Although the stars and constellations we see in April are a sure sign spring is here, we know better than that living in Wyoming. At least we get some clear nights between snow storms and the snow melts faster this time of year. The bright constellations of winter Canis Major, Orion, Gemini, Taurus and Auriga hover in the western sky. The bright stars Betelgeuse, Sirius and Procyon form the asterism known as the Winter Triangle. Overhead this month you’ll find Leo easily picked out by a backwards question mark we call the Sickle. The hindquarters of Leo the Lion is made up of three stars forming a triangle. The Big Dipper (part of Ursa Major) is north of Leo. If you follow the curve of the stars making the dipper’s handle you’ll run in to the bright star Arcturus, the brightest star in Bootes. If you continue that curve you’ll find Spica the brightest star in Virgo. To the west of the Sickle is the dim constellation of Cancer, if you point binoculars at those faint stars you’ll find a lovely cluster of stars known as M44 the Beehive Cluster. If you sweep your binoculars above the eastern end of Leo’s triangle you’ll find a large cluster of stars known as the Coma Cluster.
One of the most exciting things I find about astronomy and star gazing is knowing something spectacular or unusual can happen at anytime. Recently many astronomers were excitedly watching the red supergiant star Betelgeuse fade to an unprecedented magnitude and wondering if the massive star was about to go supernova. The odds of that happening in our lifetime is rather small, but it was thrilling to watch and speculate. Recent observations of Betelgeuse is slowly brightening again and astronomers speculate a large dust cloud is responsible for the star becoming less bright.
Some of the unexpected things we can see in the sky are brilliant meteors, meteor storms and a lovely planetary conjunction – especially when a crescent moon is nearby, northern lights and an occasional naked eye comet. Two of my most memorable moments were watching Saturn cross in front of a second magnitude star and seeing the star pop in and out of view of Saturn’s rings.
The other one was on a bitterly cold, snowy night when we propped my 4” telescope up in a snow drift and watched every 20 minutes or so as Comet Hyakutake was rounding the sun – you could see the comet’s tail switching direction as it was being blown away by the solar wind.
Predicting comets is not very easy or reliable, but there is hope we may have a naked eye comet in April or May. Comet McNaught was naked eye in 2006 but was only visible in the southern hemisphere at its brightest. In 1995 we had the brilliant Comet Hale Bopp and in 1995 we enjoyed the spectacular Comet Hyakutake; so in my opinion (or wishful thinking) we are due for another bright comet.
Comet Atlas (2019 Y4) was the last comet discovered in 2019. It was found by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Hawaii. The comet was shining at a dim 20th magnitude and 273 million miles from the Sun. Often when comets are discovered that far out they are unusually large or bright. Recent observations of Comet Atlas show the comet continues to brighten more rapidly than expected, which means if that rate continues, the comet could put on a spectacular show when it is closest to the Sun on May 31. The comet will actually come closer to the Sun than Mercury as it passes only 23.5 million miles from the Sun that day. If the current rate of brightening of Comet Atlas continues, it could be as bright as Venus and may even be visible in daylight.
Comet Atlas has an estimated 6025 year orbit, it last rounded the Sun in about 4000 BC, and will next appear around the year 8045. At its closest, the comet will be moving at 2 degrees per day through the sky in late May, about four times the apparent diameter of the Full Moon.
The best chance to see the comet is mid-May at dusk for northern hemisphere observers, as the comet heads towards its closest encounter with the Sun. Unfortunately at its brightest in late May and early June, the comet will be hugging the northeast horizon at sunrise and competing with the rising sun.
This comet’s orbit also happens to be similar to the Great Comet of 1844-1845 (C/1844 Y1), which reached first magnitude. Perhaps, the two are fragments of a larger comet that broke apart on one of its close encounters with the Sun.
I have to note many expected great comets have disappointed us when they failed to brighten as expected. Comets tend to be very erratic and unpredictable. Passing close to the Sun can cause comets to break apart, so there is a chance Comet Atlas completely fades away as it closes in on the Sun. A large cometary nucleus will continue to release large amounts of frozen gas as it nears the sun, but a smaller comet will crumble and fade away.
Comet Atlas is well placed for the Northern Hemisphere. Right now the comet is in Ursa Major; it will move in to Camelopardalis where it will stay through April. It may be naked eye by mid or late April, but we’ll have to wait and see.