The Sound of Science

Jasmine: I’m Jasmine.

Chrissy: And l’m Chrissy.

Jasmine: We’re from NIU STEAM and…

Chrissy: This is the Sound of Science on WNIJ. Several weeks ago, when we were experiencing a typical Northern Illinois Winter, we received a few questions about halos that could be seen around the Moon at night and across the horizon when the Sun is low in the sky.

Jasmine: Both situations occur for the same reason – ice crystals that can be found in the atmosphere. The formation of these ice crystals depend on conditions like temperature, humidity, and the presence of clouds.

Chrissy: While in the atmosphere, water has the ability to exist in a super-cooled liquid state where the temperature is below the freezing point of water. When these water droplets come into contact with tiny particles in the air, they freeze into ice crystals. A great source of these tiny particles can be found within cirrus clouds because of the altitude in which they are found. Cirrus clouds are those wispy silky clouds found in the highest parts of the atmosphere where weather occurs.

Jasmine: When the light of the moon or the sun passes through these crystals it can be reflected, refracted or dispersed and, depending on the shape of these crystals, different light patterns can be seen. The most common patterns that are seen are the 22-degree halo and the 46-degree halo. The degree of the halo refers to the radius of the circle of light made when light passes through hexagon shaped ice crystals.

Chrissy: When the Sun is close to the horizon, either during sunrise or sunset, a special phenomenon can occur. Parhelia are one or two bright patches of light that will sit within the solar halo on either side of the Sun. These glowing orbs of light are more commonly known as “sun dogs” because they follow beside the Sun, much like a dog would when walking with a human.

Jasmine: Sun dogs typically occur during sunrise or sunset because the light of the Sun is passing through a greater thickness of the Earth’s atmosphere and therefore has a
greater likelihood of interacting with ice crystals.

Chrissy: You have been listening to the Sound of Science on WNIJ, where you learn something new everyday.