Star question

[Clarry]

Someone asked me the other day if all the stars we can see in our sky are from our own galaxy, ie, The Milky Way. I said yes, but is that right? Sure we can see other galaxies from earth, but only clearly with the aid of a telescope.
I was right wasn't I?

[renormalised]

You're correct.

[ngcles]

Hi Clarry,



Yep. In fact the overwhelming majority of the ones you can see as individuals are closer to the Sun than 2,500 light-years which is about 4% of the diameter of the Milky Way. There are some further than this but not many. Off the top of my head, five that are further than 2,500 that can be seen naked eye are Eta Carinae, AG Carinae (very occasionally) and Kappa Crucis (assuming it is part of the Jewel Box cluster and not in the foreground) (which is possible).

Of the quite bright stars (ie brighter than 2nd magnitude), the most distant I believe is Deneb (Alpha Cygni) assuming the most often quote distance of 2,500 ly is correct -- though it may be closer. Magnitude 3.8 Mu Sagittarii (between M8 & M24) is believed to be 3,600 ly distant. There are probably some few others but that's it off the top of my head. AG Carinae is probably the winner (when it very occasionally becomes visible to the naked eye) at about 20,000ly. It is a Luminous Blue Variable Hypergiant probably in transition to becoming a Wolf-Rayet.

It is possible that a few of the stars you can see naked eye, while current members of the Milky Way, originated in another galaxy before being captured in past galaxy mergers. Fred Watson is working on a project at the moment that might identify some and is likely to give us a much clearer picture about which stars are related to which other stars in our neighbourhood and the past history of our part of the Milky Way.


Best,

Les D

Edit: And a few more I dug up quickly. N.B the distances are estimates because over 2,500ly, there is no way to directly measure the distance of these stars:

S Monocerotis mag 4.2var Distance 2,500ly

X Persei mag 6.1var Distance 2,700ly

Alpha Camelopardalis mag 4.3 Distance 4,000ly

Rho Leonis mag 3.8 Distance 4,000ly

Mu Normae mag 4.9 Distance 4,660 ly

Chi Orionis mag 4.6 Distance 4,900ly

6 Cassiopeiae mag 5.4 Distance: 8100ly

Rho Cassiopeiae mag 4.5 Distance 10 000 ly

So there you go ...

[Enchilada]

You are 100% correct - assuming you mean naked-eye stars.

The only example where this is not true was the supernova SN 1987A (LMC) and S Andromedae / also SN 1885A, in the Andromeda Galaxy. Both reached 2nd magnitude or so.

[Clarry]

Thanks folks, that's what I thought.

[renormalised]

Yes there is, Les. I have a large tape measure we can use, so let's get to it:P:P:P:D:D:D

[mithrandir]

Have you tried to get it listed by Guinness? "World's Longest Tape Measure":rofl:

[ngcles]

HI Carl,



No worries. :thumbsup:

Tell you what, I'll go and make us a cut-lunch and a thermos for the trip if you can organise the other requirements ... :P


Best,

Les D

[renormalised]

Done:thumbsup::P:D:D

[renormalised]

Yeah, but they wouldn't enter it...it was too big for the edition:P:P:D:D