Next entry: Venus and Jupiter in the eastern sky, a spectecular sight!

Previous entry: Lunar eclipse october 28th

Deepsky observing with different instruments!

NGC 6633 and IC 4756
On the night of september 9th 2004 Leo (a fellow observer) and I observed with the 15x80 binoculars and Sky Window, 7x50 binoculars and the 10-inch Newton from Skywatcher. We started of with two fine open clusters NGC 6633 in Ophiuchus and IC 4756 in Serpens Cauda. These two big open clusters can be seen

in the same field of view of the 7x50. They are separated 3 degrees from each other. In the 15x80 only both the cluster cores fit in the 3.5 degree field of view. NGC 6633 has a diameter of 27’ and a visual magnitude of 4.6. In the 15x80 I see a bright star north-northwest of the cluster. I see some 20 to 25 stars of almost the same brightness in the direction northeast-southwest. In the centre of the cluster I can see a triangle of stars.

IC 4756 is much larger. Its diameter is 52’ and its visual magnitude is 4.6.  Through the 15x80 it seems be lie within a trapezium of brighter stars. I can see about 30 to 35 stars but there is also a glow of unresolved stars.

The map below should give you an idea of what you see through a 7 x 50 binocular (North is up. East is to the left). The limiting magnitude is about 9 to 9.5 and the big red circle represent a field of view of 6.1°. IC 4756 is on the left and NGC 6633 is on the right.

image
Credit and © Capella Soft, “SkyTools2”

M 39
Next on the list was M 39 in Cygnus. This open cluster has a diameter of 31’ and its visual magnitude is 4.6. It is very easy to spot. From Deneb, go about 9 degrees in east-northeastern direction, and you will see the triangular shape of M 39 immediately. In the centre of the triangle I could see a yellowish star. It is a very poor cluster. I counted only 12 to 15 stars.

M 31
From M 39 I turned to Andromeda, to find M 31. Through big binoculars you see the real size of M31. This galaxy is a binocular object! When I move the mirror from the Sky Window up and down, I really see the full size of 3 degrees. M 110 is also clearly visible as a small elongated smudge of light. M 32 is invisible. I could not detect any structure or details in M 31.

Double Cluster / Stock 2
This area is wonderful for observing with binoculars. With the 15x80 Stock 2 is an impressive sight. Its stars form the figure of a man with its arms and legs spread. You will recognize this asterism immediately, using big binoculars. Stock 2 is a large open cluster with a diameter of 1 degree. It is connected to the double cluster in Perseus by a 2 degree arc of stars that runs in the north-south direction. The double cluster looks stunning through any telescope or big binocular, even through the 15x80. The “western” cluster, NGC 869 is also called h Persei, the “eastern” cluster, NGC 884, is called Chi Persei. Both clusters have a diameter of 30’, the size of the full moon.

Interesting is that each of the double cluster components have a true diameter of 65 light-years, while Stock 2 has a true diameter of 18 light-years. But why does Stock 2 look much bigger than the components of the double cluster? That’s because of the different distances they lie away from us. The double cluster lies at a distance of 7200 to 7500 light years, while Stock 2 lies relatively nearby at a distance of 1050 light years. This area is interesting enough to revisit many times, with any kind of optical aid.

Alpha Persei moving cluster (Melotte 20 or Per OB3)
This is a deepsky object for 7x50 binoculars. The 3.5 degree wide open cluster is too big to fit into the 15x80. The small binoculars leave some room around Melotte 20, so it stands out very well from it’s surroundings. In the centre of the field of view I counted 30 to 35 stars. The age of the Alpha Persei moving cluster is estimated at 50 million years. It is thought that the Alpha Persei cluster is one of oldest Gould Belt objects, together with the Pleiades. The Gould Belt is a remnant ring of bright stars, star forming regions and remains of molecular clouds that is tilted about 20 degrees to the galactic plane.

NGC 7789
This big open cluster in Cassiopeia looks like a really bright patch of light through the 15x80. NGC 7789 has a diameter of 25’ and a visual magnitude of 6.7. I could not detect any stars or granulation. The brightest star has a visual magnitude of 10.7. With the 10-inch Skywatcher and a Zeiss zoom-eyepiece, NGC 7789 looked stunning. The whole field of view was filled with maybe 80 stars of equal brightness. At moments like these you wish that you had a 400-inch telescopesmile) Together with NGC 457 and Stock 2, NGC 7789 forms my favorite trio of star clusters in Cassiopeia.

NGC 752 (Collinder 33) and the Golf Putter
About 4 degrees south-southwest of the beautiful double star Gamma Andromedae lies another great binocular cluster, NGC 752. Together with an asterism called “the golf putter”, NGC 752 forms a great couple for observing with big binoculars. The golf putter can be is formed by a chain of bright stars that run from the northwest to the southeast. Three stars in the southeast form the end of the chain. To the east of the asterism lies NGC 752, which could be seen as the golf ball. In the 15x80 the 1.5 degree golf putter and NGC 752 look fantastic.

M 33
We ended the night with M 33 in Triangulum. With the Skywindow and the 15x80 binoculars, M33 is very easy to find. From Beta Andromedae move your binoculars to the south in the direction of the western tip of Triangulum. Keep looking very carefully if you see a really big smudge of light while moving south. Even in a light polluted sky M 33 is very easy to spot using binoculars. It is 67’x41’ in diameter. With the 15x80 I estimated its size around 30’. It is however impossible to see any structure or details in M 33 with binoculars from our light polluted backyard. This object again proves that some galaxies are great objects for binoculars.

Posted by Math on 10/30 at 02:01 AM
Deepsky log • (0) TrackbacksPermalink