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. 2025 September 2 [2]A starfield is shown with bright and dark nebulae of different shapes and colors. Please see the explanation for more detailed information. The Horsehead and Flame Nebulas Image Credit & Copyright: [3]Daniel Stern Explanation: The [4]Horsehead Nebula is one of the most famous nebulae on the sky. It is visible as the dark indentation to the orange [5]emission nebula at the far right of the [6]featured picture. The [7]horse-head feature is dark because it is really an opaque [8]dust cloud that lies in front of the bright [9]emission nebula. Like clouds in [10]Earth's atmosphere, this cosmic cloud has assumed a [11]recognizable shape by chance. After [12]many thousands of years, the internal motions of the cloud will surely alter its appearance. The emission [13]nebula's orange color is caused by [14]electrons recombining with [15]protons to form [16]hydrogen atoms. Toward the lower left of the image is the [17]Flame Nebula, an orange-tinged nebula that also contains intricate filaments of dark dust. Tomorrow's picture: star jet __________________________________________________________________ [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: Amber Straughn [33]Specific rights apply. [34]NASA Web Privacy, [35]Accessibility, [36]Notices; A service of: [37]ASD at [38]NASA / [39]GSFC, [40]NASA Science Activation & [41]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/2509/OrionHorseHead_Stern_5842.jpg 3. https://www.instagram.com/messierchaser/ 4. https://en.wikipedia.org/wiki/Horsehead_nebula 5. https://en.wikipedia.org/wiki/Emission_nebula 6. https://www.instagram.com/p/DFRDLZ0uUoF/ 7. https://apod.nasa.gov/apod/ap140728.html 8. https://apod.nasa.gov/apod/ap030706.html 9. https://astronomy.swin.edu.au/cosmos/E/emission+nebula 10. https://www.nasa.gov/image-article/earths-atmospheric-layers-3/ 11. https://apod.nasa.gov/apod/ap240114.html 12. https://cdn.shopify.com/s/files/1/0272/4770/6214/articles/do-cats-get-bored-800x533.jpg 13. https://apod.nasa.gov/apod/ap061015.html 14. https://history.aip.org/exhibits/electron/ 15. https://home.cern/news/news/physics/proton-century 16. https://periodic.lanl.gov/1.shtml 17. https://apod.nasa.gov/apod/ap210412.html 18. https://apod.nasa.gov/apod/ap250901.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.com/feed.rss 25. https://apod.nasa.gov/apod/lib/edlinks.html 26. https://apod.nasa.gov/apod/lib/about_apod.html 27. https://asterisk.apod.com/discuss_apod.php?date=250902 28. https://apod.nasa.gov/apod/ap250903.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://www.nasa.gov/general/accessibility/ 36. https://www.nasa.gov/privacy/ 37. https://astrophysics.gsfc.nasa.gov/ 38. https://www.nasa.gov/ 39. https://www.nasa.gov/centers/goddard/ 40. https://science.nasa.gov/learners 41. http://www.mtu.edu/