November 28, 2009

IC 434 - The Horsehead Nebula

This is my second image of the Horsehead. My previous effort had a total exposure time of 50 minutes. The image below is comprised of 19, 300-second subexposures, which were combined for a total exposure time of one hour and thirty-five minutes.



M47

This open star cluster appears in the constellation Puppis, close enough to the cluster M46 (see post below) that the two can often be seen together in the same field of view through binoculars. M47 is smaller than M46, containing only about 50 stars and is estimated to be younger as well - about 78 million years old. It is also considerably closer than M46 at a distance of just 1,600 light years.

Six, 300-second subexposures were combined to create this 30 minute exposure.

M41

Appearing just 4 degrees south of Sirius, the brightest star in the night sky, M41 is a large, bright cluster of about 100 stars, including several red giants. The cluster has been estimated at 240 million years in age and is about 2,300 light years away. It makes an excellent target for small telescopes and binoculars.

Two, 300-second images were combined for a total exposure time of 10 minutes.

NGC 2903

As dawn approaches, the winter sky begins to give way to the constellations of Spring, now rising just before the sun. NGC 2903 is a fine barred-spiral galaxy, seen at a tilt, in the western part of the constellation Leo. Discovered by William Herschel in 1784 - who thought it to be a nebula - it remains something of a mystery why Charles Messier never included it in his famed catalog. The galaxy is bright enough to have easily been within the capability of his telescopes, and he noted at least four other galaxies in Leo (M65, 66, 95 & 96). Modern astronomers have estimated NGC 2903 to be 20.5 million light years distant.

This image, cropped to enhance the galaxy, is composed of ten, 300-second images, for a total exposure time of 50 minutes.

M106

This spiral galaxy appears in Ursa Major and is located about 25 million light years away. It appears in a particularly rich field of galaxies, and has been identified by some astronomers of the Ursa Major Cloud - a large group of galaxies. I have annotated the image below to identify the several dimmer galaxies that appear in the field of view.

This image was composed by combining nine, 300-second images for a total exposure time of 45 minutes.

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.

November 17, 2009

M35

This spectacular open cluster appears in the constellation Gemini, named for the twins Castor and Pollux from Greek mythology. The cluster can be found easily with binoculars or a small telescope by sweeping near the three "foot stars," Eta, Mu and Nu Geminorum. This cluster was first noted by the French astronomer Phillippe Loys de Cheseaux as early as 1745, and was added to Messier's catalog about 20 years later. Astronomers estimate M35 to be about 110 million years old; the cluster contains between 200 and 500 stars and is about 2,800 light years away.

The image below captures not only M35, but also the smaller cluster NGC 2158 (lower middle of frame), a significantly more compact cluster thought to be about a million years old and about 16,000 light years distant.

This image is comprised of six, 180-second subexposures, for a total exposure time of 18 minutes.

November 1, 2009

The Clusters of Auriga

When the sky is clear, but the moon is almost full, its argent glow drowning out the faint gossamer nebulae, it's time to capture some of the Fall sky's better star clusters. Three of the best happen to appear in the constellation of Auriga, the Charioteer, which rises high into the sky by midnight. Auriga's brightest star (Alpha Aurigae) is Cappella, which is almost impossible to overlook in the night sky, moon or no moon. The constellation is shaped like a pentagon with Cappella, the brightest star, at one point.

Auriga is rich in open star clusters and nebulae (see IC 410 and IC 405, below) because the Milky Way (the view of one the galaxy's spiral arms) runs through the constellation. Among the open star clusters are three gems of particular beauty, all three noted by French astronomer Charles Messier in his famous catalog: M36, M37 & M38. All three clusters can be easily glimpsed with binoculars or a small telescope. The following images were taken with a 6" Newtonian reflector.

M36

Containing about three score stars, M36 is about 14 light years in diameter and is located about 4,100 light years away.

This image comprises three, five minute sub-exposures, for a total exposure time of 15 minutes.

M37

This cluster is considerably larger than M36, containing roughly 500 stars spread across a 25-light year diameter. M37 is located around 4,400 light years away and is thought to be about 300 million years old.

This image comprises five, five minute sub-exposures, for a total exposure time of 25 minutes.

M38

Located about 4,200 light years away, M38 has about the same diameter of M37 (around 25 light years), but appears to contain fewer member stars. NGC 1907, a smaller open cluster that appears near M38 is captured in the same field at the lower left of the image below.

This image comprises seven, five minute sub-exposures, for a total exposure time of 35 minutes.