Star gazing OR: Double stars in the big dipper
August 17th, 2009 | by Digvijay Lamba |
Tonight was my first night with an old Celestron C8* SCT telescope that I recently assembled. The scope is not in very good shape and it took me a little while to adjust to working with it. Thankfully, the motor drive works well so it can track stars. The biggest issue I have with the scope is that two different knobs need to be controlled to move the scope around, which is very irritating.
Anyways, I started out looking at the Big Dipper as Mizar and Alcor find an easy to find double. After using them to align my finder scope I moved to on to looking at double stars. I was observing from downtown San Jose with expectedly poor visibility and street lights visible all over the place.
Naked eye visibility was about 3 mag as I could see both the top stars (Beta and Gamma on the right) in Ursa Minor as well as Polaris. However, I could not see Megrez (the big dipper star that joins the arm with the cup, see below) which is a 3.3 mag star.
My 10×50 Binoculars do quite well in these conditions and I could easily see down to about 7.5 to 8 Mag with them. The finder scope (8×50) could do about 6..75 Mag so I used both to star hop. Though even reaching the first bright star was quite a lot of trouble in the rickety telescope.
Back to double stars! Mizar and Alcor form an easy to resolve visual double at the bend of the handle in the big dipper. They were visible even in my Binoculars. Harder to do split was Mizar itself which is actually a triple! But my puny scope easily split two of the stars Mizar A and Mizar B which have a 12 arc seconds distance.
The next set of double stars in the Big Dipper are near Alioth. Alioth itself almost looks like a double star with a much fainter very nearby star next to it about 1m 12s away. This is a very distinct visual as one of the stars looks much smaller than Alioth, which is the brightest star in the Big Dipper.
Right nex to Alioth are two other double stars. Together these form a “7″ shape with Alioth at the bend, this shape is visible in the image on the left. The upper left star is 78 Ursa Major which is a double with two stars at 4.9 and 7.75 Mags about 1.7s apart. Despite trying very hard I could not split these with my telescope even at a very high resolution.
The bottom of the “7″ shape has two stars, the lower of which is HIP 63143 and is also a double star. The two parts of this double are 3.3s apart with a magnitude of 5.45 and 7.7. The were barely resolved with my 6mm eyepiece at a resolution of about 300x and then too only if I looked hard.
Next, I moved to Megrez. M40 is a very faint double star right next to it. Look at another “7″ shape to the left of Megrez, not included Megrez itself. The right next to the star on the bend lies M40. Not visible in my finder or binoculars, I had to make a guess at it. After some effort I found M40 clearly split at 25x resolution and more. M40 is an optical double with two stars at 10.1 and 9.65 Mags about 54.85 seconds apart. These are really faint in my scope.
By this time the big dipper was falling below the horizon so I moved to the Hercules constellation for another couple of doubles before calling it quits. The easiest way to locate Hercules is the 3 star asterism including Pi Hercules at the top left of the box. You can’t miss it. Both stars next to Pi Hercules are actually double stars. The leftmost one is p hercules and the two components of this double are 3.9 s apart. The middle star is 69 hercules and is a double with two stars only 1.4s apart. Once again this I failed to split. It seems my telescope can split doubles about 3s or greater apart.
Of course, if you are in hercules the M13 is a must watch. Called the Great Globular Cluster is visible to the naked eye as a fuzzy star on a dark night. With a diameter of 145 light years, it is a huge globular cluster with hundreds of thousands of stars.
From the city however I’ll be lucky to resolve it at all. Surprisingly, I can detect a cottony fuzzy star in my binoculars though the finder scope comes up empty. After some effort I located it in my 25x viewfinder and as usual it is huge in size, nearly 20 arc minutes across. It takes up most of scopes view.
Unfortunately, it is too faint to resolve at higher magnifications so I have to be satisfied with a dim look that is nowhere near as clear as the picture on the right.
And with that I packed up the scope… a relatively successful night despite the bad scope!
Tags: Astronomy, Big Dipper, Double Stars, Night Sky, Observation Log, San Jose, Star Gazing, Telescope