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 January 31 [2]See Explanation. Clicking on the picture will download the highest resolution version available. The Variable Nebula NGC 2261 Image Credit & [3]Copyright: [4]Tommy Lease (Denver Astronomical Society) Explanation: The interstellar cloud of dust and gas captured in this sharp telescopic snapshot is seen to change its appearance noticeably over periods as short as a few weeks. Discovered over 200 years ago and cataloged as NGC 2261, bright star R Monocerotis lies at the tip of the fan-shaped nebula. About one light-year across and 2500 light-years away, [5]NGC 2261 was studied early last century by astronomer Edwin Hubble and the mysterious cosmic cloud is now more famous as Hubble's Variable Nebula. So what makes Hubble's nebula vary? NGC 2261 is composed of a dusty [6]reflection nebula fanning out from the star [7]R Monocerotis. The leading [8]variability explanation holds that dense knots of obscuring dust pass close to [9]R Mon and cast [10]moving shadows across the dust clouds in the rest of [11]Hubble's Variable Nebula. Tomorrow's picture: light-weekend __________________________________________________________________ [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: Amber Straughn [27]Specific rights apply. [28]NASA Web Privacy Policy and Important Notices A service of: [29]ASD at [30]NASA / [31]GSFC, [32]NASA Science Activation & [33]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/2501/HubblesVariablecopy.jpg 3. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 4. https://www.instagram.com/colorado_astro/ 5. https://ui.adsabs.harvard.edu/abs/1916ApJ....44..190H/abstract 6. https://apod.nasa.gov/apod/reflection_nebulae.html 7. http://adsabs.harvard.edu/abs/1997ApJ...489..210C 8. http://adsabs.harvard.edu/abs/1978ApJ...226..455A 9. http://adsabs.harvard.edu/abs/1997ApJ...489..210C 10. https://bigamateurtelescope.com/project/hubbles-variable-nebula/ 11. https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-caldwell-catalog/caldwell-46/ 12. https://apod.nasa.gov/apod/ap250130.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=250131 22. https://apod.nasa.gov/apod/ap250201.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. https://science.nasa.gov/learners 33. http://www.mtu.edu/