such as a bright new storm system that became visible in 2010: tinyurl.com/24prgxd.
c. 4.5 Billion BCE, Uranus
A wonderful collection of photos of the Uranian atmosphere, rings, and moons can be found on the NASA Planetary Photojournal site for Uranus: tinyurl.com/6pzdykv.
c. 4.5 Billion BCE, Neptune
The idea that Uranus and Neptune have migrated outward since their formation is discussed in “The Chaotic Genesis of Planets” by D.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: tinyurl.com/d6q9ckf.
c. 4.5 Billion BCE, Birth of the Moon
Canup, R.M., and K. Righter, eds., The Origin of the Earth and Moon (Tucson: Univ. of Arizona Press, 2000).
c. 4.1 Billion BCE, Late Heavy Bombardment
The giant planets likely played a significant role in the late heavy bombardment: tinyurl.com/csg6zh4.
c. 3.8 Billion BCE, Life on Earth
Ricardo, A. and J.W. Szostak, “The Origin of Life on Earth,” Scientific American, Sep. 2009.
550 Million BCE, Cambrian Explosion
Erwin, D.H., Extinction: How Life on Earth Nearly Ended 250 Million Years Ago (Princeton, NJ: Princeton Univ. Press, 2006).
65 Million BCE, Dinosaur-Killing Impact
For more details and references about the controversy surrounding the impact hypothesis, a great place to start is Wikipedia’s K-T extinction event page: tinyurl.com/mm2dz.
200,000 BCE, Homo Sapiens
Seed magazine reporter Holly Capelo wrote an interesting summary of recent evidence that Paleolithic cave art may capture some aspects of ancient astronomical and celestial lore: tinyurl.com/cvgtd6q.
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: tinyurl.com/bqsgdsb.
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 latter word).
c. 3000 BCE, Ancient Observatories
Newham, C.A., The Astronomical Significance of Stonehenge (Warminster, UK: Coates & Parker, 1993).
c. 2500 BCE, Egyptian Astronomy
I remember reading an early edition of E.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
Univ. of Maine professor Marilyn Shea highlights many ancient Chinese astronomers and astronomical instruments at tinyurl.com/cxqtavp.
c. 500 BCE, Earth Is Round!
If you’re still not convinced 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: tinyurl.com/346e6c8.
c. 400 BCE, Greek Geocentrism
According to Bakersfield College astronomy professor Nick Strobel (tinyurl.com/blcrvgf), 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
Andrew Fraknoi of Foothill College (Los Altos Hills, California) and the Astronomical Society of the Pacific have excellent pointers and resources for those who want to debunk astronomy-related pseudoscience: tinyurl.com/yfbp4vy.
c. 280 BCE, Sun-Centered Cosmos
Kragh, H.S., Conceptions of Cosmos—From Myths to the Accelerating Universe: A History of Cosmology (New York: Oxford Univ. Press, 2007).
c. 250 BCE, Eratosthenes Measures the Earth
Since 2000, Follow the Path of Eratosthenes has enabled students to reproduce his more than 2,200-year-old experiment on their own: tinyurl.com/d7bd2k3.
c. 150 BCE, Stellar Magnitude
Still confused about the backward stellar magnitude system used by astronomers? Sky & Telescope magazine contributor Alan MacRobert’s article at tinyurl.com/luxflk might help.
c. 100 BCE, First Computer
See D.J. de Solla Price’s “An Ancient Greek Computer” (Scientific American, June 1959) and Tony Freeth’s “Decoding an Ancient Computer” (Scientific American, Dec. 2009).
45 BCE, Julian Calendar
Web Exhibits: tinyurl.com/58ctv5.
c. 150 Ptolemy’s Almagest
See physics professor Dennis Duke’s “Ancient Planetary Model Animations” (tinyurl.com/blh7uql).
185, Chinese Observe “Guest Star”
Astronomers using NASA’s Spitzer Space Telescope and WISE satellite have pieced together the details of the supernova of 185 to explain its progression from the bright flash first observed to the roughly spherical remnants of gas and dust visible today (tinyurl.com/88sosvy).
c. 500, Aryabhatiya
Walter E. Clark’s 1930 English translation of the Aryabhatiya: tinyurl.com/chbvjet.
c. 700, Finding Easter
You can check Venerable Bede’s calculations of the date of Easter using modern computus methods at the Astronomical Society of South Australia’s website: tinyurl.com/9zsa.
c. 825, Early Islamic Astronomy
A useful and educational introductory reference on early Arabic astronomy is Owen Gingerich’s “Islamic Astronomy” (Scientific American, Apr. 1986).
c. 964, Andromeda Sighted
Persian astronomer ‘Abd al-Rahmān al-Sūfī’s The Book of the Fixed Stars is available via the World Digital Library: tinyurl.com/cx7mkdr.
c. 1000, Experimental Astrophysics
More details about the lives and work of al-Haytham and al-Bīrūnī can be found in recent articles by Prof. Jim Al-Khalili (tinyurl.com/8q5k9c), and author Richard Covington (tinyurl.com/2wqe7t).
c. 1000, Mayan Astronomy
A high-resolution version of the complete Dresden Codex can be downloaded from tinyurl.com/d5f38vq. See also Prof. Anthony Aveni’s Conversing with the Planets: How Science and Myth Invented the Cosmos (New York: Kodansha International, 1994).
