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Circumpolar star trails in a long-exposure photo of several hours. The stars near the celestial pole leave shorter trails with the long exposure. A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets below the horizon due to its apparent proximity to one of the celestial poles.
Celestial mechanics is the branch of astronomy that deals with the motions of objects in outer space. Historically, celestial mechanics applies principles of physics ( classical mechanics ) to astronomical objects, such as stars and planets , to produce ephemeris data.
A meridian on the celestial sphere matches an hour circle at any time. The hour circle is a subtype whereby it is expressed in hours as opposed to degrees, radians , or other units of angle. The hour circles make for easy prediction of the angle (and time due to Earth's fairly regular rotation , approximately equal to the time) between the ...
In astrophysics, the thermal time scale or Kelvin–Helmholtz time scale is the approximate time it takes for a star to radiate away its total kinetic energy content at its current luminosity rate. [1]
The north and south celestial poles appear permanently directly overhead to observers at Earth's North Pole and South Pole, respectively. As Earth spins on its axis, the two celestial poles remain fixed in the sky, and all other celestial points appear to rotate around them, completing one circuit per day (strictly, per sidereal day ).
The sidereal year differs from the solar year, "the period of time required for the ecliptic longitude of the Sun to increase 360 degrees", [2] due to the precession of the equinoxes. The sidereal year is 20 min 24.5 s longer than the mean tropical year at J2000.0 (365.242 190 402 ephemeris days) .
A-type star In the Harvard spectral classification system, a class of main-sequence star having spectra dominated by Balmer absorption lines of hydrogen. Stars of spectral class A are typically blue-white or white in color, measure between 1.4 and 2.1 times the mass of the Sun, and have surface temperatures of 7,600–10,000 kelvin.
Afternoon analemma photo taken in 1998–99 in Murray Hill, New Jersey, U.S., by Jack Fishburn.The Bell Laboratories building is in the foreground. In astronomy, an analemma (/ ˌ æ n ə ˈ l ɛ m ə /; from Ancient Greek ἀνάλημμα (analēmma) 'support') [a] is a diagram showing the position of the Sun in the sky as seen from a fixed location on Earth at the same mean solar time over ...