10
$\begingroup$

Today, here in Brazil, I have observed (and is still observing) an interesting phenomenon.

The Moon is near to a big star in the sky, but this is normal. The interesting part is what's around them.

A huge circle in which the moon and the star is inside. Why does this circle appear? What is it?

(This isn't a cloud. It looks like more something like a light reflection of a lamp.)

Unfortunately, I hadn't a good camera to catch this. I would appreciate having an image posted for this.

$\endgroup$
1
  • 2
    $\begingroup$ Not so normal, check some ephemerides table, I believe that the star was to be Jupiter. $\endgroup$
    – arivero
    Dec 7, 2011 at 2:14

1 Answer 1

13
$\begingroup$

You might be describing a moon aura.

Moon Aura

It's caused by diffraction on tiny ice crystals in the atmosphere: When the moonlight hits the ice, you get interference effects that depend on the angle of the incident light. The idea is similar to powder diffraction in crystallography.

$\endgroup$
4
  • $\begingroup$ Yes. It's was I'm looking for. $\endgroup$
    – GarouDan
    Dec 7, 2011 at 12:10
  • $\begingroup$ Thx about the explanation! $\endgroup$
    – GarouDan
    Dec 7, 2011 at 12:10
  • 1
    $\begingroup$ to expand a little, the crystals are flat but sit in the same orientation and diffract the light through 23 degrees (I think!) $\endgroup$
    – Nic
    Dec 7, 2011 at 12:30
  • 2
    $\begingroup$ Also known as "lunar halo" en.wikipedia.org/wiki/… . $\endgroup$
    – jbatista
    Dec 10, 2011 at 0:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.