A Comet’s Day

This sequence of 23 images of Comet 67P/Churyumov–Gerasimenko was taken with Rosetta‘s OSIRIS narrow-angle camera on 4 July, 2015, about a month before the comet’s closest approach to the Sun. They were taken at 30 minute intervals and span a full “day” at the comet which spins around its axis in roughly 12.4 hours. The images reveal daily color changes on the surface. The bluer areas are richer in water ice than their redder surroundings. A daily cycle of water ice occurs at the comet. Water quickly turns into water vapor when exposed to sunlight during the local daytime, and it condenses back into thin layers of frost and ice as the temperature drops after sunset. Then it sublimate again on the following day. The Sun is toward the top of the frame.

Video Credit: ESA

NGC 1483

ngc-1483-smallNGC 1483 us a barred spiral galaxy a bit over 60 million light-years away.  Barred spiral galaxies are so named because of the prominent bar-shaped structures found in their center. Roughly two-thirds of all spiral galaxies, including the Milky Way, are barred. It’s been suggested that bars may be a common stage in the formation of spiral galaxies and may indicate that a galaxy has reached full maturity.

Image Credit: ESA / NASA

NGC 299

The Toucan and the clusterNGC 299 is an open star cluster located within the Small Magellanic Cloud about 200,000 light-years away. Open clusters are groups of stars  of which formed from the same massive cloud of gas and dust and are loosely held together by gravity. All the stars have roughly the same age and composition, but they vary in their mass because they formed at different positions within the cloud.

Image Credit: ESA / NASA