APOD: Messier 20 and 21 (2019 Dec 30)

[APOD Robot]

Messier 20 and 21

Explanation: The beautiful Trifid Nebula, also known as Messier 20, is easy to find with a small telescope in the nebula rich constellation Sagittarius. About 5,000 light-years away, the colorful study in cosmic contrasts shares this well-composed, nearly 1 degree wide field with open star cluster Messier 21 (top left). Trisected by dust lanes the Trifid itself is about 40 light-years across and a mere 300,000 years old. That makes it one of the youngest star forming regions in our sky, with newborn and embryonic stars embedded in its natal dust and gas clouds. Estimates of the distance to open star cluster M21 are similar to M20's, but though they share this gorgeous telescopic skyscape there is no apparent connection between the two. In fact, M21's stars are much older, about 8 million years old.

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[Ann]

Tjohoo! (That's Swedish for Woo-hoo!) A beautiful, lovely, RGB (and probably Hα) saturated color of a region of sky that any lover of blue nebulas and blue stars (offset with a bit of blooming pink) has to love!

I just love the palette of colors here. Note how the emission nebula is pale and mixed with blue near the ionizing star HD 164492 - there's probably a reflection component here - and how the color of the emission nebula then becomes neutral as we move outwards, probably because we are seeing a mixture of Hα and OIII, and how the red color grows ever redder the farther away from the ionizing star we get. Note how the red component is "contained" inside dust structures in places.

Click to view full size image

Yellow star HD 164514 and the blue part of the Trifid Nebula.
Photo: R. Jay GaBany.

Note how the blue reflection nebula appears to be enhanced by the bright yellow star HD 164514. This star appears to be a main contributor to the reflection nebulosity. Note, however, that the blue nebula is not at its very brightest near the yellow star, which is the opposite of what the reflection nebulosity is like in the Pleiades. So when all is said and done, I'm not absolutely sure how much the yellow star contributes. David Malin once took a picture of the Lagoon Nebula which showed a blue component outside the pink one, so maybe most of the blue nebulosity of the Trifid is caused by HD 164492 and the other hot blue stars near it. It seems certain that rest of the the pale blue nebulosity encircling the pink part of the Trifid Nebula is the works of HD 164492.

As for the blue nebulosity of the Trifid Nebula, I guess it is possible that the hot blue stars north of the Trifid Nebula (particularly HD 164402) may contribute. This star doesn't wear a "veil" of blue nebulosity around it, but it may easily have blown its natal clouds away. But its light just might reach the northern parts of the Trifid, just like the blue light of Rigel illuminates the Witchhead Nebula.

I also love the little tufts of red emission nebulosity scattered near the Trifid! But note that there is no nebulosity near M21 at all. This beautiful cluster of bright blue stars is old enough to have blown all the gas and dust away from it!

Click to view full size image

The Trifid Nebula and M21. Photo: Daniel Carache.

I had to include a picture of the Trifid Nebula with M21. But I couldn't just copy today's APOD, because it is too big to post here! Sorry! But Daniel Carache's Tririd is nice too, though its colors and other details are a little bit different than Stanislav Volskiy's and the Chilescope Team. But a well-made RGB image of the Trifid is always a joy to behold, so enjoy!!!

Ann

[Boomer12k]

Awesome and beautiful image... both 20 and 21 together... a great field of view...
With my 10" Meade I get a close up....

:---[===] *

[orin stepanek]

M20_volskiy1024.jpg

Oh, don't you wish that you could see these with the naked eye?

[neufer]

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Explanation: The beautiful Trifid Nebula, also known as Messier 20, is easy to find with a small telescope in the nebula rich constellation Sagittarius. Trisected by dust lanes the Trifid itself is about 40 light-years across and a mere 300,000 years old. That makes it one of the youngest star forming regions in our sky, with newborn and embryonic stars embedded in its natal dust and gas clouds.

<<The Venus of Willendorf is an 11.1-centimetre-tall Venus figurine estimated to [be a mere 30,000 years old]. It was found on August 7, 1908 by a workman named J. Veran during excavations conducted by archaeologists Josef Szombathy, Hugo Obermaier and Josef Bayer at a paleolithic site near Willendorf, a village in Lower Austria near the town of Krems. It is carved from an oolitic limestone that is not local to the area, and tinted with red ochre. The figurine is now in the Naturhistorisches Museum in Vienna, Austria. Catherine McCoid and LeRoy McDermott hypothesize that the figurines may have been created as self-portraits by women. This theory stems from the correlation of the proportions of the statues to how the proportions of women's bodies would seem if they were looking down at themselves, which would have been the only way to view their bodies during this period. They speculate that the complete lack of facial features could be accounted for by the fact that sculptors did not own mirrors. This reasoning has been criticized by Michael S. Bisson, who notes that water pools and puddles would have been readily-available natural mirrors for Paleolithic humans.>>

Art Willendorffer