The Pleiades, M45

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Jared Willson Senior Member • Posts: 1,447
The Pleiades, M45
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About the Object

Normally, when you see an open cluster such as the Pleiades surrounded by a blue reflection nebula you assume that you are looking at extremely young stars that have not yet dispersed the cloud of gas and dust from which they were formed. That is not the case with the Pleiades. Based on fitting the stars in the cluster to HR diagrams, stellar evolution models suggest the Pleiades are somewhere between 75 and 150 million years old, far too old for the original dust and gas from their formation to have survived. The cluster just happens to be moving through a particular dusty section of the interstellar medium, resulting in the bright reflection nebula. The cluster is thought to contain at least 1,000 stars with a combined mass of roughly 800 suns.

The Pleiades are an extremely prominent star cluster in the constellation Taurus, and thus have had names in many different cultures. In greek mythology, the Pleiades were the seven daughters of the titan Atlas and the sea nymph Pleione. The name of the cluster supposedly derives from Pleione, though it is more likely that the name derives from the greek word "plein" which means "to sail" as the appearance of the Pleiades was used to mark the beginning of the safe sailing season in the Mediterranean. The cluster is also known as "Subaru" in Japanese culture, hence the star filled emblem for the modern car company.

About the Image

The image is comprised of just under eleven hours worth of one minute exposures and is a two-panel mosaic since the entire cluster would not fit well in the field of view of the telescope. Separate exposures were taken through a clear filter (luminance) as well as red, green, and blue filters to build up a true color image. The color was balanced by comparing stars against a G2V database of "white" stars--those similar to our Sun.

The telescope used was my 305mm aperture Riccardi-Honders reflector with a 1,124mm focal length, yielding a focal ratio of f/3.7. The mount used was an AP1100GTO AE which has absolute encoders that allow for extremely precise tracking even without guiding.

The telescope is housed in a remote shared observatory in Rowe, New Mexico which provides very dark skies and good seeing conditions above much of the atmosphere's water vapor at close to 7,400ft altitude. I can operate the telescope remotely from my home in Oakland, California.

The camera used was a QHY600 monochrome, cooled CMOS camera running at -10*C. The cooling reduces thermal noise in the image. The frames were all calibrated using master dark, flat, and bias frames to ensure the best possible starting data. All image calibration and post processing was performed in PixInsight.

M45, The Pleiades

A higher resolution version of the image can be found here.

In addition to the main structure of the cluster, you can find lots of distant background galaxies in the image. Here is an annotated version of the picture that labels the main stars of the Pleiades as well as all the individual galaxies visible.

Annotated Pleiades

Since it is hard to read the small text, just know that each of the teal labels represent a background galaxy or cluster of galaxies. The benefit of having dark skies...

Thanks for looking!

- Jared

 Jared Willson's gear list:Jared Willson's gear list
Leica Q2 Hasselblad X1D II 50C Leica SL2 Leica SL 90-280mm F2.8–4 Hasselblad XCD 30mm F3.5 +8 more
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