Gems of the Winter Sky
by Ralf Rohner
Title
Gems of the Winter Sky
Artist
Ralf Rohner
Medium
Photograph
Description
Here is the second part of my tour of the Winter sky of my image 'Contact'. Let's take a closer look at some deep sky objects from far to close:
At the very top of the image, you can see two blue circles, containing cutouts of the farthest objects in the image. M74 and M33, the Triangulum Galaxy. Both are spiral galaxies, like our Milky Way. M74 appears tiny because it is 32 million light-years away from Earth, while M33 is ten times closer at 2.73 ly. The Triangulum Galaxy is the third largest galaxy of our local group, behind the Milky Way and the Andromeda Galaxy. I was surprised that I was able to capture its spiral structure with my 24mm lens.
The orange circles mark open clusters. An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, whereof the Pleiades and the Hyades, which take the center stage in this image, are among the best known. I also marked the clusters that were contained in the famous catalogue from French astronomer Charles Messier, dating back to 1781. There are many more open clusters in the image, but I decided not to mark them to avoid cluttering the image.
Open clusters sometimes still contain interstellar dust, which reflects the light from the young stars. The Pleiades are displaying such a reflection nebula. You can see it as a rather strong blue glow around its stars.
Young open clusters may be contained within the molecular cloud from which they formed, illuminating it to create an H II region, glowing in the red light of ionized Hydrogen. Over time, radiation pressure from the cluster will disperse the molecular cloud.
The famous Orion Nebula M42 is such a H ll region, where young stars are being formed right now. It can be seen above the radio dish.
Other examples are the Seagull Nebula, the Rosette Nebula, the California Nebula and the Flame Nebula.
The red Barnard's Loop is also glowing in the light of ionized Hydrogen, but it is a special case. It is ionized by the stars in the Orion Nebula, but the Hydrogen originated from a supernova explosion about 2 million years ago.
The same supernova explosion was also responsible for several runaway stars, including AE Aurigae, which is lighting the Flaming Star Nebula.
The Angelfish Nebula is another example of supernova remnants that are ionized by a bright star. In thus case it is Meissa (Lambda Orionis).
The extremely faint Witchhead Nebula, visible above the radio dish, probably is a supernova remnant too. Contrary to those explained above, it however is a reflection nebula. The dust remaining dust of this supernova is not glowing because it is ionized, but it reflects the light of the nearby supergiant star Rigel.
If a dying star, is too small to end its life in a spectacular supernova explosion, it will shed its atmosphere and become a white dwarf, the glowing embers of the now inactive stellar core that will eventually cool down and stop glowing. The expanding ionized shell of the stars shed atmosphere will glow a few 10'000 yeras as a planetary nebula. Such a planetary nebula is visible on the lower right of the image. As it is pretty small, I made a full resolution cutout to better show it. It is a good example of the fate that is awaiting our own Sun.
With this we have arrived in our solar system. Jupiter, Mars and Saturn have put up quite a show this summer, but you probably have never seen the planet in this image: Uranus Although theoretically visible by naked eye from a dark sky site, it is just another dim point among the stars without the aid of a telescope. I circled it red to help you locate it.
Another solar system object that has put up a show this year was Comet Neowise. It may help to understand how special Neowise was if you see C/2020 M3 (ATLAS), which is still considered a rather bright Comet. You find it as a green blob between Bellatrix and Orion's Belt. I made another full resolution cutout to show it a bit better.
The radiation of our Sun not only makes Comets glow, it is also responsible for a dim glow in the night sky, called the Zodiac Band. The diffuse brightening of the sky is caused by sunlight reflected on interplanetary dust, left behind by Comets and colliding asteroids. The brightest spot, called Gegenschein, is located directly opposite to the sun, where the dust particles are fully illuminated (like a full moon). The bigness of the Zodiac Band gradually falls off farther away from the Gegenschein, as the dust becomes only partially illuminated (like a gibbous Moon).
The last object I would like to point out is also associated with a Comet, but it is already within Earth's atmosphere. It is a Northern Taurid Meteor. As their name implies, the Northern Taurids appear to originate from a radiant in the northern part of the constellation Taurus. They are caused by dust from Comet 2P/Encke burning up in our atmosphere.
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December 1st, 2020
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