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The Synodic Period of Venus
A sky object's synodic period is the time between repeated
appearances of that object, as seen from the Earth, in the same position
with respect to the Sun. Venus' synodic period takes about 584 days
(actually 583.92 days). The following table shows each phase, beginning
with a re-appearance of Venus as the morning star, a heliacal
rising, after a period of being aligned with the Sun and therefore
lost in solar glare.
The first column is the orbital view, which shows the orbits of the
Earth and Venus and the position of the two planets at that point in the
cycle, as seen from north of the Earth's orbit. The second column is the
horizon view, which shows what an observer on Earth would see either
just before sunrise in the east, or just after sunset in the west. The
third column gives the day number and comments about this phase of the
synodic period. The day number for each phase (except the first and
last) are approximate; the middle phases can occur one or two days
earlier or later.
In the orbital view, the blue dot marks the position of the Earth, the
white dot marks the postition of Venus, the yellow ball is the Sun, and
the circles represent the orbital paths of the planets. The planets
orbit the Sun in a counter-clockwise direction as shown by the arrow in
the bottom right corner of each image. The green part of the orbit
circle shows the movement of the planet from the previous to the current
phase of the synodic period.
In the horizon view, the black bar represents the horizon, the yellow
glow represents the sunrise or sunset, and the white dot marks the
position of Venus in the sky. The view shown is either the eastern
(morning) sky at sunrise or the western (evening) sky at sunset. It
assumes ideal observing conditions: a flat, unobstructed horizon, a
cloudless sky and dry air.
Aspects of the Synodic Period of Venus
Venus has moved just far enough ahead of the Earth in its orbit so that
it re-appears in the morning sky and begins a new synodic period. At
this point, Venus is about 10 degrees from the Sun and could be seen by
careful observation just before the Sun rises in the east. Venus then
rises earlier and earlier each day, getting further and further ahead of
the Sun, and higher and higher in the sky at sunrise, until ...
Venus is about 46 degrees ahead of the Sun in the morning sky. Now it
begins to rise later each day, moving back toward the Sun's glare at
sunrise until ...
Venus makes its last appearance as the morning star. Now it begins to
move behind the Sun as seen from the Earth, and so becomes hidden from
Venus is behind the Sun and cannot be seen from the Earth. This point is
called superior conjunction.
Venus has moved far enough away from the Sun to be seen again, this time
as the evening star. At this point, Venus is about 10 degrees from the
Sun and could be seen by careful observation just after the Sun sets in
the west. Venus then sets later and later each day, getting further and
further behind the Sun, and higher and higher in the sky at sunset,
Venus is about 46 degrees behind the Sun in the evening sky. Now it
begins to set earlier each day, moving back toward the Sun's glare at
sunset until ...
Venus makes its last appearance as the evening star. Now it begins to
move in front of the Sun as seen from the Earth, and so becomes hidden
Venus is in front of the Sun and cannot be seen from the Earth. This
point is called inferior conjunction.
Venus re-appears in the morning sky, ending the previous synodic period
and beginning the next. But note that the Earth has moved through one
full orbit (one year or about 365 days) and three-fifths of another
(about 219 days). In that same time, Venus has moved through two of its
own orbits and three-fifths of another.