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. 2021 July 17 [2]See Explanation. Clicking on the picture will download the highest resolution version available. Alphonsus and Arzachel Image Credit & [3]Copyright: [4]Noel Donnard Explanation: [5]Point your telescope at tonight's first quarter Moon. [6]Along the terminator, the shadow line between night and day, you might find these two large craters staring back at you with [7]an owlish gaze. [8]Alphonsus (left) and [9]Arzachel are ancient impact craters on the north eastern shores of Mare Nubium, the lunar Sea of Clouds. The larger Alphonsus is over 100 kilometers in diameter. A low sun angle highlights the crater's sharp 1.5 kilometer high central peak in bright sunlight and dark shadow. Scouting for potential Apollo moon landing sites, the [10]Ranger 9 spacecraft returned closeup photographs of Alphonsus before it crashed in the crater just northeast (left) of its central mountain in 1965. [11]Alpetragius, between Alphonsus and Arzachel, is the small crater with the deeply shadowed floor and overly large central peak. Tomorrow's picture: 2.5 million light-years away __________________________________________________________________ [12]< | [13]Archive | [14]Submissions | [15]Index | [16]Search | [17]Calendar | [18]RSS | [19]Education | [20]About APOD | [21]Discuss | [22]> __________________________________________________________________ Authors & editors: [23]Robert Nemiroff ([24]MTU) & [25]Jerry Bonnell ([26]UMCP) NASA Official: Phillip Newman [27]Specific rights apply. [28]NASA Web Privacy Policy and Important Notices A service of: [29]ASD at [30]NASA / [31]GSFC & [32]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/2107/AlphonseArzachelOwl_Donnard.jpg 3. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 4. https://www.astrobin.com/users/Tino2329/ 5. https://www.astrobin.com/3sjnkh/B/ 6. https://apod.nasa.gov/apod/ap070209.html 7. https://en.wikipedia.org/wiki/Lunar_pareidolia 8. https://en.wikipedia.org/wiki/Alphonsus_(crater) 9. https://en.wikipedia.org/wiki/Arzachel_(crater) 10. https://solarsystem.nasa.gov/missions/ranger-9/in-depth/ 11. https://en.wikipedia.org/wiki/Alpetragius_(crater) 12. https://apod.nasa.gov/apod/ap210716.html 13. https://apod.nasa.gov/apod/archivepix.html 14. https://apod.nasa.gov/apod/lib/apsubmit2015.html 15. https://apod.nasa.gov/apod/lib/aptree.html 16. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 17. https://apod.nasa.gov/apod/calendar/allyears.html 18. https://apod.nasa.gov/apod.rss 19. https://apod.nasa.gov/apod/lib/edlinks.html 20. https://apod.nasa.gov/apod/lib/about_apod.html 21. http://asterisk.apod.com/discuss_apod.php?date=210717 22. https://apod.nasa.gov/apod/ap210718.html 23. http://www.phy.mtu.edu/faculty/Nemiroff.html 24. http://www.phy.mtu.edu/ 25. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 26. http://www.astro.umd.edu/ 27. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 28. https://www.nasa.gov/about/highlights/HP_Privacy.html 29. https://astrophysics.gsfc.nasa.gov/ 30. https://www.nasa.gov/ 31. https://www.nasa.gov/centers/goddard/ 32. http://www.mtu.edu/