Skywatch Line for Monday and Tuesday, April 9th and 10th, 2018

This is the Skywatch Line for Monday and Tuesday, April 9th and 10th.

The Sun sets at 7:30 PM; night falls at 9:11. Dawn begins at 4:42 AM and ends with the Sun rising at 6:22.

The twilight sky has only one bright planet – Venus. Located in Aries, the planet shines with minus 4th magnitude, appears a medium size of 11 arc-seconds and is about 93 percent illuminated. Moderately low in the western sky, it sets at 9:23 PM.

Jupiter rises in Libra and is the brightest object in the constellation. Jupiter rises at 10:03 PM, and by midnight, is 17 degrees high in the eastern sky. Telescopic observers can see the Great Red Spot (a giant storm) at 10:34 PM Monday, and at 4:21 AM on Wednesday. They can also, at 11:17 PM on Tuesday, witness the moon Europa’s shadow leave the Jovian surface, followed by the moon itself at 12:29 AM. Jupiter is best observed at 3:00 AM.

Dawn sees Sagittarius as the site of the main attractions. Saturn rises 1:46 AM, shining at 0.5 magnitude, 17 arc-seconds in size and 21 degrees high in the western sky. The Ringed Planet lies about 47 degrees east of Jupiter. Binocular observers can see the rings tilted nearly to maximum – 25.5 degrees. They can also see Saturn 1 degree above globular star cluster M-22, 4 degrees from globular star cluster M-28 and 3 degrees below open star cluster M-25. Telescopic observers can, at 4:00 AM Tuesday, see 5 Saturnian moons clustered about the planet.

Mars also inhabits Sagittarius, rising at 2:09 AM, shining at zero magnitude and 9 arc-seconds in size. It appears about 88 percent illuminated. Mars is gradually growing brighter, larger, and beginning to be worthy of studying surface features. Sagittarius has one more visitor, 4Vesta. This asteroid is 512 km (312 mi) in diameter and is appropriately small in our telescopes. It rises at 12:55 AM and shines with 7th magnitude, within most amateur telescopes. Observers should consult websites and magazines for detailed finder charts.

Finally, the Moon rises in Capricornus at 3:47 AM Tuesday, and 4:22 AM on Wednesday. It shines at minus 8th magnitude and is 31 percent phase on Tuesday, and 22 percent on Wednesday.

Earlier, we mentioned that Saturn and Mars lie quite close to several star clusters. Throughout the night, star clusters abound. In early evening, we find the Pleiades above the shoulders of Taurus. The Bull’s face is made of another star cluster, the Hyades. The nearby constellation Auriga harbors three clusters. Finally, Cancer contains the Beehive and M 67.

All these are called “Open Clusters.” They appear to contain, at most, a few hundred stars, which are widely spaced and irregularly shaped. Open clusters are relatively young, less than a billion years old. They reside in the disk of a galaxy and are relatively small, about 50 light-years across.

There is another class of star clusters, called “Globular Clusters.” Globular clusters are usually found around galaxy halos and central bulges.
Globulars may contain up to a million stars and are quite large, in a sphere about 100 light-years across. These stars are quite old.

If tonight’s weather is clear, binoculars can show many Open Clusters. Just dress warmly and observe the Hyades, Pleiades and the nearby pentagon shaped constellation Auriga.

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