Let's look at what we are seeing here.
1) This is the yellow Antares nebula. Antares
itself, a red supergiant, is the bright star to the lower right inside this nebula. Antares is rounder, smaller and a bit more well-behaved than the other famous red supergiant star in the sky, Betelgeuse. The yellow color of the nebula surrounding Antares is due to several factors, such as dust reddening and some scattered red Hα light, but mostly the nebula is a reflection nebula where yellow light from Antares has been scattered.
2) This is a globular cluster, NGC 6144
3) This is a small group of blue stars that belong to the "Antares group". The brightest of these is 22 Scorpii, a main sequence star of spectral class B3V. The star is surrounded by a blue reflection nebula, IC 4605
, of its own making.
4) This is a relatively dust-reddened star of spectral class A, surrounded by nebula IC 4603
.Most fascinating, however, is the fact that right next to this star, deeply embedded in dust, many new baby stars are being hatched
5) This is the rather famous blue Rho Ophiuchi reflection nebula. It is centered on a small group of B- and A-type main seuence stars, the brightest of which is Rho Ophiuchi itself, a star of spectral class B2V. It is the blue light of these stars that is scattered in the dusty nebula to make it look blue.
6) This is Sigma Scorpii, a binary star where one of the components belongs to spectral class O9.5V and is therefore hot enough to ionize a red emission nebula. Sigma Scorpii is surrounded by both a blue reflection nebula and a red emission nebula, as can be seen in this photo
by Rolf Scheffer and the Astrofarm Kiripotib Namibia.
7) This is globular cluster M4
8) This is the large but faint red reflection nebula surrounding star Tau Scorpii, a star of spectral class B0V. It is hot enough to ionize a faint red emission nebula. The star itself can't be seen in today's APOD.
Finally, let's compare today's APOD with the much more widefield picture of the same area in a photo (and an APOD
) by Mario Cogo.
You can see the large pink nebula at lower left, surrounding Tau Scorpii. That pink nebula was number 8 in my annotated version of today's APOD.
Above and to the right of the pink Tau Scorpii nebula is the yellow Antares nebula. To the right of the yellow Antares nebula is globular cluster M4. Anbove and to the right of M4 is the rather small-looking pink and blue nebula surrounding (fairly bright-looking) Sigma Scorpii. To the left of Sigma Scorpii is 22 Scorpii and its small blue nebula. The very dark dusty nebula above and to the right of 22 Scorpii is where baby stars are being born. Above it is the blue Rho Ophiuchi nebula.
Above and to the right of the Roho Ophiuchi nebula is the Blue Horse nebula
. The Blue Horse appears to be staring at the star Beta Scorpii.
Below and to the right of Beta Scorpii is Delta Scorpii, surrounded by a large but faint red emission nebula.
Below Delta Scorpii is Pi Scorpii, surrounded by a red emission nebula and a very funny-looking, angular blue reflection nebula.
Oh, and - you can never have enough pictures of this utterly fascinating region of the sky. Each picture shows you a new way of looking at this amazing nebular starscape. How about this beauty by Warren Keller, Jim Misti and Steve Mazlin?
Well, that's it for me today, I think!
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