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 17 [2]A starfield surrounds a several large nebulas that appear mostly red but also white and blue. Dark dust and blue filaments also populate the frame. Please see the explanation for more detailed information. Nebulas and Clusters in Sagittarius Image Credit & Copyright: [3]J. De Winter, [4]C. Humbert, [5]C. Robert & [6]V. Sabet; Text: [7]Ogetay Kayali ([8]MTU) Explanation: Can you spot famous celestial objects in this image? 18th-century astronomer [9]Charles Messier cataloged only two of them: the bright [10]Lagoon Nebula (M8) at the bottom, and the colorful [11]Trifid Nebula (M20) at the upper right. The one on the left that resembles a [12]cat's paw is [13]NGC 6559, and it is much fainter than the other two. Even harder to spot are the thin blue filaments on the left, from [14]supernova remnant (SNR G007.5-01.7). Their glow comes from small amounts of [15]glowing oxygen atoms that are so faint that it took over [16]17 hours of exposure with just one blue color to bring up. Framing this scene of stellar birth and death are two star clusters: the [17]open cluster [18]M21 just above Trifid, and the [19]globular cluster [20]NGC 6544 at lower left. Tomorrow's picture: NGC 6914 __________________________________________________________________ [21]< | [22]Archive | [23]Submissions | [24]Index | [25]Search | [26]Calendar | [27]RSS | [28]Education | [29]About APOD | [30]Discuss | [31]> __________________________________________________________________ Authors & editors: [32]Robert Nemiroff ([33]MTU) & [34]Jerry Bonnell ([35]UMCP) NASA Official: Amber Straughn [36]Specific rights apply. [37]NASA Web Privacy, [38]Accessibility, [39]Notices; A service of: [40]ASD at [41]NASA / [42]GSFC, [43]NASA Science Activation & [44]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/2509/SagNebs_DeWinter_4550.jpg 3. https://www.instagram.com/dwj85 4. https://www.instagram.com/astro.berto54 5. https://www.instagram.com/charlesrbert 6. https://app.astrobin.com/u/victorf#gallery 7. https://www.ogetay.com/ 8. https://www.mtu.edu/physics/ 9. https://science.nasa.gov/people/explore-the-night-sky-hubbleatms-messier-catalog-bio/ 10. https://apod.nasa.gov/apod/ap250625.html 11. https://apod.nasa.gov/apod/ap240704.html 12. https://people.com/thmb/-ZwPce1JwYWjaTIEYYXePkDAFWo=/4000x0/filters:no_upscale():max_bytes(150000):strip_icc():focal(144x0:146x2)/000829300-1-166c18e3f54846d287baa774ae29b18e.jpg 13. https://apod.nasa.gov/apod/ap230710.html 14. https://science.gsfc.nasa.gov/662/research/snrs.html 15. https://en.wikipedia.org/wiki/Doubly_ionized_oxygen 16. https://app.astrobin.com/i/jliezm 17. https://en.wikipedia.org/wiki/Open_cluster 18. https://en.wikipedia.org/wiki/Messier_21 19. https://en.wikipedia.org/wiki/Globular_cluster 20. https://esahubble.org/images/potw2325a/ 21. https://apod.nasa.gov/apod/ap250916.html 22. https://apod.nasa.gov/apod/archivepix.html 23. https://apod.nasa.gov/apod/lib/apsubmit2015.html 24. https://apod.nasa.gov/apod/lib/aptree.html 25. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 26. https://apod.nasa.gov/apod/calendar/allyears.html 27. https://apod.com/feed.rss 28. https://apod.nasa.gov/apod/lib/edlinks.html 29. https://apod.nasa.gov/apod/lib/about_apod.html 30. https://asterisk.apod.com/discuss_apod.php?date=250917 31. https://apod.nasa.gov/apod/ap250918.html 32. http://www.phy.mtu.edu/faculty/Nemiroff.html 33. http://www.phy.mtu.edu/ 34. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 35. http://www.astro.umd.edu/ 36. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 37. https://www.nasa.gov/about/highlights/HP_Privacy.html 38. https://www.nasa.gov/general/accessibility/ 39. https://www.nasa.gov/privacy/ 40. https://astrophysics.gsfc.nasa.gov/ 41. https://www.nasa.gov/ 42. https://www.nasa.gov/centers/goddard/ 43. https://science.nasa.gov/learners 44. http://www.mtu.edu/