M13 – Globular Cluster in Hercules


M13 is a favorite subject for many observers, myself included.  I’ve looked at it from the backyard with my own eyeball.  I’ve seen it through my 8×50 binoculars.  I’ve looked at it in a Dobsonian with a photomultiplier.   This globular cluster contains over 100,000 stars that are all held in this fuzzy ball by the weak force that sucks.  Gravity.  From studying the spectral lines of various stars and the red shift of those stars scientists have derived an approximate distance of 25,100 light years from Earth.  It has an angular size of 20 arc minutes or 1/3rd of a degree.  One degree is 60 arc minutes, 1 arc minute is 60 arc seconds.  At a distance of 25,100 light years that means the globular cluster itself is 145 light years wide.  Keep in mind that light travels the same distance as seven and a half times the circumference of the Earth every second.  It takes about 8 minutes for light from the Sun to get to earth.  Light leaving one side of the Hercules Cluster will take 145 years just to get to the other side of it.  It will take another 25,000 years to reach your eyeball.  Huge, HUGE distances and this is a relatively close object.  In looking at M13 over the years I never seem to stop enjoying this object.

I took this image with my 6″ Meade Schmidt-Newtonian reflector on a LXD-75 mount.  It was autoguided with a Meade DSI Pro and imaged with an unmodified Canon Digital Rebel.  I used some really clever free software to stack 71 subexposures of 30 seconds and after some processing got this image.  The process of stacking adds data together in a magical way to increase the signal without radically increasing the background noise level.  If I were a mathematician I could explain it to you but I’m sure you’d fall asleep.  I sure would.  After stacking I typically run the resulting image through yet more software to increase the contrast, brighten things up and enhance the color.  It seems I always spend more time processing the image than taking it but that’s honestly half of the fun.  In the end, what you see is what you get.  I sure had fun taking it.  I hope you have fun enjoying it.

UrbanAstronomy.com v1.1

My mission is to get people in urban areas to think about what’s in the sky above them. Just because you’re in the city doesn’t mean the stars don’t exist or that you can’t see or understand really cool celestial events.