August 4th APOD: M46 starfield. A very red star.

[Hirusan]

If you look at the very center of the image after zooming in, you'll see a very red star. I'm wondering if this is just a camera artifact. It's really red. I'm wondering if anyone can tell me why this star is so red?

[Empeda]

Star colours depend on their stellar classification - which, to simplify things a little has a lot to do with their temperatures.

Basically stars have different classifications - O, B, A, F, G, K, M with O being the hottest and M being the coolest (you can remember this by 'Oh Be A Fine Girl(Guy) Kiss Me', it's somewhat random due to historical reasons).

Our star is a G-type star, which has a surface temperature of around 5000/6000 degrees. This temperature means that the sun looks yellow/orange.

A cooler star, such as an M-type, will have a cooler surface temperature (around 2500-3000 degrees I think - I'm recalling all these figures from memory so they might not be 100% accurate), and will appear red. The hotter stars, the Os and the Bs, are so hot that they appear blue/white in colour.

Now this is true for 'Main Sequence' stars, i.e. those that have 'matured', or in adulthood if you like. Things get a little more complex when you take into account dying stars - for example, when the Sun's hydrogren content depletes enough and it starts to die - it'll swell up into a red giant, and be..well...red (again, due mainly to the cooler surface it will have).

So to actually finally answer your question(!), the star that you see is either a small, cool main sequence dwarf star (a type M) or an old star that has become a red giant.

Hope this helps (and is reasonably accurate!).

[Hirusan]

I am aware of the different classes of stars. This star, however, is really really red. I'd like to point it out somehow. It's the reddest star out of all of them. It's in teh upper middle left area as you near the planetary nebula. It seems more like a imagining artifact more than a star, but I could be wrong.

[Empeda]

Can't see anything out of the ordinary - if you want download the picture, put it in paint, slap a whopping great arrow on it and email it to me - like I say I'm no expert but I'm interested to find out what you're seeing....

[lllbr0kenlll]

provided we are looking at the same thing....
i think thats prolly a defect..
cause, thats very red...like fire engine red
crazy picture huh?

[makc]

...if you want download the picture, put it in paint, slap a whopping great arrow on it... I'm interested to find out what you're seeing....

I think it's this:


but see original image for better quality. Also, I've just noticed there another very red star along with very green one (now marked). It's all very blurred in my screenshot, so you probably won't see it - check goddamn original.

[Hirusan]

Yes! you have it. It's the one on the left. Although I'm noticing that the other one that you circled are just as red. You can't really see them on the close up, so reference it with the other stars and you'll see what I mean by just how red they are.

I also noticed that you won't find any other stars like those in the entire star field.

[William Roeder]

And what is the green, red, and white donut in the upper left corner

[lllbr0kenlll]

i think some type of eclair

that'd be a nebula

[Empeda]

The donut is a planetary nebula - see the description with the picture:

http://apod.gsfc.nasa.gov/apod/ap050804.html

As for the bright red dots - I think it that they probably are stars, but the way in which the device photographed the scene probably made them that red - that's my guess incidently, I don't really know!