Earth phenomena

An aurora ( aurorae or auroras) is a natural light display in Earth’s upper atmosphere caused by charged particles from the Sun colliding with atoms in the atmosphere. These collisions excite oxygen and nitrogen, which then emit light of different colors such as green, red, and purple. When observed in high-latitude regions they are called polar lights and aurora polaris. In the Arctic they are called northern lights (aurora borealis); in the Antarctic, the terms southern lights (aurora australis) are used. Auroras display dynamic patterns of radiant light that appear as curtains, rays, spiral

thumb|Sunrise seen over the Atlantic Ocean through [[cirrus clouds on the Jersey Shore at Spring Lake, New Jersey, U.S.]] Sunrise (or sunup) is the moment when the upper rim of the Sun appears on the horizon in the morning, at the start of the Sun path. The term can also refer to the entire process of the solar disk crossing the horizon.

thumb|upright=1.35|Actual sunset: Two minutes before the Sun disappears below the horizon.

thumb|Totality during the solar eclipse of August 11, 1999, showing the [[solar corona and prominences]] thumb|The lunar umbra on Earth during the solar eclipse of August 21, 2017, as seen from space

thumb|Twilight is the period between dawn and [[sunrise, and between sunset and dusk.]] thumb|Morning twilight: astronomical, nautical, and civil stages at dawn. The apparent disk of the Sun is shown to scale. thumb|Evening twilight: civil, nautical, and astronomical stages at dusk. The solar disk is shown to scale.

thumb|right|Late summer dawn over the Mojave Desert, [[California]] thumb|Dawn is sometimes considered the beginning of morning twilight, the period of twilight, or the time of sunrise. Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the appearance of indirect sunlight being scattered in Earth's atmosphere, when the centre of the Sun's disc has reached 18° below the observer's horizon. This morning twilight period will last until sunrise (when the Sun's upper limb breaks the horizon), when direct sunlight outshines the diffused light.

natural phenomenon when daylight lasts for more than 24 hours, occuring only inside or close to the polar circles

natural phenomenon when the night lasts for more than 24 hours, occuring only inside the polar circles

ice formed from frozen seawater

flow of excess rainwater not infiltrating in the ground over its surface

moving line that separates the illuminated day side and the dark night side of a planetary body

period of twilight in the morning or evening

first and last hour of sunlight during the day

thumb|right|upright=1.35|Landers, California at nautical dusk (20-second exposure)

type of rainbow formed by airborne water droplets

apparent solar time minus mean solar time

thumb|Coastal polynyas are produced in the Antarctic by katabatic winds thumb|Katabatic wind spilling off an ice shelf|upright thumb|A frosty Arctic condensation plume marks this polynya near the west shore of Hudson Bay. This one (and others nearby) are likely kept open by tidal currents. Mile-high west-facing aerial view.

pinkish glow seen before sunrise or after sunset extending roughly 10–20° above the horizon

sea ice cover of the Arctic Ocean and its vicinity

thumb|right|The night side of the Moon, illuminated by earthshine, becomes visible next to the narrow crescent (11 percent, age of the Moon = 3.3 days) with ash-grey moonlight.

thumb|A STEVE over Little Bow Resort, [[Alberta, in August 2015]] thumb|A STEVE over Crossfield, Alberta, in March 2018 (around 12:30 a.m.)

ice crystals that form in supercooled water that is too turbulent to permit coagulation into sheet ice

shower of particles from a high energy cosmic ray hitting Earth's atmosphere

form of ice

pool of open water that forms on sea ice in the warmer months of spring and summer

natural phenomenon

process by which salts are expelled from freezing water

visual perception of the sky and how it scatters and diffuses light.