1054, “Daytime Star” Observed
Mitton, S., The Crab Nebula (New York: Charles Scribner’s Sons, 1979).
c. 1230, De Sphaera
Learn a lot more about John of Sacrobosco at tinyurl.com/cbbvrsd.
c. 1260, Large Medieval Observatories
NASA’s Ancient Observatories, Timeless Knowledge: tinyurl.com/cl4busr.
c. 1500, Early Calculus
The figure is adapted from Ramasubramanian, K., et al., “Modification of the Earlier Indian Planetary Theory by the Kerala Astronomers (c. 1500) and the Implied Heliocentric Picture of Planetary Motion” (Current Science, vol. 66, 784–790, 1994).
1543, Copernicus’s De Revolutionibus
Helden, A.V.: tinyurl.com/cebcm.
1572, Brahe’s “Nova Stella”
Thoren, V.E., The Lord of Uraniborg: A Biography of Tycho Brahe (New York: Cambridge Univ. Press, 1990).
1582, Gregorian Calendar
The US Naval Observatory’s “Introduction to Calendars” (tinyurl.com/d589vr8) summarizes the six principal calendar systems currently in worldwide use.
1596, Mira Variables
Hoffleit, D.: tinyurl.com/ct3mzgy.
1600, Bruno’s On the Infinite Universe and Worlds
Wikipedia’s “Giordano Bruno” page (tinyurl.com/ayqfd) provides a starting point for 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 tinyurl.com/bpbbqqn; also see “The Telescope” from the Rice Univ. Galileo Project at tinyurl.com/33gat4u.
1610, Galileo’s Starry Messenger
Museo Galileo provides details about Galileo’s telescope at tinyurl.com/d2n945d. For more personal revelations, see Dava Sobel’s Galileo’s Daughter: A Historical Memoir of Science, Faith, and Love (New York: Walker & Co., 2011).
1610, Io
Lopes, R.M.C. and J.R. Spencer, eds., Io After Galileo: A New View of Jupiter’s Volcanic Moon, edited by (Chichester, UK: Springer/Praxis, 2006).
1610, Europa
Spectacular views of Europa can be found on the NASA Planetary Photojournal search page: tinyurl.com/cw7pz7w.
1610, Ganymede
For more of the history of orbital resonances and celestial dynamics, see C.D. Murray and S.F. Dermott’s Solar System Dynamics (New York: Cambridge Univ. Press, 2000).
1610, Callisto
Visit Dr. Paul Schenk’s 3D House of Satellites blog (tinyurl.com/bssr43w) 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 E.C. Krupp’s article “Igniting the Hearth,” Sky & Telescope (Feb. 1999).
1619, Three Laws of Planetary Motion
More about Johannes Kepler can be found in C. Wilson’s “How Did Kepler Discover His First Two Laws?” (Scientific American, March 1972) and O. 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 W. Sheehan and J. Westfall’s The Transits of Venus (Amherst, NY: Prometheus, 2004).
1650, Mizar-Alcor Sextuple System
Kaler, J.: tinyurl.com/yezwdhv; see also L. Ondra’s “A New View of Mizar,” originally published in Sky & Telescope (July 2004) and available at tinyurl.com/bqjaeh4.
1655, Titan
Huygens’s Systema Saturnium is available from the Smithsonian Institution Libraries at tinyurl.com/bpwdunv.
1659, Saturn Has Rings
NASA Planetary Data System’s “Saturn’s Rings”: tinyurl.com/d28nu2n; see also the previous note.
1665, Great Red Spot
A.P. Ingersoll reviews the history and science of the Great Red Spot in “Atmospheres of the Giant Planets,” chapter 15 in The New Solar System, edited by J.K. Beatty, C.C. Petersen, and A. Chaikin (Cambridge, MA: Sky Publishing, 1999).
1665, Globular Clusters
National Optical Astronomy Observatories: tinyurl.com/abjnve.
1671–1672, Iapetus and Rhea
See the Cassini mission’s “Iapetus” Web page: tinyurl.com/7l6yghw.
1676, Speed of Light
See also S. Soter and N.D. Tyson (eds.), Cosmic Horizons: Astronomy at the Cutting Edge (New York: New Press, 2001).
1682, Halley’s Comet
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 IAU’s Minor Planet Center at tinyurl.com/28y8a5r.
1684, Tethys and Dione
NASA Planetary Photojournal: tinyurl.com/c24cvnh.
1684, Zodiacal Light
Details of the early history of zodiacal light observations can be found in C. E. Brame’s “The Zodiacal Light” (Popular Science Monthly, July 1877, available at tinyurl.com/bstncr3.
