What is the white halo in my eyepiece?

[bigglesdad]

Hi all. I have noticed a white halo or circle around bright objects when I look at bright stars etc. It doesn't always happen, but I'd like to know what causes it and is there something I can use to stop it? Many thanks.

[Merlin66]

Could be anything from atmospheric conditions to dust and moisture on your optics/eyepieces.

Netx time it happens check the objective and see if it's dewing up and also check that your breath hasn't condensed on the eyepiece.

At this time of year many of us can't see much (!!?) without using dew heaters to keep moisture away.