Open Cluster – Pear Tree Observatory

I am still developing the procedures necessary to process one shot color (OSC) camera images. This is the first D90 image I have processed using the color information. The steps to process an OSC camera are totally different than the steps I use to produce color images taken by my science camera. The larger FOV also adds additional complexity. This image is 2.83° wide versus my science camera having an FOV of only 24′ (arc minutes). However, the increased area makes it much easier to image multiple objects without having to assemble a mosaic of smaller images.

This picture is centered on an object in the southern constellation Sagittarius: The Lagoon Nebula. Also known as M 8, it is a large emission nebula being energized by the open star cluster NGC 6530 that lies in it. Also easily visible towards the lower right is M 20 (The Trifid Nebula) containing both emission and reflection nebulae. The small concentration of stars at the upper left is the globular cluster NGC 6544.

Lagoon Nebula (M8) [F:10x120s]

Chart generated by Cartes du Ciel (CdC)

Chart courtesy of IAU/Sky&Telescope

The vertical yellow line that runs all the way through the CdC chart is the ecliptic. Since most asteroids orbit in the plane of the solar system, the image contains a lot of them. I counted 31 identified on the chart by small green dots, but due to the image scale and the asteroid’s magnitudes I couldn’t find any of them.

Both M 8 and M 20 are just visible with binoculars. Using the constellation chart, observe just above the spout of Sagittarius’ Tea Pot asterism (heavy green lines).

While waiting for Jupiter and Saturn to clear my tree line, I did some more testing with my wider FOV scope that has a simple DSLR mounted on it. I am still manually focusing the system but it doesn’t take too long to accomplish. The recently installed flattener corrects the distortion apparent in the stars at the corners of each image.

The target for tonight’s testing was Messier 11 (The Wild Duck Cluster). Legend has it the cluster was given its name by British Admiral William Henry Smyth (1788-1865). When describing the cluster, the Admiral, a very accomplished astronomer and avid hunter, commented the V-shaped group of stars looked like a flock of wild ducks.

Classified as an open star cluster, the flock is located in the constellation Scutum (The Shield). The constellation is right in the middle of the plane of the Milky Way and towards the center of the galaxy. That is fairly apparent by the sheer number of stars in the image. North is to the right putting M 11 right on the northern edge of the Scutum star cloud. The dark area towards the bottom right side of the image is not a lack of stars. It is a large area of dust and gas dense enough to block the light of more distant stars. Several of these areas were individually cataloged as dark nebulae by American astronomer E. E. Barnard, hence the B numbers on the matching chart.

Wild Duck Cluster (M 11) [M:11x120s]

As can be seen on the constellation chart, Scutum is in the southern sky located between Aquila and Sagittarius. The image and matching chart are rotated 90° to the constellation chart.

Chart generated by Cartes du Ciel

Chart courtesy of the IAU and Sky&Telescope

Once Jupiter and Saturn cleared the trees I switched over to planetary equipment and was able to get a couple of series of both planets before wispy clouds moved in from the south. As usual, the best Jupiter image was uploaded to NASA’s JunoCam web page for mission planning.

Jupiter [(V)TR:2506×0.74ms;TG:2501×1.1ms;TB:2505×1.7ms]

I have been testing a new optical configuration to give the PTO the ability to record larger FOV images. Mounting my Nikon D90 to a 80mm f/6 apochromatic telescope gives a 2.9°x 1.9° FOV image. The resulting 5.26 sq° image is 97% larger than the standard science image used for asteroid/comet analysis. The size of the camera chip is large enough though that significant distortion is visible at the extreme corners of the image. As you can see the stars are ‘stretched out’ with each pointing towards the center of the image. This is known as pincushion distortion. A field flattener will need to be added to correct this problem.

The test target is a fairly large open cluster. It lies in the center of the constellation Cancer and is known as the Beehive cluster. The current population count is about 1,000 stars although only the brightest form the naked eye object. This is one of the first objects observed by Galileo when he first turned a telescope to the sky. He counted 40 stars.

Beehive Cluster (M 44)
[M:4x60s]

The compressed display makes the image background much brighter than it should be. Click on the image for a larger more accurate view. This will also make the corner distortion easier to see.

NGC 6791 is an open star cluster in the constellation Lyra. Discovered in 1853, it is unusual in that there are three distinct populations of stars in the group. Along with a group of 8 billion year old normal stars there is a group of white dwarfs with a 6 billion year age and a group of white dwarfs with a 4 billion year age. This is contrary to the classic definition of open star clusters such that the stars of such a group are all born from the same molecular cloud and all have the same general age. Needless to say, this cluster has astronomers questioning their understanding of cluster formation and is heavily studied.

NGC 6791 was one of the few deep sky objects included in the field of view (FOV) of the Kepler spacecraft during its primary science mission.

(NGC 6791) [C: 56x60s]

Chart generated with Cartes du Ciel

The observatory upgrade proceeds, but the outside temperature has delayed cutting new floor panels. The current plan is to try again over the next couple of days. If the conditions don’t improve I will restore the previous floor/wiring configuration to bring the PTO back online as soon as possible and watch for the next favorable opportunity to resume the floor task. I am anxious to observe the shadow of minor planet (1424) Sundmania as it passes across the panhandle on the 12th of January.

In the meantime I am processing a backlog of imagery.

This image was taken on the 14th of December. NGC 2266 is a compact open cluster discovered by William Herschel in 1785 in the constellation of Gemini. It is relatively old for an open cluster and has an estimated age of 1 billion years. The cluster’s distance has been estimated as 2.6 kpc (8485 ly).

NGC 2266 [C:58x30s]

Chart generated with Cartes du Ciel

Pear Tree Observatory
temp:	50℉ (10℃)
humidity:	58%
wind (MPH):	From the NNW at 0
pressure:	30.1 inHg
station:	KFLVALPA4
hardware:	Davis Vantage Pro 2
software:	VWS V15.00
updated(L):	24-11-21 01:24
updated(Z):	24-11-21 07:24

Pear Tree Observatory

Lagoon Nebula and friends (14 Jun 2020)

Wild Ducks and Jupiter (11 Jun 2020)

Beehive cluster (M 44)

NGC 6791

NGC 2266