APOD: The Orion You Can Almost See (2019 Aug 21)

[APOD Robot]

The Orion You Can Almost See

Explanation: Do you recognize this constellation? Although it is one of the most recognizable star groupings on the sky, this is a more full Orion than you can see -- an Orion only revealed with long exposure digital camera imaging and post-processing. Here the cool red giant Betelgeuse takes on a strong orange tint as the brightest star at the lower left. Orion's hot blue stars are numerous, with supergiant Rigel balancing Betelgeuse on the upper right, and Bellatrix at the upper left. Lined up in Orion's belt are three stars all about 1,500 light-years away, born from the constellation's well-studied interstellar clouds. To the right of Orion's belt is a bright but fuzzy patch that might also look familiar -- the stellar nursery known as Orion's Nebula. Finally, just barely visible to the unaided eye but quite striking here is Barnard's Loop -- a huge gaseous emission nebula surrounding Orion's Belt and Nebula discovered over 100 years ago by the pioneering Orion photographer E. E. Barnard.

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[Ann]

This is a fantastic picture that brings out Orion in more than its full glory.

Ann

[hamilton1]

The description says the Belt stars are all about 1500 LY away, but according to Jim Kaler's 'Stars' Alnilam is 1.5 times farther away than the other two -

http://stars.astro.illinois.edu/sow/alnilam.html

I've seen that discrepancy on other sites too.

[orin stepanek]

I'm sure that each star in Orion is a different distance from us!

[Ann]

The description says the Belt stars are all about 1500 LY away, but according to Jim Kaler's 'Stars' Alnilam is 1.5 times farther away than the other two -

http://stars.astro.illinois.edu/sow/alnilam.html

I've seen that discrepancy on other sites too.

The reason for the discrepancy is the Hipparcos parallax, which is noticeably smaller for Alnilam than for the other two Belt stars. A star's parallax is its apparent motion back and forth in the sky as the Earth moves around the Sun. The smaller the parallax, the more distant is the star.

The reason why we would doubt the suggestion that Alnilam is much farther away than Alnitak and Mintaka is that all three stars look pretty much equally bright to our eyes and are also lined up rather close to one another. Moreover the three stars belong to similar sprectral classes. It would be a strange coincidence if three so similar-looking stars of similar spectral classes which are lined up so relatively close together were at very different distances from us.

The Hipparcos parallaxes are not very reliable for stars that are more than, say, 500 light-years away. The Belt stars are certainly farther away than 500 light-years, so when Hippacos said that Alnilam is twice as far away as Alnitak and Mintaka, we must take that statement with a grain of salt.

Ann

[khjalmarj]

Didja notice you can, if you zoom in sufficiently, make out the Horsehead? I think this is the first time I've seen that in a wide-angle photo. Gorgeous!

[neufer]

Didja notice you can, if you zoom in sufficiently, make out the Horsehead?

I think this is the first time I've seen that in a wide-angle photo. Gorgeous!

Compare it against Williamina Fleming's 1888 photo and tell us if anything has changed.

Negative Plate B2312 : February 6th, 1888

---

<<Plate B2312 was taken February 6th, 1888 with the 8-inch Bache Doublet in Cambridge. It covers a familiar region of the sky: Orion’s Belt with Orion’s Nebula defined in the center. Williamina describes an object under the first star of Orion’s Belt: “A large nebulosity extending nearly south from Zeta Orionis for about 60 minutes. More intense and well marked on the following side, with a semicircular indentation 5 minutes in diameter 30 minutes from Zeta.” (Annals of the Harvard College Observatory, Vol 18 (1890), 116)

The “semicircular indentation” refers to the Horsehead Nebula, recognizable by the ‘notch’ that seems to fall over itself. Of course, it’s more helpful (but somewhat redundant) to say it looks like a horse’s head. Visit the plate information page on the DASCH website to learn more about this plate.>>

[bystander]

I'm surprised Saiph (κ Ori, the foot opposite Rigel)) isn't labeled. It's a part of what makes Orion recognizable and is the sixth brightest star in Orion.

[TrickyGlow]

The Orion Nebula looks like it is morphing out of the gas for some reason, probably due to a blackhole within the ultrabright area i assume.

[Ann]

I'm surprised Saiph (κ Ori, the foot opposite Rigel)) isn't labeled. It's a part of what makes Orion recognizable and is the sixth brightest star in Orion.

Click to view full size image

Indeed, Saiph is an important part of the Orion constellation.

Unfortunately I don't know the author of the picture at right.

Ann

[Boomer12k]

Awesome image...very vivid...

I had gotten a copy of "Barnard's Handbook", it is a loose leaf notebook and thick. I was suppose the have gotten a second volume, but they had a fire at the time... I think I have some updated paperback version of those...I am not sure... and it is too hard to go poking around to find them...

:---[===]*

[Ann]

Awesome image...very vivid...

I had gotten a copy of "Barnard's Handbook", it is a loose leaf notebook and thick. I was suppose the have gotten a second volume, but they had a fire at the time... I think I have some updated paperback version of those...I am not sure... and it is too hard to go poking around to find them...

:---[===]*

You don't mean "Burnham's Celestial Handbook", do you, Boomer?

There are three volumes of this handbook. These books are really quite old, but there are some nice old photographs in them! Check out what it says about Orion (in Volume #2) and note how faint Betelgeuse looks in those photos, though not as faint as in the very old photo (by Pickering?) that I posted earlier in this thread.

Ann

[hamilton1]

The description says the Belt stars are all about 1500 LY away, but according to Jim Kaler's 'Stars' Alnilam is 1.5 times farther away than the other two -

http://stars.astro.illinois.edu/sow/alnilam.html

I've seen that discrepancy on other sites too.

The reason for the discrepancy is the Hipparcos parallax, which is noticeably smaller for Alnilam than for the other two Belt stars. A star's parallax is its apparent motion back and forth in the sky as the Earth moves around the Sun. The smaller the parallax, the more distant is the star.

The reason why we would doubt the suggestion that Alnilam is much farther away than Alnitak and Mintaka is that all three stars look pretty much equally bright to our eyes and are also lined up rather close to one another. Moreover the three stars belong to similar sprectral classes. It would be a strange coincidence if three so similar-looking stars of similar spectral classes which are lined up so relatively close together were at very different distances from us.

The Hipparcos parallaxes are not very reliable for stars that are more than, say, 500 light-years away. The Belt stars are certainly farther away than 500 light-years, so when Hippacos said that Alnilam is twice as far away as Alnitak and Mintaka, we must take that statement with a grain of salt.

Ann

It's also quite a coincidence that the nebulosity surrounding the Pleiades has nothing to do with the Pleiades, but I take your point.

[Ann]

It's also quite a coincidence that the nebulosity surrounding the Pleiades has nothing to do with the Pleiades, but I take your point.

It's not quite the same thing. The bright stars of the Pleiades are indeed at the same distance as the nebulosity they are immersed in. Of course, the current co-habitation of the stars and the dust cloud is just a chance encounter.

Ann

[Loaidaaort]

Hi everyone! I'm pretty new to this online thing so please bare with me... I am not familiar with this subject although, once I've got the terminology down pat I will be able to have more in-depth discussions with everyone. For as of right now my feedback is that this photo is very detailed, very beautiful and vivid.