A comet is making an appearance in the western sky this week, which observers in the St. Louis area might be able to enjoy once the weather breaks.
Known by the name of PANSTARRS, the comet was discovered over a year and a half ago, on June 6, 2011, by the 1.8-meter Pan-STARRS 1 telescope on Haleakala in Hawaii. Within a week, astronomers knew this comet could be something special, because of the brightness it was exhibiting despite being beyond the orbit of the planet Jupiter.
Although the comet was first visually spotted in the Northern Hemisphere on March 28, 2012, by an amateur astronomer in Spain, the comet began heading southward on August 4, 2012. It became temporarily lost in the sun's glare after October 7 and when it reappeared from twilight on November 27, it was only visible to observers in the Southern Hemisphere.
The comet reappeared in the skies of the Northern Hemisphere just a few nights ago. It was then located very low over the western horizon after sunset. Because the comet was closest to Earth on March 5 and closest to the Sun on March 10, it is at its brightest right now.
From my vantage point an hour south of St. Louis, I was lucky enough to spot the comet with binoculars about 20 minutes after sunset on the night of March 10. The initial appearance was star-like, but, within 15 minutes, I noted a slight fuzziness around the edges. I realized that I was seeing the central condensation of the comet, which is the bright core. Unfortunately, clouds moving eastward across Missouri, blocked the comet from view before I was able to see any additional details.
The St. Louis weather looks like it will give us a chance to see the comet on Wednesday night, although potential observers might watch the sky on Tuesday for a possible break in the clouds around the time of sunset. The comet's position with respect to the sun improves as the week progresses, with the comet being almost directly above the sun between Wednesday and Friday nights.
Although there have been reports of the comet being seen with the naked eye, I would recommend a good pair of binoculars to start searching the sky above where the sun dipped below the horizon, starting about 20 minutes after sunset. Binoculars will reveal the bright central condensation fairly easily. As it gets darker, a diffuse, cloudy feature will appear to surround the condensation and this is called the coma. As it continues to get darker, an extension will appear pointing generally upwards from the horizon and this will be the comet's tail.
Although astronomical observations typically require dark skies, that is not the case with this comet, as it will take a few weeks for it to exit twilight and become visible in a dark sky. By that time, it will have considerably faded. What is required is a fairly unobstructed view of the western horizon, which could simply mean looking down a westward directed street or going to a park, such as Francis Park in South City.
The last time PANSTARRS came thought the inner solar system was about 100 million years ago, when the dinosaurs were still roaming our planet. I wonder who or what will see it when it returns in another 100 million years?