APOD: North of Orion's Belt (2020 Nov 05)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 4107
Joined: Fri Dec 04, 2009 3:27 am

APOD: North of Orion's Belt (2020 Nov 05)

Post by APOD Robot » Thu Nov 05, 2020 5:05 am

Image North of Orion's Belt

Explanation: Bright stars, interstellar clouds of dust and glowing nebulae fill this cosmic scene, a skyscape just north of Orion's belt. Close to the plane of our Milky Way Galaxy, the wide field view spans just under 5 degrees or about 10 full moons on the sky. Striking bluish M78, a reflection nebula, is at the lower right. M78's tint is due to dust preferentially reflecting the blue light of hot, young stars. In colorful contrast, the red swath of glowing hydrogen gas streaming through the center is part of the region's faint but extensive emission nebula known as Barnard's Loop. At upper left, a dark dust cloud forms a prominent silhouette cataloged as LDN 1622. While M78 and the complex Barnard's Loop are some 1,500 light-years away, LDN 1622 is likely to be much closer, only about 500 light-years distant from our fair planet Earth.

<< Previous APOD This Day in APOD Next APOD >>

User avatar
Ann
4725 Å
Posts: 10908
Joined: Sat May 29, 2010 5:33 am

Re: APOD: North of Orion's Belt (2020 Nov 05)

Post by Ann » Thu Nov 05, 2020 7:23 am

Two nebulas are of interest in today's APOD (in my opinion): Bright reflection nebula M78 and dusty starforming pillar LDN 1622.

M78 with dark dust lane.png
Reflection nebula M78 with dark dust lane. Photo: Terry Hancock.
M78 is said to be the easiest-to-spot reflection nebula in the sky. Why is it so bright? I'd say it's because of the dark dust lane that frames it. Note how the very brightest part of M78 is situated right next to a very dark dust lane. It must be the contrast between dark and light that makes this nebula so visible. Note that another reflection nebula "above" M78 has no dark dust lane to outline it. That reflection nebula is probably almost (or totally) impossible to spot visually.



Dark pillar LDN 1622 in Orion.png
Dusty starforming pillar LDN 1622. Photo: Terry Hancock.










LDN 1622 is a starforming pillar, because we can see a star forming at the tip of it (just below center right). We can also see that it is a cosmic pillar, because it is dusty and elongated, which is what we expect from windswept dust structures being eroded by strong stellar winds from hot bright stars. Fascinatingly, it is elongated from lower right to upper right, which is to say that it is "pointing" in the general direction of Orion's Belt and the hot bright stars Alnitak, Alnilam and Mintaka. But in this general direction we also find Sigma Orionis, which is responsible for sculpting the Horsehead Nebula.



Closeup LDN 1622 Volskiy.png
The LDN 1622 region in Orion. Photo: Stanislav Volskiy.
Note in the picture at left that LDN 1622 (arrowed) is elongated in such a way that it is pointing in the general direction of Orion's Belt, Sigma Orionis and the Horsehead Nebula. (The Horsehead nebula is barely visible as a tiny dark protrusion near the bottom edge of the picture close to 6 o'clock (closer to 5.30). Orion's Belt and Sigma Orionis are bright blue stars near bottom right.

M78 is located on the inner side of broad red Barnard's Loop, while LDN 1622 is on the outside of if. You could actually draw an almost straight line from LDN 1622, to M78, to the Horsehead nebula, and find that these three nebulas are at (apparently) equal distances from one another.

The appearance of LDN 1622 suggests to me that it is actually being sculpted by stellar winds from Orion's Belt or Sigma Orionis.









So the point I'm trying to make is that LDN 1622 looks pretty much like a dusty starforming pillar that is being sculpted and eroded by stellar winds from either the bright stars of Orion's Belt, or, perhaps even more likely, by stellar winds from Sigma Orionis. But today's caption does not agree with me:
APOD Robot wrote:

While M78 and the complex Barnard's Loop are some 1,500 light-years away, LDN 1622 is likely to be much closer, only about 500 light-years distant from our fair planet Earth.
Note in the picture by Stanislav Volskiy that LDN 1622 appears to be located at the bottom of the "wake" that has apparently been left by Betelgeuse, which is in fact a runaway star:
Wikipedia wrote about Betelgeuse:

Having been ejected from its birthplace in the Orion OB1 Association—which includes the stars in Orion's Belt—this runaway star has been observed moving through the interstellar medium at a speed of 30 km/s, creating a bow shock over four light-years wide.
But I don't think that Betelgeuse has anything to do with LDN 1622. This dark dusty pillar is elongated in the wrong direction to have been sculpted by Betelgeuse.

