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Sky Tonight—April 23, Two stars lead to constellation Hercules
Posted By Editor On April 23, 2011 @ 9:57 am In Earth & Sky | Comments Disabled
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 The constellation Hercules the Kneeling Giant can be seen ascending in the east-northeast on these spring evenings. Our chart today shows the sky for late night, when all of these objects are well up in the northeastern to eastern sky.
The stars Arcturus and Vega can help you identify Hercules, whose most noticeable pattern is a squarish figure in the center of the constellation. This sky pattern, or “asterism,” is known as the Keystone in Hercules.
The Keystone is a helpful pattern for more reasons than one. First, it is noticeable on the sky’s dome, so can lead your eye to Hercules. In addition, the Keystone in Hercules can help you find the most fascinating telescopic object within the boundaries of this constellation. This object is a globular star cluster . Known to stargazers as M13 or the Great Cluster in Hercules, it is barely visible the eye alone in the darkest of skies.
Binoculars show M13 as a nebulous patch. However, telescopes show stars both on the periphery of the cluster and toward its center. For a picture of M13 from the NOAO Image Gallery, look here .
This beautiful object is one of the galaxy’s oldest inhabitants. It is a tightly packed spherical collection of about one million stars.
By Deborah Byrd 
EarthSky: Space 
CHANDRA Photo Album 
Universe Today 
StarDate Online 
Sky and Telescope 
National Geographic 
Space Com 
Simostronomy Blog 
Amazing Space 
Scope City 
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URLs in this post:
 www.EarthSky.org: http://www.EarthSky.org
 Image: http://www.berthoudrecorder.com/wp-content/uploads/2011/04/phases-r-18.jpg
 Image: http://www.berthoudrecorder.com/wp-content/uploads/2011/04/apr23.jpg
 globular star cluster: http://seds.lpl.arizona.edu/messier/glob.html
 More on M13: Great cluster in Hercules: http://earthsky.org/clusters-nebulae-galaxies/m13-finest-globular-cluster-in-northern-skies
 here: http://www.noao.edu/image_gallery/html/im0551.html
 Deborah Byrd: http://earthsky.org/team/deborahbyrd
 Astronomy Picture of the Day from NASA/JPL: http://antwrp.gsfc.nasa.gov/apod/
 EarthSky: Space: http://earthsky.org/space
 CHANDRA Photo Album: http://chandra.harvard.edu/photo/
 U.S. Naval Observator Astronomical Information cente: http://www.usno.navy.mil/USNO/astronomical-applications/astronomical-information-center/astronomical-information-center
 Universe Today: http://www.universetoday.com/
 StarDate Online: http://stardate.org/
 Sky and Telescope: http://www.skyandtelescope.com/observing/ataglance/
 National Geographic: http://news.nationalgeographic.com/news/
 Space Com: http://www.space.com/nightsky/
 Simostronomy Blog: http://simostronomy.blogspot.com/
 Amazing Space: http://amazing-space.stsci.edu/tonights_sky/
 The York County Astronomical Society: http://www.ycas.org/tonights_sky.htm
 Scope City: http://www.scopecity.net/
 James S McDonnell Planetarium: http://www.slsc.org/WhatToDo/Planetarium/NightSkyUpdate.aspx
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