Now that the days are getting warmer and our entertainment options are more limited, this might be the perfect time to sit in isolation under the stars and contemplate your place in the universe. And if that sounds too metaphysical, you could just take in some old-fashioned stargazing.
Another topic for contemplation is the idea that comets are like cats – both have tails and are hard to predict. There are typically several comets per year that can be seen with binoculars. Most are tiny dots that are almost indistinguishable from faint stars unless you use a telescope to provide additional magnification. Rarely are comets visible to the naked eye. When they are, it is worth the effort to see them.
Comets are made up of dust and ice and spend most of their time in the outer, colder parts of the solar system, far away from the sun. If a comet’s orbit brings it near the sun, the ice will evaporate, sending a vapor cloud out into space. This cloud of outgassed material surrounding the head is called the coma. When we see a comet, it is the coma, and maybe a tail, that we are seeing.
The dense head of any comet is typically very dark and might only be a few kilometers across, but the bright coma could be many thousands of kilometers across, and the tail could easily be millions of kilometers long.
The tail forms when the solar wind blows lightweight evaporated material away from the sun. So a comet’s tail is always pointing away from the sun, even when the comet itself is heading away from the sun. That would be one big difference between comets and cats, as I have never seen a cat running tail first.
I looked over my previous columns to find references to comets that were visible with either the naked eye or binoculars and there have been many. The most spectacular was probably Comet ISON in 2013. It was a relatively easy, but ho-hum target in binoculars when it suddenly brightened by a factor of 10 and was briefly visible to the naked eye. Also that year were comets 2/P Encke and C/2013 R1 Lovejoy. Then in 2015, Comet C/2014 Q2 Lovejoy (another with that name) was dimly visible. Comet C/2013 US10 Catalina, Comet 45P/Honda-Mrkos-Pajdusakova, Comet C-2017/O1 (ASASSN1) and Comet 46P/Wirtanen were some of the others.
This month, Comet C/2019 Y4 (ATLAS) is the comet to watch. It is circumpolar, which means it is close enough to the north star to be visible all night. Right now, it is in the constellation Camelopardalis. The name means camel-leopard, or something that is like a camel, but has spots. In English, we know that as a giraffe. Comet C/2019 Y4 is another comet that has been unexpectedly brightening and could be putting on quite a show by the end of the month.
The reason it is so hard to predict the brightness of any newly discovered comet is simply lack of information about its internal structure and composition. As the comet approaches the sun, the heat of the sun is digging into the comet. Sometimes, a new pocket of ice is exposed and the comet gets much brighter. But like mining for gold, you don’t know what you will hit until you dig. And sometimes you come up empty.
This monthVenus is in Taurus, near the Pleiades and the Hyades. It is setting late in the evening, as are the rest of the winter constellations around Orion.
Just after 1 a.m., the summer Milky Way is rising, giving us a preview of the summer evening sky.
This is a good time of year to see the zodiacal light on a moonless night right after dusk. This is light reflecting off interplanetary dust in the solar system. It is most easily visible in the evening near the vernal equinox.
April is often a month when I discuss upcoming public star parties, but I am afraid that discussion will need to wait for another time.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory. Reach him at firstname.lastname@example.org.