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I was looking at information about the Horsehead nebula on wikipedia

http://en.wikipedia.org/wiki/Horsehead_nebula

and it says that its apparent dimensions are 8x6 arcmins.

I'm not sure how to find the actual dimensions, say in light-years. Here's how I believe it should be, but I'm sure I'm wrong.

According to wikipedia, the nebula is 1500 ly away. 1 arcmin = 1/60 degrees. So the dimensions should be:

1500*tan(8/60) by 1500*tan(6/60), which is 3.5 ly by 2.6 ly.

Have I got it right, or have I missed something obvious.

Thanks,

Maria