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Dudley Observatory
Supporting research and education in astronomy, astrophysics, and the history of astronomy |
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Skywatch September 2004
SKY WATCH Thursday September 2, 2004 by Barlow Bob
Observe the Full Moon on August 29th and the Last Quarter Moon on September 6th.
Observe the most beautiful double sky of the summer sky called Albireo, in the constellation Cygnus the Swan. Find the Summer Triangle, stretching from high overhead off to the south. The eastern most of the stars is Deneb, which sits at the top of the Northern Cross (or, if you prefer, at the tail of Cygnus the Swan). The cross runs to the south and west, going right between the other two stars of the triangle, Vega and Altair. Albireo is the star at the foot of the cross.
In the finder scope: Albireo is quite easy to find, being the brightest star in the immediate neighborhood. In the telescope: the double star is easy to split, even at moderate powers, and the color contrast is striking.
Albireo is the standard against which all other doubles are judged. The attractions of this double star are many. First, it is quite easy to find. Second, it is well separated, and therefore easy to split; yet the two components are close enough together and close enough in brightness that they make a nice pair. But the biggest attraction of this pair is the color contrast. If you have ever doubted that stars have colors, this pair should remove any doubt.
The colors stand out best at low to medium magnification, in a small telescope. A little bit of sky brightness (twilight, or a Full Moon) can actually help your eye appreciate the colors. Some observers like to look at these stars very slightly out of focus to emphasize the colors.
Albireo is made up of a giant orange Spectral type K) star, orbited by a hot blue (spectral type B) star. Star B lies at least 4,500 AU away from A. AU stands for one Astronomical Unit or the distance from the Sun to the Earth. These two stars are 4,500 times farther away from each other than we are from the Sun. It must take about 100,000 years to complete an orbit about it. The two stars lie 400 light years away from the Earth. You are looking at the stars as the appeared in the year 1604 on Earth.
SKY WATCH Thursday September 9, 2004 by Barlow Bob
Observe the Full Moon on August 29th and the Last Quarter Moon on September 6th.
Observe the most beautiful double sky of the summer sky called Albireo, in the constellation Cygnus the Swan. Find the Summer Triangle, stretching from high overhead off to the south. The eastern most of the stars is Deneb, which sits at the top of the Northern Cross (or, if you prefer, at the tail of Cygnus the Swan). The cross runs to the south and west, going right between the other two stars of the triangle, Vega and Altair. Albireo is the star at the foot of the cross.
In the finder scope: Albireo is quite easy to find, being the brightest star in the immediate neighborhood. In the telescope: the double star is easy to split, even at moderate powers, and the color contrast is striking.
Albireo is the standard against which all other doubles are judged. The attractions of this double star are many. First, it is quite easy to find. Second, it is well separated, and therefore easy to split; yet the two components are close enough together and close enough in brightness that they make a nice pair. But the biggest attraction of this pair is the color contrast. If you have ever doubted that stars have colors, this pair should remove any doubt.
The colors stand out best at low to medium magnification, in a small telescope. A little bit of sky brightness (twilight, or a Full Moon) can actually help your eye appreciate the colors. Some observers like to look at these stars very slightly out of focus to emphasize the colors.
Albireo is made up of a giant orange Spectral type K) star, orbited by a hot blue (spectral type B) star. Star B lies at least 4,500 AU away from A. AU stands for one Astronomical Unit or the distance from the Sun to the Earth. These two stars are 4,500 times farther away from each other than we are from the Sun. It must take about 100,000 years to complete an orbit about it. The two stars lie 400 light years away from the Earth. You are looking at the stars as the appeared in the year 1604 on Earth.
THURSDAY SEPTEMBER 16, 2004 by Barlow Bob
Observe the Full Moon on September 28th and Last Quarter Moon on October 6th.
The Constellation Cassiopeia contains many open clusters of stars. The most beautiful and interesting cluster is named NGC 457. This is the 457th entry in the New General Catalog of celestial objects. Most open clusters are just groups of stars with undefined shapes. Some are large and others just small loose clusters of stars.
Find Cassiopeia, a W shape of five stars overhead, towards the northeast. Number the stars of the W 1 to 5, from left to right. To find NGC 457, step from star 1 named Epsilon Cassiopeia to star 2 named Ruchbah and continue one third that distance farther. That is where NGC 436 is located. You will see a star in the finder scope called Phi Cassiopeia, a bit south and eat of this point; NGC 457 stretches out to the northeast from this star.
NGC 457 is located about 9,000 light years away from us. It consists of about 200 stars, in a region about 30 light years in diameter. It is not clear whether or not Phi Cassiopeia is actually a member of this cluster. Because it is so much brighter than the other stars in the cluster, one would first assume that it is actually much closer to us than the cluster stars, and just happens to lie along the same line of sight. However, it appears to be moving in space at the same rate as the other stars. It is a yellow super giant, consistent with what you would expect for a star in the cluster that had evolved through its “red giant” phase. If it really is part of the cluster, and as far away from us as the other cluster stars, then it would have to be one of the brightest stars in the galaxy.
NGC 457 is called the Owl Cluster, since it appears as a little upside down owl. Some call this the ET cluster, after ET the extraterrestrial in the movie. Others see this open cluster as a dragonfly or butterfly. Please do not observe Cassiopeia without stopping to study NGC 457. This is the best object to show children of all ages in telescopes of any size. It would appear only as a small fuzzy patch in binoculars.
THURSDAY SEPTEMBER 23, 2004 by Barlow Bob Observe the Full Moon on September 28th and Last Quarter Moon on October 6th.
The Constellation Cassiopeia contains many open clusters of stars. The most beautiful and interesting cluster is named NGC 457. This is the 457th entry in the New General Catalog of celestial objects. Most open clusters are just groups of stars with undefined shapes. Some are large and others just small loose clusters of stars.
Find Cassiopeia, a W shape of five stars overhead, towards the northeast. Number the stars of the W 1 to 5, from left to right. To find NGC 457, step from star 1 named Epsilon Cassiopeia to star 2 named Ruchbah and continue one third that distance farther. That is where NGC 436 is located. You will see a star in the finder scope called Phi Cassiopeia, a bit south and eat of this point; NGC 457 stretches out to the northeast from this star.
NGC 457 is located about 9,000 light years away from us. It consists of about 200 stars, in a region about 30 light years in diameter. It is not clear whether or not Phi Cassiopeia is actually a member of this cluster. Because it is so much brighter than the other stars in the cluster, one would first assume that it is actually much closer to us than the cluster stars, and just happens to lie along the same line of sight. However, it appears to be moving in space at the same rate as the other stars. It is a yellow super giant, consistent with what you would expect for a star in the cluster that had evolved through its “red giant” phase. If it really is part of the cluster, and as far away from us as the other cluster stars, then it would have to be one of the brightest stars in the galaxy.
NGC 457 is called the Owl Cluster, since it appears as a little upside down owl. Some call this the ET cluster, after ET the extraterrestrial in the movie. Others see this open cluster as a dragonfly or butterfly. Please do not observe Cassiopeia without stopping to study NGC 457. This is the best object to show children of all ages in telescopes of any size. It would appear only as a small fuzzy patch in binoculars. |
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