Astr111 Photography Projects, Fall 2009

M39- Open Cluster in Cygnus, Justin Dammons

M39 is an open cluster in the constellation Cygnus, discovered by Charles Messier in 1764. In the sky, it is situated around nine degrees east and north of Deneb (Alpha Cygni). It is about 950 light years away from Earth and 9.12 light years across. The cluster is estimated at being anywhere from 230 to 300 million years old. There is controversy surrounding who actually discovered M39. The astronomer LeGentil (who discovered M38 and other clusters), sometimes is credited with discovering M39, however there are different astronomers who state that this is "extremely doubtful". The constellation Cygnus, which is the Latinized Hellenic (Greek) word for swan, also includes the asterism Northern Cross, and it is one of the 88 modern constellations. In the constellation, M39 can be found in the left wing of the swan. It is visible in good condition by the naked eye, and the best time to view this constellation (and this open cluster) is in the northern summer and autumn.

In this image, there are a few number of bright stars (in the center of the picture, upwards of eight), but the middle of the cluster is where you can find the majority. It is important when looking at this image and picturing this open cluster that one realizes that the faint stars might or might not be a part of this cluster, that distance is hard to determine by first glance. This is because of the Milky Way galaxy and how we view this cluster (because we on Earth are apart of the Milky Way). All of the bright stars are included in the constellation Cygnus, however, none of them are prominent enough to be listed as important enough for the structure of Cygnus. The visual brightness of M39 is 4.6 mag, and the angular size is 43 arcminutes, the same size of the field of view. An interesting thing to note is that when you have a lower magnification, and you're able view the cluster in detail, a lot of the major stars (the bright ones) are grouped in pairs. You can view this in the picture above. To create the picture above a mosaic was used, which is taking four sets of pictures and piecing them together because the cluster is so wide, one picture really can't capture all of its glory. The mosaic includes the faint stars around the edges of the picture, and the brighter stars are in the middle.

References:
Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. Princeton University Press, Princeton.

Frommert, Hartmut and Kronberg, Christine. "M39." Students for the Exploration and Development of Space. <http://www.seds.org/messier//m/m039.html>

Arnett, Bill. "M 39." Nine Planets.<http://astro.nineplanets.org/dssm/m39.html>