1686, Origin of Tides
Excellent introductory discussions of tides can be found at “How Tides Work” on E. Siegel’s blog Starts with a Bang! (tinyurl.com/2axmfap) and “Tidal Misconceptions” by D. Simanek (tinyurl.com/lhm5ac), as well as pages 265–274 in V.D. Barger and M.G. Olsson’s Classical Mechanics: A Modern Perspective (New York: McGraw-Hill, 1973).
1687, Newton’s Laws of Gravity and Motion
Hawking, S., On the Shoulders of Giants: The Great Works of Physics and Astronomy, (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 R.G. Aitken’s “Edmund Halley and Stellar Proper Motions” (Astronomical Society of the Pacific Leaflets, Oct. 1942), available at tinyurl.com/c8mxavz.
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 at tinyurl.com/c6pxcpl.
1764, Planetary Nebulae
Details on Hubble Space Telescope images of the Cat’s Eye and other planetary nebulae can be found at tinyurl.com/cuoaxur.
1771, Messier Catalog
Various compilations and links to “Messier marathon” sites can be found via the Paris Observatory (tinyurl.com/bt5kq46), and from the Students for the Exploration and Development of Space (tinyurl.com/cqygeww). Also, an English translation of Messier’s original 1771 catalog of the first 45 objects is online at tinyurl.com/c99ascl.
1772, Lagrange Points
Astrophysicist Neil deGrasse Tyson discusses the history, physics, and space exploration potential of Lagrange points at tinyurl.com/bmqhark.
1781, Discovery of Uranus
Lemonick, M., The Georgian Star: How William and Caroline Herschel Revolutionized Our Understanding of the Cosmos (New York: W.W. Norton, 2009).
1787, Titania and Oberon
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, (January 1, 1787); it is online at tinyurl.com/dyou62p.
1789, Enceladus
“Cassini Images of Enceladus Suggest Geysers Erupt Liquid Water at the Moon’s South Pole”: tinyurl.com/8k4d6g2.
1789, Mimas
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 (vol. 50, 114–118, 1927): tinyurl.com/8dyosha.
1794, Meteorites Come from Space
Smith, C., S. Russell, and G. Benedix,Meteorites (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 Nov./Dec. 2007 issue of American Scientist, online at www.americanscientist.org/issues/pub/the-inimitable-caroline.
1801, Ceres
Hubble Space Telescope photos of both 1 Ceres and 4 Vesta can be found on astronomy professor C. Seligman’s website: tinyurl.com/blemkol.
1807, Vesta
An excellent recent scientific summary of asteroid research is Asteroids III (Tucson: Univ. of Arizona Press, 2002), edited by W.F. Bottke and colleagues. It includes a chapter by Prof. K. Keil, entitled “Geological History of Asteroid 4 Vesta: The Smallest Terrestrial Planet” (pp. 573–584), online at tinyurl.com/blf4765.
1814, Birth of Spectroscopy
An online biography of Joseph von Fraunhofer’s life and achievements is at tinyurl.com/c4bkbcv.
1838, Stellar Parallax
The accompanying photo is a screen shot from a wonderful Web application by V. Bodurov that lets you view the stars in the Sun’s neighborhood from any direction: tinyurl.com/9htgzzq.
1839, First Astrophotographs
The Hastings Historical society has detailed background about John Draper’s and his son Henry’s astronomical photography at tinyurl.com/8fd5pmd and tinyurl.com/8hpad5n.
1846, Discovery of Neptune
An engaging history of the discovery of Neptune is British astronomer Sir Patrick Moore’s 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, et al., 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 at the Maria Mitchell Association (tinyurl.com/9ke5z2y), “founded in 1902 to preserve the legacy of Nantucket native astronomer, naturalist, librarian, and, above all, educator.”
1848, Doppler Shift of Light
Wright, N.: tinyurl.com/ygjz7t2.
1848, Hyperion
Thomas, P.C., et al., “Hyperion’s Sponge-like Appearance” (Nature vol. 448, pp. 50–56, 2007).
1851, Foucault’s Pendulum
California Academy of Science: tinyurl.com/yhn3g8.
1851, Ariel and Umbriel
Read a detailed account of the life of William Lassell in his 1880 obituary in The Observatory (vol. 3, pp. 586–590, 1880), online at tinyurl.com/9qetb93.
1857, Kirkwood Gaps
Fernie, J.D., “The American Kepler” (American Scientist, Sept./Oct. 1999: tinyurl.com/8tmjpyt.
1859, Solar Flares
“NASA Science News: A Super Solar Flare” (May 6, 2008): tinyurl.com/32v6amx.
1859, Search for Vulcan
Fontenrose, R., “In Search of Vulcan” (J. History of Astronomy vol. 4, p. 145, 1973): tinyurl.com/95ua9fn.
