I’m not sure if this falls under lighting (I think it does).
I’m trying to create a sun object (not a lamp) by creating a sphere that emits, but whenever I render it, I don’t see light rays, just a big yellow ball with very obvious edges. How can I make my object emit light rays as well as light so it looks like a sun instead of a ball?
this is done via the composting node using either a glare node or a sun beams node.
introduction to the compositor - http://www.blenderguru.com/tutorials/introduction-to-the-compositor/
compositor tutorials - http://blenderdiplom.com/en/tutorials/compositing.html
what compositor nodes do - http://archive.blender.org/development/release-logs/blender-246/compositing-nodes/index.html
Tutorial on using passes - https://cgcookie.com/blender/2012/12/10/compositing-cycles-render-passes-blender/
Is there a way to get this on only one object?
The effect you’re trying to create comes from light scattering through the atmosphere (in space, the sun is actually just a ball of light with hard edges unless you’re using a lens that would introduce glare and flares). You could try making the sun a flat plane with a spherical gradient on it to give the impression of glare (it won’t interact well with anything overlapping the light though), but other than that your best bet is nodes (unless you want to try to actually set up a to-scale atmosphere with realistic light scattering using a volumetric object I guess, if you really want to make your scene about sixty miles tall and spend a long time getting the settings right and hoping Blender’s volumetric rendering supports realistic light scattering)