DSO – Page 2 – Pear Tree Observatory

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.

With the PTO’s science camera still in the shop, I drug out my 15 year old Nikon D50. Although it doesn’t have the dynamic range or resolution of the science camera it sure is easier to create a full color image.

The Orion nebula is one of the nearest star forming regions to the Sun and based on recent analysis, is home to 700+ stars in various stages of formation. The mighty Hubble space telescope has also recorded more than 150 infant solar systems in the stellar nursery. Technically, the young systems are known as protoplanetary disks AKA proplyds.

Orion Nebula (M 42) [F:15x30s]

The nebula is just at the limit of naked eye visibility. It is the middle object in the ‘sword’ that hangs from the hunter’s three star belt.

If you have ever wondered what a bazillion dollars buys you in the Astronomy world, here is an example. Yesterday’s Astronomy Picture of the Day (APOD) is a shot of M 96 (AKA NGC 3368) taken by the HST (Hubble Space Telescope). Below is the same galaxy taken in 2013 by the PTO deep space camera through my 10″ scope.

M 96 [C:9x300s]

You can definitely see the prominent dust lanes visible in the HST image although in mine you cannot positively identify them as such. They could be gaps between spiral arms. In the HST shot you can also see what appear to be either background galaxies or satellite galaxies on the upper right and middle left of the main target as well as a bright young cluster of blue stars on the galaxy’s left. All three are visible in the PTO shot but they all appear as small blurry spots.

I am doing some wide field experimenting with my ancient and honored Nikon D50 DSLR. The images below were taken through a 18-55mm zoom lens, set at a focal length of 55mm. This generates a FOV of 25.7°x17.0° with each pixel representing 30.5″ of arc. The camera is mounted on a GEM (Losmandy G-11) to prevent long exposures smearing the stars.

I haven’t come up with a way to flat field these images yet which is why there are some dark splotches visible. These are known as dust donuts and are the result of dust or other material somewhere in the light path. Additionally, the camera was manually focused resulting in a soft look to the stars.

The first image is centered between the open star clusters Pleiades and Hyades. Most of the image is in the constellation Taurus. The bright star at the bottom right is the star Aldebaran. The ‘V’ shaped Hyades, the lower cluster, forms the head of the Bull with Aldebaran representing the eye. The orientation of this image is north to the left and east down and is slightly cropped to remove the tree line along the southern edge.

Taurus [M:17x60s] (mouse over for labels.)

The second image contains most of the constellation Orion. Visible in the ‘sword’ is the Orion nebula (M 42;NGC 1976) and just at the limit of visibility is a hint of the Flame nebula (NGC 2024) next to Alnitak. Curiously, M 42 is not identified in the annotated image. The orientation of this image is north up and east to the left.

Orion [M:30x60s] (mouse over for labels)

My next steps will be to try some different techniques to eliminate what appears to be some external reflections in the images and to add in the color. I like the scale of the image when the lens is set to 55mm and the optical distortion at the edge of the FOV is not as extreme as when the lens is set to a faster focal length. I think I will add this configuration to my list. I will also look for an affordable 50-55mm non-zoom lens.

The target of this image is NGC 2149, a small reflection nebula in the constellation Monoceros (the Unicorn). It is quite near the constellation Orion and often gets overlooked due to the more flamboyant objects in “The Hunter”. I routinely exclude images taken of deep sky objects when a satellite intrudes into the photo. The brightness of the intruder skews the desired object’s post processing. I must admit however, last night I intentionally chose NGC 2149 because of the impending satellite pass. The guilty party this time was the Hubble Space Telescope.

I decided to attempt the exposure knowing full well the Moon’s brightness would cause a strong gradient in the exposures. After all, the Moon was only a few hours from entering the Earth’s shadow and the resultant total lunar eclipse. Hubble would cross my FOV in just over one second. It takes 10 seconds to download an image from my camera, so in order to not miss the pass I set the exposure to 300 seconds and started it a couple of minutes before the expected arrival. I then joined family members in the front yard to watch the flyby. Hubble silently glided west to east and near the point where it disappeared, it did its best imitation of an Iridium flare. The scope’s solar arrays were at just the right angle to reflect the Sun’s light right back at us. It then faded as its orbit took it into the Earth’s shadow.

Luckily, the satellite’s orbital elements used to predict its path were right on and the 300 second exposure showed the very bright telescope streaking through the image. I then took additional images of the nebula to increase its brightness a little. The result is a stack of one 300 second image and 25 sixty second images.

Pear Tree Observatory
temp:	43℉ (6℃)
humidity:	78%
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 03:58
updated(Z):	24-11-21 09:58

Pear Tree Observatory

Beehive cluster (M 44)

The Great Orion Nebula (M 42)

PTO vs. HST

Wide Field Experimentation

NGC 2149 and friend