DECEMBER 6, 1997: Jim Scotti with the Spacewatch program in Arizona discovers the Apollo-type asteroid now known as (35396) 1997 XF11. This asteroid created a major stir the following year when orbital calculations indicated a very close approach to Earth would be occurring in October 2028, and even though subsequent calculations with more data moved the “miss distance” out much farther, the process itself forced a re-thinking of how potential future close encounters are approached. The story is discussed in a previous “Special Topics” presentation.
DECEMBER 6, 2020: JAXA’s Hayabusa2 mission returns to Earth with its collection of soil samples that it collected from the near-Earth asteroid (162173) Ryugu, from which it departed 13 months ago. After releasing a capsule containing these samples that is then expected to be retrieved from the Woomera Test Range in South Australia, Haybusa2 will depart Earth’s vicinity for an eventual flyby of the Apollo-type asteroid (98943) 2001 CC21 in 2026. The Hayabusa2 mission is discussed in last week’s “Special Topics” presentation.
DECEMBER 7, 1968: NASA’s Orbiting Astronomical Observatory 2 (OAO-2) satellite, the first successful space telescope, is launched from Cape Canaveral, Florida. In January 1970 OAO-2 made the first observations of a comet from space – Comet Tago-Sato-Kosaka 1969g, a previous “Comet of the Week” and the first comet I ever observed – and detected the Lyman-alpha hydrogen cloud that is now known to accompany almost all comets passing through the inner solar system.
DECEMBER 7, 2020: The large main-belt asteroid (16) Psyche will be at opposition. It is currently traveling westward through Taurus and is close to 9th magnitude. Psyche is primarily metallic in composition and potentially important in the mining of asteroids, and is also the destination of NASA’s Psyche mission currently scheduled for launch in August 2022. These aspects of (16) Psyche are discussed in previous “Special Topics” presentations.
DECEMBER 8, 2251 B.C.: According to calculations by Zdenek Sekanina and Rainer Kracht, Comet Hale-Bopp C/1995 O1 passes through perihelion (during its previous return) at a heliocentric distance of 0.907 AU. The comet would have been well placed for observation, passing 0.65 AU from Earth and potentially becoming as bright as magnitude -2. This may have been the comet’s first visit to the inner solar system from the Oort Cloud, and it would have passed within 0.01 AU of Jupiter on the way in and captured into the shorter-period orbit that it occupies today.
DECEMBER 8, 1845: The German amateur astronomer Karl Hencke discovers the main-belt asteroid now known as (5) Astraea. This was the first asteroid to be discovered in almost four decades, and its discovery soon led to many other asteroids being discovered, and eventually to the realization that our solar system contains a large population of such objects. The story of the discovery of the asteroid belt is the subject of the Week 1 “Special Topics” presentation.
DECEMBER 8, 2018: Images of the main-belt asteroid (6478) Gault taken by the ATLAS program in Hawaii begin to show that it is accompanied by a comet-like tail. This feature would develop significantly over the next few weeks, and meanwhile, examination of old images of Gault revealed that it has exhibited this tail as far back as September 2013. This tail activity makes Gault an “active asteroid,” the subject of this week’s “Special Topics” presentation. Gault itself is a previous “Comet of the Week.”
DECEMBER 8, 2019: The interstellar Comet 2I/Borisov passes through perihelion at a heliocentric distance of 2.007 AU. This was the first confirmed example of a comet from interstellar space passing through the solar system, and it is a previous “Comet of the Week.”
DECEMBER 8, 2020: The nucleus of the unusual Comet 29P/Schwassmann-Wachmann 1 – a recent “Comet of the Week,” and currently in a state of outburst – is predicted to occult a 14th-magnitude star in Aries. The predicted path of the occultation crosses western Russian, southern Sweden, and Scotland.
DECEMBER 9, 1805: The comet now known as Comet 3D/Biela passes 0.037 AU from Earth, becoming an easy naked-eye object of 4th magnitude or brighter in the process. Comet Biela, a previous “Comet of the Week,” appears to have completely disintegrated during the mid-19th Century.
DECEMBER 9, 2023: Comet 1P/Halley will be at aphelion, at a heliocentric distance of 35.143 AU, after which it will begin heading back into the inner solar system for its next perihelion passage in July 2061. Comet Halley is the subject of a previous “Special Topics” presentation, and its most recent return in 1986 is a previous “Comet of the Week.”
DECEMBER 11, 2010: Steve Larson with the Catalina Sky Survey in Arizona reports that the main-belt asteroid (596) Scheila is a magnitude brighter than expected and is accompanied by a coma. This coma was apparently the result of an impact by a smaller asteroid, and in the meantime has caused Scheila to be considered as an “active asteroid,” the subject of this week’s “Special Topics” presentation.
DECEMBER 12, 1970: NASA’s Orbiting Geophysical Observatory 5 (OGO-5) satellite detects a Lyman-alpha hydrogen cloud around Comet 2P/Encke, the first detection of such a feature around a short-period comet. Comet Encke, which returned earlier this year, is a previous “Comet of the Week,” and Lyman-alpha hydrogen clouds are discussed in previous “Ice and Stone 2020” presentations.
DECEMBER 12, 1992: Comet 109P/Swift-Tuttle 1992t, the parent comet of the Perseid meteor shower, passes through perihelion at a heliocentric distance of 0.958 AU. Comet Swift-Tuttle is last week’s “Comet of the Week.”
DECEMBER 12, 2003: A team of astronomers led by Matthew Povich and John Raymond publishes their paper describing observations of Comet Kudo-Fujikawa C/2002 X5 and relating these to the likely existence of comets in other planetary systems. These observations are discussed in more detail in a previous “Special Topics” presentation on exocomets.
DECEMBER 12, 2020: The recently-discovered Comet Erasmus C/2020 S3 will pass through perihelion at a heliocentric distance of 0.398 AU. Comet Erasmus had brightened to close to 6th magnitude by the time it disappeared into the dawn sky early this month, and will be located 11 degrees west of the sun during the total solar eclipse on December 14; it possibly may be bright enough to detect during totality. Solar eclipse comets are discussed in a previous “Special Topics” presentation.
DECEMBER 12, 2020: The main-belt asteroid (498) Tokio will occult the 4th-magnitude star Omicron Virginis. The predicted path of the occultation crosses southern Greenland, portions of the Norwegian and Barents Seas, the southern part of Yuzhny Island, and parts of central Siberia.
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