Radial filter is convenient, but worth considering whether the paint brush is a better tool for the job. Consider using a big brush and turn flow up to 100 so effect is fully applied in one stroke (or minimum number of strokes) without the brushing uneven-ness which comes from going over an area repeatedly at reduced flow *** see note below.
The bottom line: unless an evenly feathered elipse-shaped mask is precisely what you want, you can get superior results using the brush, if you have the requisite brushing skill, granted - maybe not as convenient...
PS - I used a (smaller) radial filter over the moon (and surrounding glow (but not over the darker sourrounding sky)) in my 2nd whack, just for convenience (and for fun, since it's new).
Tip: if you are unsure just how you want the paint, use a radial filter at first, move it around, change it's size and shape (and feathering), until you get something about right, or in any case you learn something, then if not exactly right, delete it and apply paint with brush instead, armed with additional knowledge experience of what you want..
*** Note: Unlike some "airbrush-like" tools in some editors, 'Flow' in Lr does NOT control amount of paint per unit time, it controls amount of paint per stroke, so "mid-stroke hesitation" etc. will not affect result.
UPDATE: Upon review, I stand corrected: I used three radial filters over the moon. - probably should have just used paint brush.
Cheers,
Rob
Message was UPDATED by: Rob Cole