Starship Asterisk*

hamilton1 wrote: ↑Wed Aug 21, 2019 10:06 am 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.

khjalmarj wrote: ↑Wed Aug 21, 2019 1:38 pm
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!

http://altbibl.io/gazette/the-first-computer-williamina-fleming-and-the-horsehead-nebula/ wrote:

Negative Plate B2312 : February 6th, 1888

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<<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 wrote: ↑Wed Aug 21, 2019 4:46 pm 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.

Boomer12k wrote: ↑Thu Aug 22, 2019 12:21 am 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...

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Ann wrote: ↑Wed Aug 21, 2019 11:21 am

hamilton1 wrote: ↑Wed Aug 21, 2019 10:06 am 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

hamilton1 wrote: ↑Thu Aug 22, 2019 9:27 am
It's also quite a coincidence that the nebulosity surrounding the Pleiades has nothing to do with the Pleiades, but I take your point.