Each month I will describe sights of interest in the night skies of South Carolina. These sights will be broken down into four sections; what you can see with the naked eye, with binoculars, with a small refracting telescope, and with a Dobsonian reflector. The best time to view the night sky is at and around the times when the Moon is not visible, what is known as a New Moon; which will occur this month on March 27th. For March, your best viewing nights will be from March 18th to the 31st. The Star chart below is set for Florence, SC on March 15th at 9 pm. Note: A table of contents for earlier columns is located in the March 2016 column.
Short Period Comet Hunting:
It has been several years since we have seen a readily visible comet. When amateur astronomers get tired of waiting for a naked eye comet, they enjoy searching for small dim comets, using binoculars or a telescope. Most of these comets have a “P” designation in their name, which means they are a periodic comet. Periodic comets have a relative short orbital time around the Sun, ranging from a few years to a maximum of 200 years. There are almost 100 short period comets that orbit the Sun from 10 years to only a few years. This month, one such comet, is 41P/Tuttle–Giacobini–Kresák; note the letter ”P” followed by the names of the three people who discovered it. Below is a telescopic view of this comet taken on February 25, 2017.
The first time it was observed was in 1858 and it has an orbital time around the Sun of 5.4 years. This month, is the closest approach it has ever made to Earth; 13 million miles. However, it still may not be a bright or easy to spot comet. The reason that most of the short period comets are seldom seen as naked eye objects is directly related to their short orbits. When any comet swings around the Sun, called perihelion, large amounts of its surface gases are blown away. The ejection, or burning off of this surface material produces the large bright comet tails that we see when a new comet enters into our solar system. However, these short period comets may have passed near the Sun hundreds or thousands of times. Most of the surface debris that forms the bright long tails have long ago been depleted. So these comets tend to be dim and usually have no tails, or only a small tail.
The best time to start looking for this comet is around March 22nd. From this time until the 25th it will pass through the bowl of the Big Dipper. Therefore, you will have no problem aiming your binoculars. At this time of year, the Big Dipper will appear upside down. The comet will enter from above and into the bottom of the Dipper’s bowl on March 22nd and exit the bowl on March 25th. See the images below.
First note that these images are from a computer astronomy software, and the computer default always shows a comet having a tail. The positions of the comets are accurate, but the visual representations are not. The red circle shows the field of view for a 7 X 50 mm binocular. The two bright stars to the left are Merak on the top and Dubhe on the bottom. The unknown factor is how bright the comet will appear based on the darkness of your viewing location. If the comet is bright enough for binocular viewing, then you will be able to follow it each night as it moves away from the Dipper’s bowl. The closest approach of the comet to the Earth will be the last day of the month through the first days of April. Again, depending on the darkness of your viewing site at this time the comet may become faintly visible to the naked eye.
What may you expect to see? Most likely you will see the comet as a small fuzzy ball, which will make it easy to distinguish it from the nearby stars. As it gets nearer to the Sun it may begin to form a small tail. In the worst case, it may be so dim that you may have trouble distinguishing it from the nearby stars. If you have any doubt that the tiny diffuse object is the comet, then check the next night to see if it has changed its position.
What I have described in the paragraph above is probably an accurate description of your viewing experience of comet 41P/Tuttle–Giacobini–Kresák this month. However, there is another reason that you should try to locate the comet. Think of a comet as an onion, and each pass around the Sun peels off one layer of debris and gases. However, these “layers” are not uniform. Using the onion analogy, look at the image below.
Layers one and two may have a small amount of tail forming gases and debris, but layer three may contain huge amounts of tail forming material. This irregularity would result in a significant brightening of the comet and tail formation when the comet passes around the Sun and “layer three” is exposed.
This irregular brightening of comets is not normal for most comets. However, comet 41P/Tuttle–Giacobini–Kresák has a history of these outbursts. The most recent explosive outburst of a comet occurred in November 2007. ScienceSouth telescopes were at Lynches River Park, and the public viewed the impressive outburst of Comet Holmes which became larger than our Sun!
Personally I would be happy just to see the comet this month, and learn how to pronounce its name.
Naked Eye Sights: Say goodbye to Orion as it sets in the west.
Binocular Sights (7 to 10 power): View comet 41P/Tuttle–Giacobini–Kresák.
Telescope Sights (60-100mm): View comet 41P/Tuttle–Giacobini–Kresák.
Dobsonian telescope (6 -8 inch): View comet 41P/Tuttle–Giacobini–Kresák.
See you next month!