M104, Humidity and Observing the Deep-Sky

Although I have known this for many years, It really hit home this spring when we had some really dry air over us. A few weeks ago we had a rather dry air mass pass over us and I could see stars that I don’t usually get to see. I know that air with humidity in the 30% to 40% range is not very dry for some places but here in North Carolina, where the normal summer time readings are in the 70% to 80% range, it was very dry for us. It was wonderful observing from home with such low humidity readings where I could easily see the Messier galaxies and many NGC galaxies.

In contrast to the low humidity, this past Monday I was out observing with much higher humidity readings. With the humidity at a still low 63%, I tried to find many of the galaxies that I had observed only a week before, only to find that I could just detect the presence of those galaxies and no longer really see them. This was very disappointing, knowing that the humidity was only going up in the months ahead. 

What causes this to happen? Summers in the southeastern United States tend to be very humid and that humidity holds pollen and dust particles in the air. These particles and the moisture in the air tend to scatter the light pollution, that is so common today, making the sky appear brighter. The end result is that the summer sky is much brighter than in the winter months. This brightening of the sky makes it almost impossible to see faint objects or the fainter outer regions of galaxies. Only the brightest portions of the inner areas of galaxies may be seen. For example, I observed M104 in Virgo. This galaxy has a listed size of 9’x4′ but what I could see was only approximately 3’x1′ in size. Obviously I was only seeing the brighter inner core region of the galaxy. Here is a sketch of this portion of M104 as seen Monday night. I was suprised to see the dust lane at magnification of 200x.

NGC1662 & 2169 in Orion

Orion is the home of two of my favorite wintertime open clusters. With Orion setting in the western sky early in the evening now, I have been scrambling to see these clusters for the last time this winter. The first is NGC 1662, The Klingon Battle Cruiser cluster. If you, like me, were a fan of the original Star Trek TV series, then you remember how the Klingon Battle Cruiser looked. Sue French in her February 2005 Deep-Sky Wonders column has a picture of the battle cruiser superimposed on this sparse cluster, and the stars definitely look like the running lights on the cruiser. I have never seen this cluster as anything else since.  Even in my light polluted skies, I see in town a good dozen stars with my 4-inch TV102 refractor. Check it out if you haven’t yet.

The second cluster is the Thirty-Seven Cluster, NGC 2169. This is a wonderful little cluster, whose stars are divided into two groups of stars. From home in my light polluted skies, using a C-6 or a 6-inch SCT, I see 11 stars in the southeastern group and 7 stars in the northwestern group. All of these stars can be seen within an area about 6 arc minutes in diameter. These stars look like a mirror reversed 37 in my scope at a magnification of 150x. Here is a sketch I prepared last week of this cluster. 


Two more wonderful Asterisms?

Since I brought up asterisms, I thought I would share two of my favorite summer asterisms and what I found out about them.

If you are like me, every spring you enjoy that star hop from Corvus to M104, the Sombrero Galaxy. Who can forget that line of four stars from gamma Corvus (Gienah) that ends with three stars, which look like an arrowhead pointing at the little asterism known as the Stargate, STF 1659. That’s right, I only recently learned that this little asterism is actually a multiple star system that is contained in the Washington Double Star catalog. I will bet that you, like me, thought that this grouping of stars got its name from the TV series by the same name but it didn’t. It was given this name from the Buck Rogers TV series back in 1979.

This multiple star, STF 1659, is made up of two triangles of stars; one nested inside the other. These six stars range in magnitude from 6.6 to 10.8. It is interesting that the Virgo diamond, described below, is about the size of the little triangle nested in the larger triangle in the DSS image below.

This is my sketch of this wonderful asterism or multiple star system.

Continuing on with the line of stars and the Stargate asterism will take you shortly to another asterism that I have found out is also a multiple star system, STF 1664, known as the Jaws. Although this is part of a much larger asterism of a shark, the gaping mouth of the shark is known as the Jaws and looks almost like a small Sagitta pointing straight at the Sombrero Galaxy, M104. These stars range in magnitude from 8.5 to 12.3 and you can see how close to M104 they are in this DSS photo.

I can see both of these multiple star systems from home in my 10×50 binoculars as a fuzzy little knot of stars. If you are not careful you might think the Jaws is M104, but look carefully, M104 is fainter but visible in the binoculars too.

The Stargate, STF 1659, is located at R.A. 12h35m44s, Dec. -12d01m30s and The Jaws, STF 1664 is located at R.A. 12h38m20s, Dec. -11d31m01s

The Virgo Diamond, A Challenging Asterism

Who would have thought it? In the middle of galaxy season, there is a seldom observed small asterism that has been called “a stellar diamond in Virgo”. Jaakko Saloranta, an observer from Finland states that “what makes this asterism curious and stand out is the diamond or square-shape and its tiny size (50″).” The separation between the stars is – on average – only 30″.  Good seeing conditions and higher magnification is required to resolve the four main components into individual stars. Seeing the 5th star on a less than average night, may require a  telescope with a larger aperture than the typical backyard telescope.

As reported in the May 1993 issue of Sky and Telescope Magazine, page 110, Noah Brosch of the Tel Aviv University, Israel, discusses his investigation of a newly discovered asterism in the December 1991 Monthly Notices of the Royal Astronomical Society. In summary he states that this is a system of five stars arranged in the form of a diamond. The stars have similar spectral types and radial velocities, indicating that the system is probably an evaporating small cluster in the Galactic halo.

Roger Ivester, an observer from North Carolina, said that on his first observation in his 10-inch Newtonian that he was surprised by how small the diamond appeared. Sue French, an observer from New York, states that with her 4-inch (105mm/610mm) the northern most star was easy but the other three are very faint at 122x. With her 10-inch Newtonian she could see all five stars at 213x. This year at the Winter Star Party, she could see all five stars with her 5-inch (130mm/819mm APO) at 164x. Several other people have seen all five stars with larger instruments.

Have I got you interested yet? This is a great challenge object that is a very nice break in the middle of galaxy season. With small telescopes this asterism will require dark skies with good seeing and good transparency. To help you I have prepared a sketch of this asterism from available information. It is located between Gamma (Porrima) and Eta (Zaniah) Virginis at R.A. = 12h 32.8m and Dec. = -00d 42m. The brightest star in the group is the 10.7 magnitude star TYC 4948-53-1.

and below is a photograph of the Diamond by Don Olive. This is , of course, not to be taken for the Great Diamond of Virgo. The four stars that form the Diamond of Virgo are Cor Caroli (in Canes Venatici), Denebola (in Leo), Spica (in Virgo), and Arcturus (in Bootes).