FACTOID # 23: Wisconsin has more metal fabricators per capita than any other state.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
   
 
WHAT'S NEW
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Diurnal motion

Diurnal motion is an astronomical term referring to the apparent daily motion of stars in "orbit" around the Earth, caused by the Earth's rotation around its axis. It is a rotation around the axis between the two celestial poles.


It takes Earth 23 hours, 56 minutes and 4.09 seconds (1 sidereal day) to rotate around the axis connecting the North Pole and the South Pole.


Direction of the motion on the Northern hemisphere:

  • looking to the north, below the North Star: left-right, west-east
  • looking to the north, above the North Star: right-left, east-west
  • looking to the south: left-right, east-west

Thus northern circumpolar stars move anti-clockwise around the North Star.


At the North Pole, north, east and west are not applicable, the motion is simply left-right, or looking vertically upward, anti-clockwise around the zenith.


For the southern hemispere, interchange north/south and left/right, and replace North Star by southern celestial pole. The circumpolar stars move clockwise around it. East/west are not interchanged.


At the equator both celestial poles are at the horizon and motion is anti-clockwise (i.e. to the left) around the North Star and clockwise (i.e to the right) around the southern celestial pole. All motion is from east to west, except for the two stationary points.


The daily path of an object on the celestial sphere, including the possible part below the horizon, has a length proportional to the cosine of the declination. Thus the speed of the diurnal motion of a celestial object is this cosine times 15 /hr = 15'/min = 15"/sec, i.e. (compare angular diameter):

  • up to a Sun or Moon diameter every two minutes
  • ca. four seconds for the largest planet
  • 2000 diameters of the largest stars per second

Diurnal motion can be seen in time-exposure photography [1] (http://www.nao.ac.jp/pio/Conste/diu_nso1.jpg). Circumpolar stars close to the celestial pole move only slowly. Conversely, following the diurnal motion with the camera, to eliminate it on the photograph, can best be done with an equatorial mount, which requires adjusting the right ascension only; a telescope may have a motor to do that automatically (sidereal drive).


See also: celestial sphere, positional astronomy.


  Results from FactBites:
 
Diurnal motion - Wikipedia, the free encyclopedia (342 words)
Diurnal motion is an astronomical term referring to the apparent daily motion of stars in "orbit" around the Earth, caused by the Earth's rotation around its axis.
At the equator both celestial poles are at the horizon and motion is anti-clockwise (i.e.
Conversely, following the diurnal motion with the camera, to eliminate it on the photograph, can best be done with an equatorial mount, which requires adjusting the right ascension only; a telescope may have a motor to do that automatically (sidereal drive).
Prograde and retrograde motion - Wikipedia, the free encyclopedia (799 words)
Retrograde motion is the orbital motion of a body in a direction opposite that which is normal to spatial bodies within a given system.
The apparent motion of most bodies in the sky is from east to west.
However it is possible to observe a body moving west to east, such as an artificial satellite or Space Shuttle that is orbiting eastward (the preferred direction, because the rotation of the Earth assists in acquiring the required orbital speed).
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m