Geosystems Chapter 2

Perihelion

Closest position from the Sun Earth is there during the Northern Hemisphere winter on January 3rd.

Sunrise

The moment when the disk of the Sun first appears above the horizon in the east.

Revolution

Earth's orbital revolution around the sun.

Declination

Latitude of the sub solar point

Earth's Orbit

Around the Sun is presently elliptical--a closed, oval path

Speed of Light

300,000 kmps or 186,000 mps Light-year is known as the unit of measurement for the vast Universe.

Axil tilt

A flat surface that intersects Earth's elliptical orbit about the Sun, with half of the Sun and Earth above the plane and half below.

Milky Way Galaxy

A flattened, disk-shaped mass in the form of a barred-spiral--a spiral with a slightly barred or elongated core of stars.

Altitude

Angle between the horizon and the Sun

Daylength

Duration of exposure to insolation. Varies during the year depending on latitude.

Fall Equinox

Earth's orientation is such that the circle of illumination again passes through both poles so that all parts of the globe experience a 12-hour day and a 12-hour night.

Solar wind

Electrically charged particles emitted from the sun that surge outwards in all directions from the Sun's surface.

Aphelion

Farthest position from the Sun. Earth is there during the Northern Hemisphere summer on July 4th.

Axis

Imaginary line extending through the planet from the geographic North Pole to the South Pole

Summer Solstice

June 20 or 21. The sub solar point migrates from the equator to the Tropic of Cancer. Because the circle of illumination now includes the North Polar region, everything north of the Arctic Circle receives 24 hours of daylight.

Spring Equinox

March 20 or 21. The circle of illumination passes through both poles so that all locations on Earth experience a 12-hour night.

Aurora borealis

Northern Lights

Electromagnetic spectrum

Occupies by a portion of solar radiation. The radiant energy travels at the speed of light to earth. The radiant energy is made up of different wave lengths.

Plane of the ecliptic

Plane touching all points of Earth's orbit.

Insolation

Solar radiation that reaches a horizontal plane at Earth. Radiation arriving at Earth's atmosphere and surface.

Aurora australis

Southern Lights

Tropic of Cancer

Sun's declination is at its position farthest north.

Tropic of Capricorn

Sun's declination is at its position farthest south.

Fusion

The Sun's abundant hydrogen atoms are forced together and pairs of hydrogen nuclei are joined.

Solar Constant

The average insolation received at the thermopause when Earth is at its average distance from the Sun

Winter Solstice

The circle of illumination excludes the North Pole but includes the South Pole.

Axial parallelism

The condition of comparing axis in different months and them always appearing parallel to itself

Wavelength

The distance between corresponding points on any two successive waves. Frequency. The Sun's radiated energy is shortwave radiation that peaks in the short visible wavelengths. Earth's radiated energy is long wave radiation concentrated in infrared wavelengths.

Circle of illumination

The dividing line between day and night. At the equator it is evenly divided. Because the day-night dividing circle of illumination intersects the equator.

Sunset

The moment when the Sun totally disappears below the horizon in the west.

Subsolar Point

The only point receiving insolation perpendicular to the surface (from directly overhead).

Thermopause

The region at the top of the atmosphere, approximately 480km above Earth's surface. The outer boundary of Earth's energy system.

Rotation

Turning on its axis. Complex motion that averages slightly less than 24 hours in duration. Determine daylength