The sky, for the most part, is predictable; the Sun rises and sets, the Moon goes through its phases, and the constellations appear pretty much the same on the day that you are born as the day you die. The appearance of a great comet, however, offers a wonderful exception; though many are on periodic orbits, many others enter our inner solar system unannounced, putting on dazzling displays. A bright comet may even be visible in the daytime. The recent discovery of comet C/2012 S1 (ISON) has raised some speculation that we may just be in for such an event in late 2013, with some scientists predicting that comet could be as bright as the full Moon. Here’s a compilation of 10 remarkable comets from the past few hundred years.
10. Comet Lovejoy
In November 2011, Australian observer Terry Lovejoy discovered a faint +13th magnitude object. Comet C/2011 W3 Lovejoy was a Kreutz sun grazer, one of a handful seen each year. It surprised astronomers, however, when it survived its fiery plunge just 87,000 miles above the Sun’s surface (about a third the distance between the Earth and Moon) to become a fine morning object for southern hemisphere observers, similar to Ikeya-Seki in the 1960s. Comet Lovejoy was visible in the daytime, and astronauts even photographed it from the International Space Station. (A quick primer: the brightness of an astronomical object is described as its magnitude. The lower the number, the brighter the object, and one step in magnitude is equal to 2.512 times in brightness.)
9. Comet McNaught
The first bright comet of the 21st century, Comet C/2006 P1 McNaught reached a brilliance of several times that of Venus at magnitude -5.5 and was termed the Great Comet of 2007. One of the brightest comets in the past century, McNaught sported a brilliant fan-shaped tail and was seen by millions worldwide. If you missed it on the first pass, you’re out of luck — McNaught is on an extremely long period orbit, and won’t return to the inner solar system for another 92,600 years.
8. Comets Hale-Bopp and Hyakutake
The 1990s were a great decade for comets. In 1994, the astronomical world watched in awe as fragments of Comet ShoemakerLevy-9 impacted Jupiter, causing tremendous damage to the giant planet. Then in 1995, observers Alan Hale and Thomas Bopp independently discovered what was to become one of the most observed comets of the 20th century. What immediately excited astronomers was its relatively large discovery distance; beyond the orbit of Jupiter, Comet C/1995 O1 Hale-Bopp had to be an intrinsically large and bright object. Like Halley’s Comet in 1910, Hale-Bopp was “scooped” during its anticipated 1997 passage by the sudden appearance of Comet C/1996 B2 Hyakutake in early 1996. Both served as fine studies in the appearance of bright comets; one small and close up, and one large and bright, but farther away. Hale-Bopp displayed a fine twin ion and dust tail; Hyakutake passed just over 9 million miles from Earth and sported a tail that stretched halfway to the zenith. Both became circumpolar objects in the night sky and were above the horizon for observers based in mid-to-high northern latitudes for the entire night.
7. Lexell’s Comet
In 1770, Comet D/1770 L1 Lexell made the closest recorded passage by a comet to our planet of all time, passing only 1.4 million miles from Earth. This is less than six times the Earth-Moon distance, and the comet sported a coma over four times the size of a full Moon as seen from Earth. The closest approach to Earth by a comet in the 20th century was Comet C/1983 H1 IRAS-Araki-Alcock, which passed 2.9 million miles from us in 1983.
6. The Eclipse Comet of 1948
A surprise greeted observers during the total solar eclipse of Nov. 1, 1948, when a bright comet was sighted next to the Sun. Formally titled C/1948 V1, the Eclipse Comet of 1948 was one of the last to be discovered in this accidental fashion. The eclipse comet was briefly visible to the naked eye for the remainder of the year.
5. The Great January Comet of 1910
Many who anticipated the passage of Halley’s Comet actually saw this comet (officially designated C/1910 A1) several months earlier. First noticed by South African diamond miners in the early morning of Jan. 12, 1910, this comet went on to make a fine display for Northern Hemisphere observers, and boost the “Halley hype” in the minds of many, including the media.
4. The Great March Comet of 1843
The 19th century was a great era for comets, and one of the most memorable was comet C/1843 D1, dubbed the Great March Comet. Another Kreutz group sun grazer, the Great March Comet displayed a tremendous fan-shaped tail over two astronomical units in length (1 AU equals the distance between the Earth and Sun). By the way, the dust tails of comets are swept back via pressure from the solar wind and actually precede comets as they head back out of the solar system.
3. The Great September Comet of 1882
A bright daytime comet, Comet C/1882 R1 was first spotted by several witnesses in the Southern Hemisphere and went on to become one of the great comets of the 19th century. The comet was also notable for producing a bright anti-tail, a sharp, spikey-looking feature that appears to be pointing sunward. Interestingly, this comet transited the Sun on Sept. 17, 1882, and astronomer W.H. Finlay famously tracked the comet almost right up to the solar disk — a feat we don’t recommend trying to duplicate.
2. The Great Comet of 1680
One of the brightest comets of the 17th century, the Great Comet of 1680 is also sometimes referred to as Kirch’s Comet. The subject of many paintings of the era, Isaac Newton used the orbit of the comet as a study in the verification of Kepler’s laws of motion. There is some thought that the aforementioned Comet ISON, which is set to visit the inner solar system in late 2013, may be related to the Great Comet of 1680.
1. Halley’s Comet
The best known of all periodic comets, Halley’s Comet visits the inner solar system every 75-76 years. The comet was the first to have its orbit calculated by Sir Edmond Halley, who predicted the return of the great comet in 1759. Famously, American author Mark Twain was born in 1835 during the passage of Halley’s Comet and predicted he would “expect to go out with it,” which he promptly did in 1910. A fleet of international space probes visited the comet in 1986, and it will next grace Earth’s skies in 2061.
One More: Comet Kohoutek
Comets can be fickle beasts, often defying predictions and failing to perform. A fine cautionary tale is that of C/1973 E1 Comet Kohoutek, discovered in 1973. Astronomers projected it would become the “Comet of the Century” and the media trumpeted those claims. Kohoutek partially disintegrated and failed to live up to expectations. Ironically, the experience from Kohoutek caused the media to largely ignore a fine comet less than two years later, Comet C/1975 V1 West.