1862, White Dwarfs
An outstanding account of the history and legacy of telescope makers Alvan Clark and Sons is D.J. Warner and R.B. Ariail’s Alvan Clark & Sons: Artists in Optics (Richmond, VA: Willmann-Bell, 1995).
1866, Source of the Leonid Meteors
Kronk, G.: tinyurl.com/8zw8e8d.
1868, Helium
The Wikipedia entry on helium at tinyurl.com/n5of7 contains extensive details and references.
1877, Deimos and Phobos
A personal account of Asaph Hall’s discovery of the moons of Mars is “The Discovery of the Satellites of Mars” (Monthly Notices of the Royal Astronomical Society vol. 38, pp. 205–209, 1878), online at tinyurl.com/9cy46pc. Details about the Mars rovers’ observations of the solar transits of both moons can be found in an article that colleagues and I wrote: “Solar Eclipses of Phobos and Deimos Observed from the Surface of Mars” (Nature vol. 436, pp. 55–57, 2005).
1887, End of the Ether
Michelson and Morley’s original paper was published as “On the Relative Motion of the Earth and the Luminiferous Ether” in the American Journal of Science (vol. 34, pp. 333–345, 1887): tinyurl.com/92vz92u.
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: tinyurl.com/32r8ue.
1895, Milky Way Dark Lanes
A summary of Max Wolf’s astronomical career can be found in J.S. Tenn’s “Max Wolf: The Twenty-Fifth Bruce Medalist” (Mercury, July–Aug. 1994): tinyurl.com/9sm5xt8.
1896, Greenhouse Effect
United Nations’ Intergovernmental Panel on Climate Change Fourth Assessment Report: tinyurl.com/aprync.
1896, Radioactivity
Hedman, M., The Age of Everything: How Science Explores the Past (Chicago: Univ. of Chicago Press, 2007).
1899, Phoebe
Cassini mission’s “Phoebe” Web page: tinyurl.com/9nh95kz.
1900, Quantum Mechanics
New Scientist: tinyurl.com/ca8lnx.
1901, Pickering’s “Harvard Computers”
Nelson, S., “The Harvard Computers” (Nature vol. 455, 36–37, Sept. 4, 2008).
1904, Himalia
Animated orbital views of the irregular satellites of all of the giant planets can be seen with the Univ. of Maryland’s online Solar System Visualizer: tinyurl.com/2acvd7.
1905, Einstein’s “Miracle Year”
Wikipedia’s exhaustive entry on the life and career of Albert Einstein (tinyurl.com/e9zvk) is an outstanding place to learn more about the iconic physicist.
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 tinyurl.com/yoklvg.
1906, Mars and Its Canals
Lowell’s Mars and Its Canals is available at tinyurl.com/4lr2fql.
1908, Tunguska Explosion
Artist and planetary scientist W.K. Hartmann has put together a fascinating account of eyewitness stories and artistic impressions about the Tunguska event at tinyurl.com/95pjc2t.
1908, Cepheid Variables and Standard Candles
Johnson, G., Miss Leavitt’s Stars: The Untold Story of the Woman Who Discovered How to Measure the Universe (New York: W. W. Norton, 2005).
A fun online applet, “Stellar Evolution and the H-R Diagram,” can be used to track the evolution of stars of different mass along and eventually off the main sequence: tinyurl.com/b35942.
1918, Size of the Milky Way
For details about the 1920 “Great Debate” between Harlow Shapley and his fellow American astronomer Heber Curtis (1872–1942) about the size of the universe, see tinyurl.com/9afp4fn.
1920, “Centaur” Asteroids
An up-to-date list of all known Centaurs and other “scattered-disk objects” is compiled by the IAU’s Minor Planet Center at tinyurl.com/99w9mrp.
1924, Eddington’s Mass-Luminosity Relation
Arthur Eddington’s 1926 book, The Internal Constitution of the Stars (Cambridge, UK: Cambridge Univ. Press), became an instant astronomy classroom staple and 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 from tinyurl.com/9tha5jc.
1927, The Milky Way Rotates
Astronomer A. Ghez’s Galactic Center Group hosts a wonderfully illustrated summary of views of our galaxy’s center at different wavelengths: tinyurl.com/9etp5wj.
1929, Hubble’s Law
Osterbrock, D.E., J.A. Gwinn, and R.S. Brashear, “Edwin Hubble and the Expanding Universe” (Scientific American vol 269, 84–89, July 1993).
1930, Discovery of Pluto
Tombaugh, C., “The Search for the Ninth Planet, Pluto” (Astronomical Society of the Pacific Leaflets, July 1946): tinyurl.com/8redhe8.
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 online as “My Brother Karl Jansky and His Discovery of Radio Waves from Beyond the Earth” at tinyurl.com/rrst4.
1932, The 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: tinyurl.com/99tcy9w.
1933, Neutron Stars
Details about the Hubble Space Telescope’s 1997 identification of a lone neutron star, “Hubble Sees a Neutron Star Alone in Space,” are at tinyurl.com/cstllk2.
