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Venus at its brightest this Sunday morning |
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April 29, 2017 |
By Bruce McClure
EarthSky.org
Before sunrise tomorrow – April 30, 2017 – the
planet Venus will display its greatest
illuminated extent. That means the planet’s
daytime side is now covering more square area of
Earth’s sky than at any other time during its
present morning apparition. So this weekend is a
great time to look for Venus!
It will be shining at or near its greatest
brilliancy before sunrise. Especially if you see
it with the eye alone, its brightness will amaze
you.
Around times of greatest brilliancy for Venus,
many will report it as a UFO.
You might think Venus appears most brilliant
when we see its disk as most fully illuminated
from Earth. Not so.
If you were to observe Venus with the telescope
at its greatest illuminated extent, you’d see
that Venus’s disk is only a touch more than
one-quarter illuminated by sunshine.
A full Venus is always on the far side of the
sun from us, so its disk size at full phase
always appears small to us on Earth.
It’s only when we see Venus as a crescent – when
Earth and Venus are on the same side of the sun,
with Venus preparing to pass between us and the
sun, or just having so passed – that this world
is close enough to us to exhibit its greatest
illuminated extent.
At these special times, the daytime side of
Venus covers the greatest area of Earth’s sky.
Venus passed between the Earth and sun on March
25, 2017 and so entered Earth’s morning sky.
Venus will shine in our sky at dawn for the rest
of 2017 and finally transition back to the
evening sky on January 9, 2018.
This chart gives you a bird’s-eye view of Earth
and Venus in orbit, helping you see how and why
Venus can transition from evening to morning
sky.
Because Venus orbits the sun inside Earth’s
orbit, we can’t see Venus opposite the sun in
our sky (like the full moon).
We can’t even see Venus 90-degrees from the sun
(like the half-lit quarter moon).
At most, Venus strays no farther than 47-degrees
from the sun in our sky.
This is called Venus’ greatest eastern
elongation when Venus appears in the evening sky
and greatest western elongation when Venus is in
the morning sky.
Venus reaches its greatest elongation in the
evening sky about 72 days before inferior
conjunction, and then reaches its greatest
elongation in the morning sky some 72 days after
inferior conjunction. If you look at Venus
through a telescope at these times, you’ll see
that its disk is about 50-percent illuminated by
sunshine.
Venus exhibits its greatest illuminated extent
about 36 days before – and after – inferior
conjunction. Through the telescope, Venus
appears about 25-percent illuminated in sunshine
at these times. 36 days before inferior
conjunction, it’s Venus’ brightest appearance in
the evening sky; 36 days after inferior
conjunction, it’s Venus brightest appearance in
the morning sky.
Even though this world is only about one-quarter
illuminated in sunshine right around April 30 as
seen from Earth, Venus is nonetheless shining at
its brightest best in the morning sky! |
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