Asterism and Open Cluster in Vulpecula

At magnitude 3.6, the Coathanger, also known as Brocchi's Cluster, is not difficult to see with the naked eye. Because it covers about 1 degree of sky, the best view is through binoculars, through which its distinctive shape can be readily seen (though it is upside down for Northern Hemisphere observers). It now seems fairly certain that this group is not a true cluster but simply a chance alignment of stars. This is because measurements based on parallax indicate that the distances of the 10 brightest stars vary from about 230 to over 2000 light years.

The dimmer and more distant open cluster NGC 6802 can be seen just to the right of the Coathanger in this image. NGC 6802 contains a few dozen stars in an elongated rectangular shape. It is about 5800 light years away.

Image details:  Exposure times of 30 minutes luminance and 18 minutes each of red, green and blue, taken with an SBIG 8300M imager and a Tokina 500 mm lens.

October 2017