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. 2019 October 6 [2]See Explanation. Clicking on the picture will download the highest resolution version available. The Horsehead Nebula Image Credit & Copyright: [3]José Jiménez Priego Explanation: The [4]Horsehead Nebula is one of the most famous nebulae on the sky. It is visible as the dark indentation to the red [5]emission nebula in the center of the above photograph. The [6]horse-head feature is dark because it is really an opaque [7]dust cloud that lies in front of the bright red [8]emission nebula. Like clouds in [9]Earth's atmosphere, this cosmic cloud has assumed a [10]recognizable shape by chance. After many thousands of years, the internal motions of the cloud will surely alter its appearance. The emission [11]nebula's red color is caused by [12]electrons recombining with [13]protons to form [14]hydrogen atoms. On the image left is the [15]Flame Nebula, an orange-tinged nebula that also contains filaments of dark dust. Just to the lower left of the Horsehead nebula [16]featured picture is a blueish [17]reflection nebulae that preferentially [18]reflects the blue light from [19]nearby stars. Tomorrow's picture: jupiter spotted __________________________________________________________________ [20]< | [21]Archive | [22]Submissions | [23]Index | [24]Search | [25]Calendar | [26]RSS | [27]Education | [28]About APOD | [29]Discuss | [30]> __________________________________________________________________ Authors & editors: [31]Robert Nemiroff ([32]MTU) & [33]Jerry Bonnell ([34]UMCP) NASA Official: Phillip Newman [35]Specific rights apply. [36]NASA Web Privacy Policy and Important Notices A service of: [37]ASD at [38]NASA / [39]GSFC & [40]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/1910/HorseFlame_Priego_3252.jpg 3. https://www.facebook.com/jose.jimenezjj 4. https://en.wikipedia.org/wiki/Horsehead_nebula 5. https://apod.nasa.gov/apod/emission_nebulae.html 6. https://apod.nasa.gov/apod/ap140728.html 7. https://apod.nasa.gov/apod/ap030706.html 8. https://en.wikipedia.org/wiki/Emission_nebula 9. http://www.nasa.gov/mission_pages/sunearth/science/atmosphere-layers2.html 10. http://www.brucevanpatter.com/cloudshapes.html 11. https://apod.nasa.gov/apod/ap061015.html 12. http://www.pbs.org/transistor/science/events/electron.html 13. http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html 14. http://periodic.lanl.gov/1.shtml 15. https://apod.nasa.gov/apod/ap141209.html 16. https://www.flickr.com/photos/astromet/21844852965/in/album-72157634385115181/ 17. https://apod.nasa.gov/apod/reflection_nebulae.html 18. https://spaceplace.nasa.gov/blue-sky/en/ 19. https://apod.nasa.gov/apod/ap010318.html 20. https://apod.nasa.gov/apod/ap191005.html 21. https://apod.nasa.gov/apod/archivepix.html 22. https://apod.nasa.gov/apod/lib/apsubmit2015.html 23. https://apod.nasa.gov/apod/lib/aptree.html 24. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 25. https://apod.nasa.gov/apod/calendar/allyears.html 26. https://apod.nasa.gov/apod.rss 27. https://apod.nasa.gov/apod/lib/edlinks.html 28. https://apod.nasa.gov/apod/lib/about_apod.html 29. http://asterisk.apod.com/discuss_apod.php?date=191006 30. https://apod.nasa.gov/apod/ap191007.html 31. http://www.phy.mtu.edu/faculty/Nemiroff.html 32. http://www.phy.mtu.edu/ 33. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 34. http://www.astro.umd.edu/ 35. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 36. https://www.nasa.gov/about/highlights/HP_Privacy.html 37. https://astrophysics.gsfc.nasa.gov/ 38. https://www.nasa.gov/ 39. https://www.nasa.gov/centers/goddard/ 40. http://www.mtu.edu/