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 August 4 [2]The Andromeda Galaxy is shown just right of center, while some unusual blue arcs appear to its left. Please see the explanation for more detailed information. Blue Arcs Toward Andromeda Image Credit & Copyright: [3]Ogle et [4]al. Explanation: What are these gigantic blue arcs near the Andromeda Galaxy (M31)? [5]Discovered in 2022 by amateur astronomers, the faint arcs -- dubbed [6]SDSO 1 -- span nearly the same angular size as M31 itself. At first, their origin was a mystery: are they actually [7]near the Andromeda Galaxy, or alternatively [8]near to our Sun? Now, over 550 hours of combined exposure and a collaboration between amateur and professional astronomers has revealed strong evidence for their true nature: SDSO 1 is not [9]intergalactic, but a new class of [10]planetary nebula within our galaxy. Dubbed a Ghost Planetary Nebula (GPN), SDSO 1 is the first recognized member of a new subclass of faded [11]planetary nebulas, along with seven others also [12]recently identified. Shown in blue are extremely faint [13]oxygen emission from the shock waves, while the [14]surrounding red is a hydrogen-emitting trail that indicates the GPN's age. Tomorrow's picture: complex stellar jumble __________________________________________________________________ [15]< | [16]Archive | [17]Submissions | [18]Index | [19]Search | [20]Calendar | [21]RSS | [22]Education | [23]About APOD | [24]Discuss | [25]> __________________________________________________________________ Authors & editors: [26]Robert Nemiroff ([27]MTU) & [28]Jerry Bonnell ([29]UMCP) NASA Official: Amber Straughn [30]Specific rights apply. [31]NASA Web Privacy, [32]Accessibility, [33]Notices; A service of: [34]ASD at [35]NASA / [36]GSFC, [37]NASA Science Activation & [38]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/2508/M31Oxy_Collab_5415.jpg 3. https://arxiv.org/abs/2507.15834 4. https://www.astrobin.com/ns2x09/ 5. https://iopscience.iop.org/article/10.3847/2515-5172/acaf7e 6. https://www.astrobin.com/1d8ivk/ 7. https://apod.nasa.gov/apod/ap230117.html 8. https://www.reddit.com/r/CatsBeingCats/comments/17psiw8/cats_basking_in_a_sun_bath/#lightbox 9. https://science.nasa.gov/asset/hubble/intergalactic-absorbtion-clouds/ 10. https://apod.nasa.gov/apod/ap250713.html 11. https://science.nasa.gov/category/universe/nebulae/planetary-nebulae/ 12. https://arxiv.org/abs/2507.15834 13. https://www.astronomy.com/science/oxygen-the-color-of-life/ 14. https://apod.nasa.gov/apod/ap221024.html 15. https://apod.nasa.gov/apod/ap250803.html 16. https://apod.nasa.gov/apod/archivepix.html 17. https://apod.nasa.gov/apod/lib/apsubmit2015.html 18. https://apod.nasa.gov/apod/lib/aptree.html 19. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 20. https://apod.nasa.gov/apod/calendar/allyears.html 21. https://apod.com/feed.rss 22. https://apod.nasa.gov/apod/lib/edlinks.html 23. https://apod.nasa.gov/apod/lib/about_apod.html 24. https://asterisk.apod.com/discuss_apod.php?date=250804 25. https://apod.nasa.gov/apod/ap250805.html 26. http://www.phy.mtu.edu/faculty/Nemiroff.html 27. http://www.phy.mtu.edu/ 28. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 29. http://www.astro.umd.edu/ 30. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 31. https://www.nasa.gov/about/highlights/HP_Privacy.html 32. https://www.nasa.gov/general/accessibility/ 33. https://www.nasa.gov/privacy/ 34. https://astrophysics.gsfc.nasa.gov/ 35. https://www.nasa.gov/ 36. https://www.nasa.gov/centers/goddard/ 37. https://science.nasa.gov/learners 38. http://www.mtu.edu/