The “halo” around the sun and/or moon is produced by high, thin cirrus clouds. Cirrus clouds are ice clouds rather than liquid water droplets that make up most other cloud types.
Cirrus clouds often appear before the onset of warm weather, however they are themselves the coldest of clouds. Because they often rise to heights of 40,000 feet, the moisture contained in them is frozen into ice crystals.
During the day, these cirrus clouds are sometimes difficult to see, but often result in “filtered” sunshine and may give the sky a slightly pale appearance as opposed to a clear-blue cloud-free sky. At night, these thin cirrus clouds are often virtually invisible: stars shine through and the sky appears totally clear.
The ice crystals that make up the cirrus cloud deck act like tiny reflectors at a precise angle from the sun/moon. The angle, or size, of the halo (usually about a 22 degree angle from the centerpoint of the moon/sun) is a function of the “shape” of the ice crystals. There are at times double halos — two circles indicating two different shapes of ice crystals in the cirrus clouds.
Haze (also known as mist) is reduced visibility in the air as a result of abundant water vapor, dust, smoke, etc. near or in contact with the Earth. Although it is invisible to the naked eye, the particles reduce visibility by being sufficiently numerous to give the air an opalescent (unclear) appearance.
Note: We currently have hazy conditions in the local region, due to a layer of Saharan dust.