1933, Dark Matter
N.D. Tyson and S. Soter provide some more details about the “irascible character” Fritz Zwicky in their profile at tinyurl.com/c45z6l3.
1936, Elliptical Galaxies
Edwin Hubble’s classic 1936 book, The Realm of the Nebulae (New Haven, CT: Yale Univ. Press), is based on a series of lectures that he gave at Yale in 1935 on his observations and interpretations of “island universes.”
1939, Nuclear Fusion
In his essay on the history of stellar nuclear fusion, “How the Sun Shines” (tinyurl.com/bocbkj4), astronomer J. 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, and other articles and documents about the early space program, appear in a volume edited by space historian J. Logsdon: Exploring the Unknown: Selected Documents in the History of the U.S. Civil Space Program (tinyurl.com/bruoxsd).
1948, Miranda
Planetary scientist P. Schenk has created some spectacular movies and views of the dramatic and weird topography on tiny Miranda: tinyurl.com/cr9cm3g.
1955, Jupiter’s Magnetic Field
See L. Garcia’s article on the Radio Jove website: tinyurl.com/csy4rch.
1956, Neutrino Astronomy
Gelmini, G.B., A. Kusenko, and T.J. Weile, “Through Neutrino Eyes: Ghostly Particles Become Astronomical Tools” (Scientific American, May 2010).
1957, Sputnik 1
For an entertaining glimpse of the America shocked by Sputnik and then spurred on to reach the Moon, check out H. Hickam’s Rocket Boys (New York: Delacorte Press, 1998) and the related 1999 film October Sky. (Universal Pictures).
1958, Earth’s Radiation Belts
More details about the phenomenally successful Explorer small satellite program (with 93 launches between 1958 and 2012) can be found at tinyurl.com/qp34s.
1958, NASA and the Deep Space Network
For details on NASA space science missions being tracked by the DSN, see tinyurl.com/5ucc4c and tinyurl.com/7ebsjx3.
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, as on Earth, the lit side and the dark side are constantly changing. At full Moon is the far side also the dark side; at new Moon, the near side becomes the dark side. Check out P. Plait’s explanation at tinyurl.com/ya4vf3w.
1959, Spiral Galaxies
Spiral galaxy and dark matter researcher V. Rubin is profiled in the Astronomical Society of the Pacific’s “Women in Astronomy” website: tinyurl.com/6e8r54.
1960, SETI
Kaplan, F., “An Alien Concept” (Nature vol. 461, 345–346, Sep. 17, 2009).
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 yurisnight.net.
1963, Arecibo Radio Telescope
Arecibo Observatory: tinyurl.com/9roxj3j.
1963, Quasars
An introduction to Hubble Space Telescope imaging and spectroscopy of quasars and their host galaxies can be found at tinyurl.com/8qtve6j.
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, 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 N.D. Tyson’s 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 world of black holes, wormholes, and other extreme physics concepts.
1966, Venera 3 Reaches Venus
Mitchell, D.P.: tinyurl.com/3nud9.
1967, Pulsars
Max Planck Institute for Gravitational Physics Einstein Online: tinyurl.com/8rqoc6u.
1967, Study of Extremophiles
T. Brock’s call for expanding the search for habitable environments on Earth was published in “Life at High Temperatures” (Science vol. 158, Nov. 1967, pp. 1012–1019).
1969, First on the Moon
Apollo Lunar Surface Journal: tinyurl.com/2bmqcq.
1969, Second on the Moon
Not much has been published about the Soviet Union’s failed human lunar exploration program. A summary of the Soviet efforts is available from space-history researcher M. Lindroos at tinyurl.com/8j2nj4q.
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. They describe their pioneering work at tinyurl.com/ydlehwe.
1970, Organic Molecules in Murchison Meteorite
Rosenthal, A.M., “Murchison’s Amino Acids: Tainted Evidence?” (Astrobiology, February 12, 2003): tinyurl.com/9ha432o.
1970, Venera 7 Lands on Venus
The National Space Science Data Center maintains a chronological list of Venus space exploration missions at tinyurl.com/8taqj9x.
1970, Lunar Robotic Sample Return
The NASA Lunar Reconnaissance Orbiter Camera team has made a priority of taking photos of “anthropogenic targets” such as the Luna, Surveyor, and Apollo landers; see images and details at tinyurl.com/8gotnwy.
1971, Fra Mauro Formation
Chaiken, A., A Man on the Moon: The Voyages of the Apollo Astronauts (New York: Penguin, 1998).
1971, First Mars Orbiters
Hartmann, W.K. and O. Raper, The New Mars: The Discoveries of Mariner 9 (NASA Special Publication 337, 1974).
1971, Roving on the Moon
Historical documents and technical schematics about the Apollo lunar rovers can be found in A Brief History of the Lunar Roving Vehicle (tinyurl.com/8nxezlh) and “The Lunar Roving Vehicle—Historical Perspective” (tinyurl.com/997dad8).
