Thing about shininess...colour fidelity varies from screen to screen, so what appears bright on one screen can be very dark on another. This I find, is the single biggest disadvantage on doing art on a computer- if you're finicky about the lighting levels you'll never be happy.

Fortunately one can adjust the levels if need be.

Oh yes, that is sooo very true...
*adjusts*

Actually tell you what, if you could show me what you think is acceptable on your screen, then show me and we can compare!

Okay, I spent some 10 minutes on playing with it~
Couldn't play with the layers, but thanks to lasso tool and smudge, I think it looks okay.

As you may notice, I interpreted the 'shine' more as clouds, and therefore added a swirl in them...

But shortly, this looks good on my screen with that lighting.

I do like the treatment of the cloud as it appears more appropriate for the cartoony Earth.

But...you used a hard edge on the paintbrush didn't you. The way my screen is, I can see an outline in the background shine!

Can you?

Didn't use the paintbrush.
If the edge you're talking about is the one next to the stars in the upper left corner, it's because I forgot to smudge the transition from the area I had selected and changed.
So if it's that one, hold on a minute and I'll update it!

Ah, not just the upper left but also the lower right, just under the meteor.

Awahh, so finicky!!!!!

Got it!
Corrected!
Any more?

Is a bit difficult when I don't have layers. :P

I'm guessing a soft brush with adjusted opacity. Or at least that would be able to do those things. I smudged in my version, both in the length of the comet and the surface of the clouds~
A dodge brush could probably do the same thing...

But I'm not sure what Strop did, he tends to use slightly more complicated methods than I would guess~