Saturday, October 3, 2020

An old Standby

In these days of Covid-19, getting together with others to have a look at the night sky is an exercise of don'ts: don't get too close to each other, don't touch or look through the telescope, don't come without a mask, etc. On-line meetings are substituting for the in-person ones. My wife and I are practicing voluntary self-isolation (we are old enough to make this necessary). That means that I'm confined to observing the sky from our home. 
We live in a highly light-polluted and horizon-limited area. The smoke from the wildfires in the U.S. has added to the lack of visibility of the stars. There were just a couple of acceptable evenings which led me to look for one of my favorite objects in the sky: The Whirlpool Galaxy not far from the end of the Big Dipper's handle. In a dark sky, M51 can be seen in larger binoculars as a small, diffuse patch of light.

I used my 15x50 Canon stabilized binoculars to try and see it. I did not detect it at all. The gray sky here made it an impossibility.  In earlier years M51 was easy to see from our house; high-rises, new and under construction, now limit our horizon and add much light pollution.

I decided to get my "M51 fix" by posting an image I took a couple of years ago by connecting my computer to to use one of their remotely accessible telescopes and take a picture; below is the result:

 Messier 51 
Image taken through the wide-field, 17 inch remote-control telescope located at the Institute of Astrophysics of the Canary Islands. 

 Some history (from Wikipedia):

"What later became known as the Whirlpool Galaxy was discovered on October 13, 1773, by Charles Messier while hunting for objects that could confuse comet hunters, and was designated in Messier's catalogue as M51. Its companion galaxy, NGC 5195, was discovered in 1781 by Pierre M├ęchain, although it was not known whether it was interacting or merely another galaxy passing at a distance. In 1845, William Parsons, 3rd Earl of Rosse, employing a 72-inch (1.8 m) reflecting telescope at Birr Castle, Ireland, found that the Whirlpool possessed a spiral structure, the first "nebula" to be known to have one. These "spiral nebulae" were not recognized as galaxies until Edwin Hubble was able to observe Cepheid variables in some of these spiral nebulae, which provided evidence that they were so far away that they must be entirely separate galaxies even though they are seen close together. The advent of radio astronomy and subsequent radio images of M51 unequivocally demonstrated that the Whirlpool and its companion galaxy are indeed interacting."

There are still some uncertainties regarding M 51. For instance, the distance of it is variously quoted as 31 million light years (NASA), Wikipedia says about 23 million, states 19 to 27 million light years. A location chart is shown above. A dark sky will allow for M 51 to be seen in 10x50 binoculars as a faint patch of light. An 8" (200mm) telescope will begin to show its spiral structure.

Messier 51 is circumpolar, so it is accessible for most of the year. At this time of year, the Big Dipper skirts the northern horizon through the night. M51 is therefore moves along above the northern horizon as well. Give it a try under a dark sky anyway. Its position will improve as we progress through winter and into next year.