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Ch. 2 - Geography 102

"Solar Energy to Earth and the Seasons"


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Point at which earth is farthest from the sun, July 4th.
subsolar point
The only point receiving perpendicular insolation at a given moment- the sun directly overhead.
solar constant
The amount of insolation intercepted by earth on a surface perpendicular to the sun's rays when earth is at its average distance from the sun.
speed of light
Specifically 299, 792 kilometers per second, or more than 9.4 trillion kms per year ( a distance known as a light year)
axial parallelism
Earth's axis remains the same throughout the year; north pole always points towards north star because of this.
Glowing light displayed in the ionosphere, stimulated by the interaction of solar wind with oxygen and nitrogen gases and atoms at high latitudes.
planetesimal hypothesis
Proposes a process by which early proto-planets formed from condensing masses of a nebular cloud of dust, gas and icy comets; a formation process now being observed in other parts of the galaxy.
Solar radiation that is incoming to Earth systems
Top of atmosphere, used in determination of solar constant.
The process of forcibly joining positively charged hydrogen and helium nuclei under extreme pressure and temperature; occurs naturally in thermonuclear reactions within stars, such as our sun.
plane of the ecliptic
A plane (flat surface) intersecting all the points of earth's orbit.
autumnal equinox
September- Sun's declination is at equator...equal amounts day and night
The latitude that receives direct overhead (perpendicular) insolation on a particular day; the subsolar point point migrates annually through 47 degrees of latitude between the Tropics of Canacer and Capricorn.
Turning of earth on its axis; averaging about 24 hours in duration; determines day-night relation; counterclockwise when viewed from above the north pole and from above the equator, west to east or eastward.
axial tilt
Earth's axis tilts 23.5 degrees from a perpendicular to the plane of the ecliptic.
The imaginary line going through the poles around which the earth rotates.
electromagnetic spectrum
All the radiant energy produced by the sun placed in an ordered range, divided according to wavelengths.
Milky Way Galaxy
A flattened, disk-shaped mass in space estimated to contain up to 400 billion stars (including our solar system)
The angular distance between the horizon (a horizontal plane) and the sun (any point in the sky)
The mutal force exerted by masses of objects that are attracted to one another and produces in an amount proportional to each object's mass.
The moment when the disk of the sun totally disappears.
The annual orbital movement of the earth around the sun; determines length of year and seasons
Magnetic disturbances on surface of the sun, occurring in an average 11-year cycle; related flares, prominences, and outbreaks produce surges in solar wind.
Earth's magnetic field force, which is generated by dynamo-like motions within the planet's outer core; deflects the solar wind flow toward the upper atmosphere above each pole.
summer solstice
June- Sun's declination is at Tropic of Cancer (opposite of winter solstice)
A measurement of a wave; the distance between the crests of successive waves. The number of waves passing a fixed point in 1 second is called the frequency of a ________
Duration of exposure to insolation, varying during the year depending on latitude; an important aspect of seasonality.
solar wind
Clouds of ionized (charged) gases emitted by the sun and traveling in all directions from the sun's surface. Effects on earth include auroras, disturbance of radio signals, and possible influences on weather.
Point at which earth is closest to the sun, January 3rd.
vernal equinox
March - Sun's declination is at equator...we experience equal amounts of day and night. Sun rises at north pole and sets at south pole.
The moment when the disk of the sun first appears over the horizon.
circle of illumination
The division between light and dark on earth; a day-night great circle
winter solstice
December - Sun's declination is at the Tropic of Capricorn, 23 degrees in latitude. Antarctic circle = 24 hour day, Arctic = 24 hour night

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