¿ Astronomy Picture of the Day [1]Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2020 November 18 [2]See Explanation. Clicking on the picture will download the highest resolution version available. A Double Star Cluster in Perseus Image Credit & Copyright: [3]Greg Polanski Explanation: Most star clusters are singularly impressive. [4]Open clusters NGC 869 and NGC 884, however, could be considered doubly impressive. Also known as "h and chi Persei", this unusual [5]double cluster, shown above, is bright enough to be seen from a dark location without even [6]binoculars. Although their discovery surely predates [7]recorded history, the Greek astronomer [8]Hipparchus notably cataloged the [9]double cluster. The clusters are over 7,000 [10]light years distant toward the [11]constellation of [12]Perseus, but are separated by only hundreds of light years. In addition to being [13]physically close together, [14]the clusters' ages [15]based on their individual stars are similar - evidence that both [16]clusters were likely a product of the same [17]star-forming region. Tomorrow's picture: open space __________________________________________________________________ [18]< | [19]Archive | [20]Submissions | [21]Index | [22]Search | [23]Calendar | [24]RSS | [25]Education | [26]About APOD | [27]Discuss | [28]> __________________________________________________________________ Authors & editors: [29]Robert Nemiroff ([30]MTU) & [31]Jerry Bonnell ([32]UMCP) NASA Official: Phillip Newman [33]Specific rights apply. [34]NASA Web Privacy Policy and Important Notices A service of: [35]ASD at [36]NASA / [37]GSFC & [38]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/2011/DoubleCluster_Polanski_4560.jpg 3. mailto:%20gpolanski%20at%20teksavvy%20dot%20com 4. https://apod.nasa.gov/apod/open_clusters.html 5. https://en.wikipedia.org/wiki/Double_Cluster 6. https://en.wikipedia.org/wiki/Binoculars 7. https://en.wikipedia.org/wiki/Recorded_history 8. https://en.wikipedia.org/wiki/Hipparchus 9. https://apod.nasa.gov/apod/ap090103.html 10. http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html 11. https://en.wikipedia.org/wiki/Constellation 12. http://www.allthesky.com/constellations/perseus/ 13. https://dailykitten.com/wp-content/uploads/2007/12/1197579040cats-at-window-2.jpg 14. https://apod.nasa.gov/apod/ap090103.html 15. http://arxiv.org/abs/astro-ph/0104179v2 16. http://asterisk.apod.com/viewtopic.php?f=24&t=18009 17. https://apod.nasa.gov/apod/ap080928.html 18. https://apod.nasa.gov/apod/ap201117.html 19. https://apod.nasa.gov/apod/archivepix.html 20. https://apod.nasa.gov/apod/lib/apsubmit2015.html 21. https://apod.nasa.gov/apod/lib/aptree.html 22. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 23. https://apod.nasa.gov/apod/calendar/allyears.html 24. https://apod.nasa.gov/apod.rss 25. https://apod.nasa.gov/apod/lib/edlinks.html 26. https://apod.nasa.gov/apod/lib/about_apod.html 27. http://asterisk.apod.com/discuss_apod.php?date=201118 28. https://apod.nasa.gov/apod/ap201119.html 29. http://www.phy.mtu.edu/faculty/Nemiroff.html 30. http://www.phy.mtu.edu/ 31. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 32. http://www.astro.umd.edu/ 33. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 34. https://www.nasa.gov/about/highlights/HP_Privacy.html 35. https://astrophysics.gsfc.nasa.gov/ 36. https://www.nasa.gov/ 37. https://www.nasa.gov/centers/goddard/ 38. http://www.mtu.edu/