1972, Lunar Highlands
A spectacular series of virtual-reality animated panoramas of all the Apollo landing sites can be explored online at moonpans.com/vr/.
1972, Last on the Moon
See Wikipedia’s “Apollo program” web page at tinyurl.com/ynrjsz.
1973, Gamma-Ray Bursts
The original 1973 Astrophysical Journal paper announcing the discovery of GRBs, “Observations of Gamma-Ray Bursts of Cosmic Origin” by R.W. Klebesadel, I.B. Strong, and R.A. Olson, is online at tinyurl.com/9dhw9ot.
1973, Pioneer 10 at Jupiter
Follow the progress of the five NASA spacecraft on their way out of our solar system at tinyurl.com/8jlw3sm.
1976, Vikings on Mars
M. Carr’s beautifully illustrated The Surface of Mars (New Haven, CT: Yale Univ. Press, 1981) was a definitive summary of Martian geology up until the mid-1990s.
1977, Voyager “Grand Tour” Begins
For more details of the history and results of the Voyager missions, see my book The Interstellar Age (Dutton, 2015). Also, for more details about the Golden Record carried by Voyager 1 and 2, and the plaque carried by Pioneer 10 and 11, see C. Sagan’s Murmurs of Earth: The Voyager Interstellar Record (Ballantine, 1978). Also, follow the five NASA spacecraft on their way out of our solar system at tinyurl.com/8jlw3sm.
1977, Uranian Rings Discovered
Elliot, J. and R. Kerr, Rings: Discoveries from Galileo to Voyager (Cambridge, MA: MIT Press, 1987).
1978, 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 tinyurl.com/3uuj6t.
1979, Active Volcanoes on Io
R. Lopes and M. Carroll, Alien Volcanoes (Baltimore: Johns Hopkins Univ. Press, 2008).
1979, Jovian Rings
NASA’s Planetary Rings Node: pds-rings.seti.org.
1979, An Ocean on Europa?
Greenberg, R.J., Europa: The Ocean Moon (New York: Springer, 2005).
1979, Gravitational Lensing
Wikipedia’s “Gravitational lens” page at tinyurl.com/ola3h contains visualizations and animations that further explain the concept.
1979, Pioneer 11 at Saturn
NASA Special Publication 349 (1977), called Pioneer Odyssey, is a richly illustrated history of the Pioneer 10 and 11 projects: tinyurl.com/9lnp9ex.
1980, Cosmos: A Personal Voyage
Joining the Planetary Society (www.planetary.org), a nonprofit, public space-advocacy and education organization founded by C. Sagan, B. Murray, and L. Friedman in 1980, is a great way to directly participate in planetary and space exploration.
1980, 1981, Voyager Saturn Encounters
Pyne, S., 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: tinyurl.com/ygcz243.
1982, Rings Around Neptune
The current scholarly bible for the latest information on ring science is L. Esposito’s Planetary Rings (New York: Cambridge Univ. Press, 2006).
1984, Circumstellar Disks
Circumstellar Disk Learning Site: tinyurl.com/94879ma.
1986, 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. Download the survey’s report from tinyurl.com/3j8qcjb.
1987, Supernova 1987A
A spectacular time-lapse movie of so-called “light echoes” from Supernova 1987A between 1996 and 2002 is posted at tinyurl.com/9x8zuu6.
1988, Light Pollution
Learn more about the International Dark-Sky Association (and join!) at www.darksky.org.
1989, Voyager 2 at Neptune
The 1995 Univ. of Arizona Space Science Series book Neptune and Triton (D.P. Cruikshank, ed.) will likely remain an authoritative source on the Neptune system for a long time, as no new missions to the eighth planet are planned in the near future.
1989, Walls of Galaxies
Astronomer S.D. Landy introduces the concept of large-scale cosmic structures (including walls of galaxies) in “Mapping the Universe” (Scientific American, June 1999).
The Hubble Site (hubblesite.org) is a one-stop Internet shop for an amazing collection of information, stories, and pictures of the cosmos.
1990, Venus Mapped by Magellan
D. Grinspoon, who worked closely with Magellan Venus mission data, presents a fun account of Earth’s “twin” planet in Venus Revealed: A New Look Below the Clouds of Our Mysterious Twin Planet (New York: Basic Books, 1998).
1992, Mapping the Cosmic Microwave Background
Two leading COBE scientists, J. Mather and G. Smoot, received the 2006 Nobel Prize in Physics for helping to create a new era of precision observational cosmology using space-based missions.
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 tinyurl.com/39qusq for updates and details.
1992, Kuiper Belt Objects
The IAU’s Minor Planet Center is now tracking more than 1,250 trans-Neptunian objects in the Kuiper belt: tinyurl.com/9zxhsbz.
1992, Asteroids Can Have Moons
Finding a moon around an asteroid allows astronomers to determine the mass and density of the asteroid (using Kepler’s laws), which 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 historical and modern, at tinyurl.com/cnfuo4p.
