Stellar Heirarchies

[_MackTuesday_]

If you go out about 20 light years and turn around, you'll see that Procyon, Sirius, Alpha Centauri, and Sol form a quartet. These four stars are the big boys in our little neighborhood.

This got me interested in studying the relative positions of the brighter stars in the vicinity of Sol and Sirius. The little Ms and most of the Ks are so abundant and dim that they're not as interesting to me.

I had the idea of developing a heirarchy of stars. A star's superior in the heirarchy is the brightest star in its sky that is also more luminous. So Sirius is our superior in the heirarchy. Procyon is the brightest star in Sirius' sky, but it isn't as luminous; Canopus is the next brightest from Sirius' point of view and it's also more luminous, so it is Sirius' superior.

It turns out that Sirius is a local boss. Fellow members of our group include Epsilon Eridani, Keid, and Tau Ceti. Vega, Fomalhaut and Pollux are also nearby bosses. Altair, 61 Cygni, and 70 Ophiuchi belong to Vega. Rho1 Cancri and 11 Leonis Minoris belong to Pollux. No "big name" stars belong to the Fomalhaut group.

Canopus dominates our district. It's over 300 light years away but claims many nearby stars, like Barnard's Star and Epsilon Indi.

The stars of Ursa Major constitute a large complex.

I went through a number of the nearby bright stars and made a new asterisms file that illustrates these heirarchies. I had to do it by hand because I couldn't find a specification of Celestia's stars.dat file format. It might be interesting to see the complete heirarchy.

I have some screenshots and the asterisms file right here but I just realized I don't have any way to upload the files to my website from this machine. I'll add them soon. Does anyone even find this interesting?

[Evil Dr Ganymede]

Dunno about "interesting" since I'm not sure whether one can get anything that's actually useful out of it, but I do think it's an intriguing concept. Put me down as curious and listening

[selden]

The stars in Ursa Major are part of a nearby open cluster known as "Collinder 285" or the "Ursa Major Moving Cluster." In other words, astronomers do tend to find such things interesting They can provide hints as to how stars form and how their associations change with time.

I'm guessing that many of the visual associations that Mack is finding are just coincidence, though. One also has to compare the motions and compositions of the stars in order to try to find out if they're actually related to one another or just temporary neighbors.

[ElPelado]

I heard a couple of times that our Sun may be a part of the cluster of the Ursa mayor... is it true or not?

[selden]

ElPelado,

Studies of the stars in the cluster Collinder 285 show that it is less than 800 million years old, but our sun is more than 5 times that age. Also, the cluster's members are travelling past us at an average speed of about 46 km/sec.

In other words, no, it's not part of the Ursa Major cluster. We just happen to be travelling past or through the cluster now.

See http://www.seds.org/messier/xtra/ngc/uma-cl.html

[_MackTuesday_]

Here are the goods.

Here is the asterisms file: http://www.mat.ucsb.edu/~brent/asterisms.dat


This is a screen shot of the Sirius group as seen from the Earth. Alpha Centauri appears in the lower left corner. Sol is the bright star near the top. The line connecting Sol to Sirius is not visible. The line appearing to radiate toward Sol is actually pointing off into the distance. I'm sure I remember correctly but I think it goes to Ross 614.

http://www.mat.ucsb.edu/~brent/SiriusGroup.jpg


This shows the position of Canopus relative to the stars I studied. As you can see it's far away, but even at that distance it is the direct superior of many of the stars near to us.

http://www.mat.ucsb.edu/~brent/Canopus.jpg


This image illustrates Collinder 285, the large association that makes up Ursa Major. On the left is Capella. It was interesting to find that Castor and Pollux are not the brightest in each others' skies, despite their proximity to each other. Capella is their superior.

http://www.mat.ucsb.edu/~brent/AurGemUMa.jpg


I do realize that these heirarchies will change as time goes by. This model has done its job, though, which was to help me get a grasp of relative positions of the nearby stars in space.

By the way, while I was doing this I noticed that the Pleiades looks elongated from the side. It seems more likely to me that this group is roughly spherical in distribution, and that our uncertainty about the distances of the individual stars has had the effect of scattering their positions radially (with respect to Earth) in Celestia. I doubt anything can be done about it, though.

[_MackTuesday_]

I previewed my post twice but still made a mistake. I meant to say, "I'm not sure I remember correctly but I think it goes to Ross 614."

[selden]

Mack,

If you register with the server, you'll be able to edit your posts. Registering with Celestia's Web forum software does not require you to provide any personal information at all.

[Matt McIrvin]

By the way, while I was doing this I noticed that the Pleiades looks elongated from the side. It seems more likely to me that this group is roughly spherical in distribution, and that our uncertainty about the distances of the individual stars has had the effect of scattering their positions radially (with respect to Earth) in Celestia. I doubt anything can be done about it, though.

This is a common problem in the 3D mapping of astronomical objects. The people who map galaxies by redshift call it "the Finger-of-God effect" because the uncertainty caused by galaxies' peculiar velocities makes it look like big superclusters are all elongated and pointing toward Earth.