I created this earth using cycles can anybody tell me how to add a glow effects to it and also if anything could be done to make it better.
Disclaimer: I just learned this myself, so @NoviceInDisguise can edit it if needed.
Create a bright point of light in your scene. This would be planet earth- already created in your case. Glare can't happen without a target.
Render the image.
At the top of your screen, change the screen layout mode to be compositing. Once done, you may need to check a little box in the node editor that says use nodes.
Add a glare filter between the image input and the finished output. Optionally you may add a viewer node at the end of the string so you can see the image in the node editor. In order for a viewer node to be active, you need to check Backdrop. It's located near use nodes.
Set the glare mode to fog glow.
Mess with the settings on the glare node until you have a perfectly glowing planet.