1994, Comet SL-9 Slams into Jupiter
Spencer, J. and J. Mitton, The Great Comet Crash: The Collision of Comet Shoemaker-Levy 9 and Jupiter (New York: Cambridge Univ. 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. For details, see J. Bryner’s
“Wild Weather: Iron Rain on Failed Stars” at tinyurl.com/bn2q4jg.
1995, Planets Around Other Suns
Extrasolar Planets Encyclopaedia’s “Interactive Extra-solar Planets Catalog,” tinyurl.com/32bozw.
1995, Galileo Orbits Jupiter
Meltzer, M., Mission to Jupiter: A History of the Galileo Project (NASA Special Publication 4231, 2007): tinyurl.com/3gfnqge.
1996, Life on Mars?
National Space Science Data Center: tinyurl.com/6gjhsug.
1997, “Great Comet” Hale-Bopp
G.W. Kronk’s “Cometography”: tinyurl.com/8q6scg5.
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 Earth. See tinyurl.com/3rnenrp for a list of the naming themes used on all solar system bodies studied thus 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 planetary scientist J. Maki and the Mars Pathfinder team at tinyurl.com/976hyys.
1997, Mars Global Surveyor
The team that built and operated MGS Mars Orbiter Camera (MOC) created a spectacular collection of greatest-hits photos at tinyurl.com/8ezruqa.
1998, International Space Station
An animation showing the assembly sequence for the ISS between 1998 and 2011 can be found at tinyurl.com/d4plha.
1998, Dark Energy
See tinyurl.com/yv7q7d at the Hubble Site and the April 2009 Scientific American article “Does Dark Energy Really Exist?” by T. Clifton and P.G. Ferreira.
1999, Torino Impact Hazard Scale
More details about the Torino Impact Hazard Scale and the more recent Palermo Technical Impact Hazard Scale can be found at tinyurl.com/kwt3tg and tinyurl.com/94lg6dx, respectively.
1999, Chandra X-ray Observatory
Chandra X-ray Observatory Center: tinyurl.com/j84ul.
2000, An Ocean on Ganymede?
To me, Ganymede is a planet—larger than Mercury; differentiated into core, mantle, and crust; with a deep ocean and magnetic field—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. See tinyurl.com/7nbred7 for details.
2000, NEAR at Eros
National Space Science Data Center: tinyurl.com/cpvjrkv.
2001, Solar Neutrino Problem
An interesting history of neutrinos and the 1970–2002 astronomical detective story known as the “solar neutrino problem” is A.B. McDonald, J.R. Klein, and D.L. Wark’s “Solving the Solar Neutrino Problem” (Scientific American, April 2003).
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 and the oldest white dwarfs, as well as 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 J.C. Villanueva at tinyurl.com/97qw7mu.
2001, Genesis Catches Solar Wind
Burnett, D. and the Genesis Science Team, “Solar Composition from the Genesis Discovery mission” (Proceedings of the National Academy of Sciences, May 9, 2011): tinyurl.com/8lck3ra.
2003, Spitzer Space Telescope
Spitzer Web page at NASA’s Jet Propulsion Laboratory: tinyurl.com/44ys3.
2004, Spirit and Opportunity on Mars
My coffee table book Postcards from Mars (New York: Dutton, 2006) and my stereo-viewer book Mars 3-D (New York: Sterling, 2008) showcase the stories and photographic highlights from the Spirit and Opportunity rover missions.
2004–2017, Cassini Explores Saturn
Dougherty, M.K., L.W. Esposito, and S.M. Krimigis, eds., Saturn from Cassini-Huygens (New York: Springer, 2009).
2004, Stardust Encounters Wild-2
The December 15, 2006, issue of Science magazine presents the first detailed analysis of the chemistry and mineralogy of the Stardust samples.
2005, Deep Impact: Tempel-1
A collection of animations of the Deep Impact projectile’s crash into Tempel-1 is posted at tinyurl.com/8fsh7qx.
2005, Huygens Lands on Titan
Lorenz, R. and C. Sotin, “The Moon That Would Be a Planet,” (Scientific American vol. 302, 36–43, Mar. 2010).
2005, Hayabusa at Itokawa
Planetary Science Research Discoveries: tinyurl.com/8wxxq3x.
2006, Demotion of Pluto
The new IAU definition of “planet” is described in detail at tinyurl.com/qfrdxc, along with a discussion of the ensuing debate and controversy.
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 tinyurl.com/424vjmk.
2009, Kepler Mission
Kepler mission home page at NASA’s Ames Research Center: kepler.nasa.gov.
2010, SOFIA
SOFIA Science Center: sofia.usra.edu.
2010, Rosetta Flies by 21 Lutetia
Planetary Society blogger Emily Lakdawalla describes the details of her mosaic comparing Lutetia with the other asteroids and comets visited by spacecraft at tinyurl.com/csjulym.
2010, Comet Hartley-2
Details regarding analysis of Deep Impact and observations of Hartley-2 are continually updated at tinyurl.com/2ebtgxm.
