Color in the day and night skies

• Optical phenomena in the atmosphere is varied and can be awe inspiring.

• Can range from auroras to halos, sun pillars to green flashes.

Auroras - caused by interaction of the Sun’s particles (solar wind)

and the magnetosphere of Earth.

Color generation in the atmosphere

• Every color of the “white light” from the Sun can be refracted to varying degrees by passing through a prism.

• Natural prisms include raindrops, clouddrops, and ice crystals.

Crepuscular Rays

• Formed by sunlight streaming through a break in the clouds.

• Also called Jacob’s Ladder

Rainbows

• Rainbows form when light is refracted by cloud and raindrops.

• The observer must have their back to the Sun.

• Note the color order - ROYGBIV in the primary, and reversed in the secondary.

• Center of the rainbow’s arc is the anti-solar point.

Halos (not talking about Angels)• Formed by light coming from

the sun (or moon), then being refracted by ice crystals in the upper atmosphere. The main halo is formed on a circle of 22 degrees out, with the sun being at the center of the halo.

Tangent arc - similar to halo; also called circumzenith arcs

• Tangent arcs - appears occasionally at top of 22 degree halo. When ice crystals fall with long axes parallel to ground.

• Upper tangent arc - when sun is on horizon, arc forms above

• Lower tangent arc - when sun is above horizon, the arc may form on lower part of halo

Tangent arcs

Coronas - similar to halos

• Coronas are caused by light from the sun or moon diffracting around objects

• If around the Sun (upper photo), then it is called a Bishop’s Halo and is usually caused by volcanic particles in the air

Glories

• Glories form in a similar manner to rainbows

Sun dogs, or parhelia

• Sun dogs are formed when light refracts on either, or both, sides of the Sun through ice crystals.

• May show weak colors (red would be inner-most.)

Sun pillars• Formed by reflection

of light from a low Sun off of ice crystals

Green Flash(not the comic-book character)

• Seen on upper rim of rising or setting sun (more common). There is so much atmosphere to penetrate when sun is on horizon, sunlight is refracted. Purple, blue bend the most, red the least. Blue light should appear at top of sun, but blue light is scattered selectively, so green light is seen.

Mirages - Fata Morgana

• Fata Morgana Mirage - (Italian for Fairy Morgana) - uniform horizon transformed into walls and columns with spires. Occurs when temperatures increase with height at surface gradually then more rapidly, then gradually again.

• The Legend of Fata Morgana - Morgana was half sister to King Arthur. She had magical powers and could build castles out of the air. Between Sicily and Italy, whole cities sometimes “appear” then disappear moments later