Weekly Cosmos Report - Baja Night Sky #82

Date: 20/04/2015

Monday, April 20, 2015:

M13 star cluster

1) Step outside around 8:30pm this evening and look for the two-day-old crescent moon two fists above the horizon. A fist to its right is the Pleiades cluster, and above them shines Venus. The three form a nice triangle. Aldebaran, a red giant in the late stages of life, is just to the left of Venus. Without binoculars, it is much harder to spot Mars and Mercury almost ready to set below the Pleiades.

2) The Big Dipper is standing on its handle high in the NE. Follow the arc of its handle to Arcturus high in the east. This is the 4th brightest star in our night sky. It happens to be passing through the Milky Way at 120+miles/sec. In just a few tens of millions of years it will exit the other side and continue on its way across the universe. Even at this speed, it is so far away that in the last 2000 years it has only changed position in the night sky by about a Moon's width.

3) The annual Lyrid meteor shower has already begun. It should reach a peak between late evening Wednesday, April 22, and a couple hours before dawn on Thursday. The peak rate is usually around 10 to 15 per hour. There is a good chance this year's rate will be higher. Most of the shooting stars you will see are about 50 miles above us and no bigger than a grain of sand or at most a pea.

4) This section is for hard-core stargazers. If you are still awake at 11pm look to the east (or wait until 9pm mid May if you are still in Baja). Binoculars will be helpful. Find Vega, the 5th brightest star, rising low in the NE. Draw a line in your imagination from Arcturus down to Vega, then retrace 1/3 of the distance back towards Arcturus. If your sky is dark and your night vision finally awake, look for the four stars making up the Keystone asterism in the constellation Hercules. They almost form a square. Find the top two (most western) stars of the Keystone. Go 1/3 of the distance from the top left star to the top right star. Use binoculars to scan this region. Look for a fuzzy blob, bright at the center and fading out to the edges. Use averted vision to see its details. This is the Famous M13 Great Globular Cluster in Hercules. It contains close to a million stars, old ones -- more than 12 billion years compared to our young sun of 4.5 billion. Those near the center are packed 500 times as close together as the stars near our sun. Imagine a night sky with 1000 stars brighter than Sirius! Imagine the length of the BNS! This cluster is orbiting around the center of the Milky way at a distance from us of about 25,000 light years. Through a medium-size telescope it is spectacular.

Have a great summer! Tom at

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