2011, MESSENGER at Mercury
MESSENGER mission home page: messenger.jhuapl.edu.
2011, Dawn at Vesta
See my articles “Dawn’s Early Light: A Vesta Fiesta!” and “Protoplanet Closeup” in the November 2011 and September 2012 issues of Sky & Telescope for details.
2011, ALMA
Almaobservatory.org provides history, technical details, and the latest scientific results from the Atacama Large Millimeter Array facility.
2012, Mars Science Laboratory Curiosity Rover
Photos and movies of the Curiosity rover being built and tested, a time-lapse movie of the rover’s successful “sky crane” landing on Mars in August 2012, and the latest scientific results can be viewed from the mission’s main website: tinyurl.com/8h94w65.
2013, Chelyabinsk Fireball
For up-to-date information on the latest atmospheric impacts from comets and asteroids, including large fireballs, visit the fireballs page at NASA’s Center for Near-Earth Object Studies, at cneos.jpl.nasa.gov/fireballs/.
2015, LightSail-1
For details on the history of the LightSail-1 project, as well as plans and progress on LightSail-2, visit the Planetary Society’s LightSail project website at www.planetary.org/explore/projects/lightsail-solar-sailing/.
2015, Dawn at Ceres
For the latest and greatest images and other details about NASA’s Dawn mission to Vesta and Ceres, see the project’s official website at dawn.jpl.nasa.gov.
2015, Pluto Revealed!
New Horizons team website: pluto.jhuapl.edu.
2016, Juno at Jupiter
The official NASA Juno mission website, at www.nasa.gov/mission_pages/juno/, is loaded with the latest images and other details.
2016, ExoMars Trace Gas Orbiter
The European Space Agency maintains a detailed website with lots of background and details about the ExoMars Trace Gas Orbiter mission at http://exploration.esa.int/mars/46475-trace-gas-orbiter/.
2016, Gravitational Waves
A great collection of free downloadable Scientific American articles about the discovery of gravitational waves can be found at https://www.scientificamerican.com/report/the-discovery-of-gravitational-waves/.
2017, North American Solar Eclipse
Eclipse scientist F. Espenak keeps a detailed, updated set of web pages on upcoming solar and lunar eclipses and planetary transits at tinyurl.com/6cqw2c.
2017, Planets Around TRAPPIST-1
The “official” TRAPPIST-1 system website, at www.trappist.one, is a great one-stop shop for background, details, and new discoveries about the seven terrestrial planets recently found there.
2018, InSight to Mars
The latest information on NASA’s InSight lander mission to Mars can be found on the official website at insight.jpl.nasa.gov.
2019, James Webb Space Telescope
Gardner, J.P. and colleagues, Space Science Reviews (vol. 123, pp. 485–606, 2006): tinyurl.com/d7elwth.
2020, Start of Mars Sample Return
NASA’s official website for background and details about the Mars 2020 rover mission can be found at mars.jpl.nasa.gov/mars2020.
~2022, Europa Clipper
Lots of background and details about Europa and the 2022 Europa Clipper mission can be found at www.nasa.gov/europa.
2022, Jupiter Icy Moons Explorer
The European Space Agency’s official Jupiter Icy Moons Explorer website is at http://sci.esa.int/juice/.
~2025?, WFIRST
NASA’s Goddard Space Flight Center hosts the official website of the Wide-Field Infrared Survey Telescope mission, at wfirst.gsfc.nasa.gov.
2029, Apophis Near Miss
Apophis’s 2036 close approach to Earth depends on 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, which cannot be perfectly modeled in the computer.
~2035–2050, First Humans on Mars?
There are no insurmountable technical or engineering challenges to starting a human mission to Mars. The major obstacle appears to be the lack of sufficient government funding.
2050?, Breakthrough Starshot
To learn about all the Breakthrough Initiatives (“Listen,” “Watch,” “Message,” and “Starshot”), visit the Breakthrough website at breakthroughinitiatives.org.
~100 Million, Sagittarius Dwarf Galaxy Collision
Reich, E.S., “How Does Your Galaxy Grow?” (New Scientist vol 2717, July 17, 2009).
~1 Billion, Earth’s Oceans Evaporate
Kasting, J. and colleagues, “Earth’s Oceans Destined to Leave in Billion Years”: tinyurl.com/8t28g6x.
~3–5 Billion, 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 tinyurl.com/2mfudk.
~5–7 Billion, End of the Sun
Kaler, J.B., Stars (New York: Scientific American Library, 1992).
~1014, Last of the Stars
Ideas about the end of the so-called stelliferous era of star formation vary; see T. Darnell’s “The Decay of Heaven” (tinyurl.com/8r4na6n).
How Will the Universe End?
If you’ve never contemplated the end of time as a potential tourist destination, see D. Adams’s The Restaurant at the End of the Universe, originally published in 1980—after reviewing The Hitchhiker’s Guide to the Galaxy, first published in 1979.