Astronomical Transit Article Index for
Astronomical 		Website Links For
Transit 		 

Information About

Astronomical Transit
  CATEGORIES ABOUT ASTRONOMICAL TRANSIT
   
astrometry
   
astronomical transits
   
astronomical events
   
technical factors of astrology
   
astrological aspects
   
SHOPPER'S DELIGHT
 
Shop For:  
Department
Price Minimum:
Price Maximum:
      



The term transit or '''astronomical transit''' has two meanings in astronomy:

  • A transit is the Astronomical event that occurs when one Celestial Body appears to move across the face of another celestial body, as seen by an observer at some particular vantage point.

  • A transit occurs when a celestial body crosses the Meridian due to the Earth's rotation, about halfway between rising and setting. For instance, the Sun transits the meridian at solar Noon . Observation of meridian transits was once very important for timekeeping purposes.


The rest of this article refers to the first kind of transit.


DEFINITION

The word "transit" refers to cases where the nearer object appears considerably smaller in apparent size than the more distant object. Cases where the nearer object appears larger and completely hides the more distant object are known as Occultation s. Cases where one object moves into the shadow of another are known as Eclipse s. Each of these three terms are the visible effects of a Syzygy .

One example of a transit involves the motion of a Planet between a Terrestrial observer and the Sun . This can happen only with Inferior Planets , namely Mercury and Venus (see Transit Of Mercury and Transit Of Venus ). However, as seen from outer planets such as Mars , the Earth Itself Transits The Sun on occasion.

transits across Jupiter as seen by Cassini spacecraft]]
transits Titan , as seen by the Cassini probe; in the background, little Prometheus is Occulted by the Rings Of Saturn ]]

The term can also be used to describe the motion of a Satellite across its parent planet, for instance one of the Galilean satellites ( Io , Europa , Ganymede , Callisto ) across Jupiter , as seen from Earth .

A transit requires three bodies to be lined up in a single line. More rare are cases where four bodies are lined up. One such case occurred on , and Mercury and Venus both simultaneously transited the Sun as seen from Saturn (see Transit Of Mercury From Saturn and Transit Of Venus From Saturn ).

In recent years the discovery of Extrasolar Planet s has excited interest in the possibility of detecting their transits across their own Stellar primaries. HD 209458b is the first such transiting planet to be discovered.


MUTUAL PLANETARY TRANSITS AND OCCULTATIONS

In rare cases, one planet can transit in front of another. The next time this will happen (as seen from Earth) will be on will cause actual observed times to vary by a few minutes, depending on the precise location of the observer.

There are only 18 mutual planetary transits and occultations as seen from Earth between 1700 and 2200. Note the long break of events between 1818 and 2065.

transiting Jupiter , as it did on January 3, 1818.]]





CONTACTS

During a transit there are four "contacts", when the Circumference of the small circle (small body disk) touches the circumference of the large circle (large body disk) at a single point. The contacts happen in the following order:
  • First contact: the smaller body is entirely outside the larger body, moving inward

  • Second contact: the smaller body is entirely inside the larger body, moving further inward

  • Third contact: the smaller body is entirely inside the larger body, moving outward

  • Fourth contact: the smaller body is entirely outside the larger body, moving outward



TRANSIT VISIBILITY TABLE



SEE ALSO



For transit of planets in front of others, see also Occultation .


EXTERNAL REFERENCES


  • Meeus, Jean: ''Transits.'' Richmond, Virginia: Willmann-Bell, Inc., 1989, ISBN 0-943396-25-5.

  • Meeus, Jean: ''Astronomical Tables of the Sun, Moon and Planets.'' Richmond, Virginia: Willmann-Bell, Inc., 1995, ISBN 0-943396-45-X.