Me, Myself and Messier: M45

This scribbing was originally published in the now-defunct Astronomy Wise. It was part of a series that was written but not published before the magazine folder. This page is draft.

The Pleaides, or Seven Sisters as they are popularly known, are arguably the best known object in the Messier Catalogue. They are certainly the brightest and can be seen easily without any optical aid from an urban location. They were certainly well-known before the invention of the telescope. They are in the constellation of Taurus but, when low in the east are best found at the feet of Perseus. Except for pre-dawn early risers in early summer, they are visible from just after midnight in August to late April dusk. One of the challenges is to see how many stars you can count without using a telescope or binoculars. The record is 19 and I managed 12 in my younger years when my eyesight was much better. Most people will see six or eight, depending on their eyesight and the prevailing conditions. It is thought that one of the “seven” sisters has faded over the years making it equal in brightness to the eighth member.
Some of the brighter members of the catalogue are within the reach of simple astrophotography – just holding a camera to an eyepiece and snapping. The fainter ones need more sophisticated tools and techniques that involve a mount that can track an object across the sky and use long exposure times.

The photo above shows the constellation of Taurus in November. The V shape star pattern is known as the Hyades and is an open star cluster that appears larger than the Pleaides, which are to the right. In fact they are roughly the same size but the Pleaides are much further away. Many have said that the Pleaides look nothing like a comet but fuzzy conditions and bad quality optics might give a different impression. The photo suggests that there are six main members plus three or four fainter members. An advertisement for some seriously large binoculars suggests that there are 103 members.

The figure above suggests around 40 stars and is quite typical of what one might see when using a small widefield telescope, such as a Startravel 80 or similar sized binoculars. It was taken using a Startravel 80 with a DSLR camera attached. Amateur astronomers describe the Pleiades are about 2 degrees in diameter or 4 times the diameter of the full moon. However, recent research suggests that there are a lot of outlying stars once thought to be background stars and brown dwarves have also been seen. The full cluster extent seems to be about five degrees. It is an object that I like to visit with binoculars frequently but on a clear night I will sometimes try to photograph it. It will show up in widefield constellation shots, such as the photo of Taurus, above, taken with a DSLR or compact digital camera with a few seconds exposure. Before buying a DSLR, I used to photograph the Pleiades through binoculars or hold a camera to a telescope eyepiece at low magnification. However, the figure above is near the limit of what can be achieved using simple methods.
I have only seen it once and never photographed it but there is a nebula associated with the Pleaides. Research suggests that the star cluster and nebula just happen to be in the same place, do not share a common origin and will pass through each other and separate. The Pleaides are a suitable target for astronomers starting off with photography or those who are on a limited budget. My early attempts were taken through a Startravel 80 and a hand-held compact digital camera. I have even taken some shots through binoculars and finderscopes. However, a good imaging set-up does absolutely no harm and there are many excellent images of the Pleaides on the internet.
The key to getting a good view of the Pleaides is to use an instrument with a wide field of view. My binoculars have a field of view of around 4 degrees. I can also obtain a similar field of view with my Startravel 80 telescope with a 32mm Plossl eyepiece. Another technique I use is adding an Antares focal reducer to the imaging path. This enables me to get the whole object into the field of view using my Skywatcher Skymax 127 Maksutov and 32mm Plossl eyepiece. Although I use a light pollution reduction filter for viewing many Messier objects with this set-up, it is not helpful for viewing the Pleaides, as it reduces the brightness of the cluster and does not aid clarity. Being an open star cluster, it is not as affected by light pollution as galaxies, nebulae and globular star clusters.
To sum up, the Pleiades are the easiest of all the Messier objects to view and photograph. They can be enjoyed through small binoculars and large telescopes, although it is better to use a wide field of view. When organising outreach events, they are a great object to give audiences the wow factor. They are also an excellent subject for photography, even if your equipment is limited.
At the time of writing, I was experimenting with using an advanced DSLR on the Pleiades and simimar objects. However, I had not got any results that were as good as the one here. I was hoping for another crack before it disappeared until August.

Further Information

Click here to see details of my book on the Messier objects
Click here to see the Wikipedia entry for M45
Click here to see the SEDS Messier database entry for M45

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