| |
Space Station Info >> Phases Of Venus
Phases Of Venus
Since its orbit takes it between
the Earth and the Sun, as seen from the Earth,
Venus exhibits visible phases as same as Earth’s
moon. Galileo Galilei was the first person to
observe the phases of Venus in December 1610,
an observation which supported Copernicus's then
contentious heliocentric description of the solar
system. He also noted changes in the size of Venus's
visible diameter when it was in different phases,
signifying that it was farther from Earth when
it was full and nearer when it was a crescent.
This inspection strongly supported the heliocentric
model. Venus (and also Mercury) is not visible
from Earth when it is full, since at that time
it is at superior conjunction, rising and settings
are along with with the Sun and so lost in the
Sun's glare.
 |
Venus is brightest when about
25% of its disk is illuminated; this usually
occurs 37 days both before (in the evening
sky) and after (in the morning sky), its
inferior conjunction. Its greatest elongations
happen approximately 70 days before and
after inferior conjunction, at which time
it is half full; between these two intervals
Venus is actually visible in broad daylight,
if the observer knows specifically where
to look for it. The planet's period of retrograde
motion is 20 days on either side of the
inferior conjunction. Indeed, through a
telescope Venus at greatest elongation appears
less than half full due to Schröter's
effect first noticed in 1793 and shown in
1996 as owing to its thick atmosphere. |
Sometimes, Venus can be seen
in both the morning (before sunrise) and evening
(after sunset) on the same day . This circumstances
arises when Venus is at its maximum separation
from the ecliptic and concurrently at inferior
conjunction; then one hemisphere (Northern or
Southern) will be able to see it at both times.
This occasion presented itself most recently for
Northern Hemisphere observers within a few days
on either side of March 29, 2001, and for those
in the Southern Hemisphere, on and around August
19, 1999. These relevant events repeat themselves
every eight years pursuant to the planet's synodic
cycle.
|
|
