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 April 4 [2]See Explanation. Clicking on the picture will download the highest resolution version available. Hickson 44 in Leo Image Credit & [3]Copyright: [4]Jiang Wu Explanation: Scanning the skies for galaxies, Canadian astronomer Paul Hickson and colleagues identified some 100 compact [5]groups of galaxies, now appropriately called [6]Hickson Compact Groups. The four prominent galaxies seen in this intriguing [7]telescopic skyscape are one such group, Hickson 44. The galaxy group is about 100 million light-years distant, far beyond the spiky foreground Milky Way stars, toward the constellation Leo. The two spiral galaxies in the center of the image are edge-on NGC 3190 with its distinctive, warped dust lanes, and S-shaped NGC 3187. Along with the bright elliptical, NGC 3193 (above and left) they are also known as Arp 316. The spiral toward the lower right corner is NGC 3185, the 4th member of the Hickson group. Like other galaxies in [8]Hickson groups, these show signs of distortion and [9]enhanced star formation, evidence of a gravitational tug of war that will eventually result in galaxy mergers on a cosmic timescale. The merger process is now understood to be a normal part of the evolution of galaxies, including [10]our own Milky Way. For scale, [11]NGC 3190 is about 75,000 light-years across at the estimated distance of Hickson 44. 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/2504/ARP316.jpg 3. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 4. https://app.astrobin.com/u/175892800@qq.com 5. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1989ApJS...70..687H&db_key=AST&high=39d9fcfee518892 6. http://www.deep-sky.co.uk/observing/galaxies/hickson.htm 7. https://app.astrobin.com/u/175892800@qq.com?i=47pbiv#gallery 8. https://asterisk.apod.com/viewtopic.php?f=29&t=25085 9. https://apod.nasa.gov/apod/ap061024.html 10. https://apod.nasa.gov/apod/ap220606.html 11. https://apod.nasa.gov/apod/ap100503.html 12. https://apod.nasa.gov/apod/ap250403.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=250404 22. https://apod.nasa.gov/apod/ap250405.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/