November 21, 2009

M46

This is an open cluster appearing in the constellation of Puppis, which in the fall and winter sky appears low on the southern horizon to the east of Orion. The constellation is named for the deck of the ship used by Jason and the Argonauts. M46 is a relatively large cluster with around 500 member stars. Astronomers estimate the cluster's age at about 300 million years. It is about 5,500 light years away.

In addition to its fine appearance when viewed with binoculars or a small telescope, M46 appears to contain a surprise - a small planetary nebula, NGC 2438, which appears as small colored disk at the cluster's edge. Astronomers consider this to be more appearance than actual association since the nebula appears to be moving at a different speed than the cluster, and since the cluster's member stars are too young to have gone nova (the death throes of older stars, which produces planetary nebulae). It is most likely that the nebula lies in front of M46 and simply appears to be part of it.

The image below is a crop of the preceeding image, showing NGC 2438 near the upper middle of the frame, at the top edge of the cluster's core.

The above images were comprised of five, 300-second subexposures - a total exposure time of 25 minutes.

M44

This a large open cluster in the constellation Cancer, also known as the Praesepe (Latin for Manger) or Beehive Cluster. M44 was first noted by Greek and Roman astronomers; Galileo viewed it with his homemade telescope as early as 1609; more than 150 years later Charles Messier added it to his catalog.

M44 has about a thousand member stars, but its members have dispersed over a fairly large area over the eons. It is about 577 light years away and occupies an area larger than the full moon. The cluster is best viewed with binoculars or a telescope with low magnification and a wide field of view.

Four, 300-second subexposures were combined to create this 20 minute exposure.

M103

This small, arrow-shaped cluster in Casseopeia is a great jewel of the summer sky. I've imaged it before using the 6" Newtonian at f/5. However, I am experimenting with a barlow lens to increase the telescope's magnification by a factor of two, increasing the focal ratio to f/10. My purpose here is to better capture very small objects, like galaxies and certain planetary nebula. The image of M103 below was the first test of my new 2x barlow. Compare this image with my earlier image a few months back without the barlow.

This image, taken through the 2x barlow, is a stack of nine, 100-second images, for a total exposure of 15 minutes.