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Thankful for Comets

Gazing upon the night sky during this holiday season may bring a glimpse of a comet that could put on an impressive display. Through Thanksgiving week, comet ISON (known as C/2012 S1 in more formal lingo) will head toward the Sun. If it survives the pass around the Sun without disintegrating, the comet may end up visible with the naked eye in through late December

In my lifetime, only a handful of comets have grown bright enough to be detected without a telescope. The three most popular (at least as I remember) occurred during the 1990s.

My Top Three Comets

As impressive as ISON might appear, it won’t match the brilliance of comet Hyakutake(a.k.a. the Great Comet of 1996). I remember seeing this comet with the naked eye in March 1996, while working at the Fred Lawrence Whipple Observatory in southern Arizona. With clear, dark skies, I saw Hyakutake’s tail extending almost 90° across the starry expanse.

Image credit: Wikimedia/Creative Commons/E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria (

Following closely on the tail (no pun intended) of Hyakutake, Hale-Bopp (the Great Comet of 1997) first appeared in the sky in May 1996. Its close passage to the Sun later that year made it difficult to see, but after showing up brilliantly again in January 1997, Hale-Bopp remained visible for the rest of the year.


Image credit: Wikimedia/Creative Commons/Michael K. Fairbanks

From a scientific perspective, the most interesting comet I’ve encountered is Shoemaker-Levy 9. Although this comet never brightened enough to be seen without a telescope, it made history in July 1994 when scientists observed its impact with Jupiter—making it the first collision between two large solar system bodies ever witnessed. On a previous trip close to Jupiter, Shoemaker-Levy 9 was ripped into 20+ pieces ranging in sizes of up to two kilometers in diameter. If a fragment of this size were to collide with Earth, the impact would release far more energy than the simultaneous detonation of the world’s entire nuclear arsenal!

Reasons to Be Thankful for Comets

Comets and asteroids impact our planet regularly—at least on geological timescales. While these impacts can cause great destruction (such as the impact that wiped out the dinosaurs), they also bring water and other important materials to Earth. Some collisions, like those during the Late Heavy Bombardment, helped prepare Earth for the next advance in its capacity to support life. One of the largest collisions in Earth’s history ultimately led to the formation of the Moon.

So, not only do comets provide spectacular displays in the heavens, they also play an important role in Earth’s habitability. As we (hopefully) glimpse comet ISON in the night sky, let’s thank God for so carefully crafting this planet as our home.