Ann
You do not have the required permissions to view the files attached to this post.
Color Commentator

VictorBorun
Ensign
Posts: 20
Joined: Fri Oct 16, 2020 10:25 pm

Re: APOD: North of Orion's Belt (2020 Nov 05)

Post by VictorBorun » Thu Nov 05, 2020 7:45 am

can a dark dusty pillar last 10 million years to drift a thousand ly away from the star that sculpted it?

VictorBorun
Ensign
Posts: 20
Joined: Fri Oct 16, 2020 10:25 pm

Re: APOD: North of Orion's Belt (2020 Nov 05)

Post by VictorBorun » Thu Nov 05, 2020 7:57 am

I wish we had somethinng better than GAIA to gauge a star's distance from us.
Say some way to imply a star's angle diameter from weak blinking caused by interstellar gas fluctuations or rogue planetoids nanolensing

User avatar
Ann
4725 Å
Posts: 10908
Joined: Sat May 29, 2010 5:33 am

Re: APOD: North of Orion's Belt (2020 Nov 05)

Post by Ann » Thu Nov 05, 2020 7:58 am

VictorBorun wrote:
Thu Nov 05, 2020 7:45 am
can a dark dusty pillar last 10 million years to drift a thousand ly away from the star that sculpted it?
No, I really don't think it can.

Ann
Color Commentator

User avatar
Ann
4725 Å
Posts: 10908
Joined: Sat May 29, 2010 5:33 am

Re: APOD: North of Orion's Belt (2020 Nov 05)

Post by Ann » Thu Nov 05, 2020 10:22 am

VictorBorun wrote:
Thu Nov 05, 2020 7:57 am
I wish we had somethinng better than GAIA to gauge a star's distance from us.
Say some way to imply a star's angle diameter from weak blinking caused by interstellar gas fluctuations or rogue planetoids nanolensing
The main reason why Gaia can't measure the distance to Betelgeuse is that Betelgeuse is far too bright for Gaia. Gaia was constructed to measure the distance to a billion stars, most of which look extremely faint in the Earth's sky. Down to, I guess, 18th magnitude or something. (I'm too lazy to google it.)

Betelgeuse, by contrast, is normally a first magnitude star and normally the eleventh brightest star in the sky.

Ann
Color Commentator

BDanielMayfield
Don't bring me down
Posts: 2523
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: North of Orion's Belt (2020 Nov 05)

Post by BDanielMayfield » Thu Nov 05, 2020 5:17 pm

Ann wrote:
Thu Nov 05, 2020 10:22 am
VictorBorun wrote:
Thu Nov 05, 2020 7:57 am
I wish we had somethinng better than GAIA to gauge a star's distance from us.
Say some way to imply a star's angle diameter from weak blinking caused by interstellar gas fluctuations or rogue planetoids nanolensing
The main reason why Gaia can't measure the distance to Betelgeuse is that Betelgeuse is far too bright for Gaia. Gaia was constructed to measure the distance to a billion stars, most of which look extremely faint in the Earth's sky. Down to, I guess, 18th magnitude or something. (I'm too lazy to google it.)

Betelgeuse, by contrast, is normally a first magnitude star and normally the eleventh brightest star in the sky.

Ann
What you wrote about Gaia’s bright star limitations was true as the mission was being planned, however once this observatory was in space the operators learned ways of overcoming this limitation. Note what Wikipedia’s article on Betelgeuse says:
Although the European Space Agency's current Gaia mission was not expected to produce good results for stars brighter than the approximately V=6 saturation limit of the mission's instruments,[94] actual operation has shown good performance on objects to about magnitude +3. Forced observations of brighter stars mean that final results should be available for all bright stars and a parallax for Betelgeuse will be published an order of magnitude more accurate than currently available.[95] There is no data on Betelgeuse in Gaia Data Release 2.[96]
Perhaps Betelgeuse’s recent period of dimming has helped too. In any case, we can still expect an improved distance estimate for this star from Gaia.
Just as zero is not equal to infinity, everything coming from nothing is illogical.