Starship Asterisk*

I am new to this site and could not find a forum for dumb questions. I am a professional phoographer and understand perspective and focal lengths of lenses but I am having trouble understanding most galactic photos and the star or galactic fields around them. Is the field around them always other galaxies in the background or are there stars between the galaxie and the lens? It seems to me that any star between would be too huge and obviously a galaxie would be even larger so all "stars" in the photo would have to be galaxies, is this true? Thanks

I have noticed that, in general, most local foreground stars tend to have diffraction spikes sorrounding them and that most (all) galaxies do not display them. (Although some images are "Scrubbed" to remove the spikes).

But, my point is that any star in our galaxy, it seems to me, would appear to be as big as any distant galaxy, more or less of course, when looking through an earth bound telescope; therefore the "stars" in the field around a close view of a distant galaxy would surely be galaxys that are even further distant, right?

Hi,

Stars are virtually point sources, due to their distance. Only a very few huge stars like Betelgeuse have had their diameters measured. This is the result of something on the order of 200,000 miles across at an enormous distance -- even the nearest stars at 4 LY or 12 trillion miles are extremely tiny visually. Ground based telescopes struggle to get 1 arcsecond per pixel, and the star images are realistically a few thousandths of that size, therefore the star images are less than a pixel across. Star images often LOOK larger because their light overflows the sensors and spreads out, but in fact the stars themselves are undetectably small disks.

Galaxies are are much larger distances, sure. Millions of times further away. But they're also billions of times larger than stars. The ones we can get detailed images of are from 1 to 100 million LY away, but they're also 50,000 to 200,000 LY across, so their images are between 10 and 3000 arcseconds across.

So, a galaxy call fill our field of view, while stars in our own galaxy are too small to see any details at all.

It's just a matter of numbers.

thanks Scott, that answered my question. I didn't realize that the galaxies would appear to be that much bigger than a star in our galaxy at those massive distances. That has bugged me quite a while.