Venus was Huge. Why?

It just occured to me as I was reading the many transit posts. Why was Venus
so apparently huge? It seems like the projected image of Venus was much
larger then Venus ever looks during the evening thru the scope. Why would
that be?

BV.

It just occured to me as I was reading the many transit posts. Why was Venus
so apparently huge? It seems like the projected image of Venus was much
larger then Venus ever looks during the evening thru the scope. Why would
that be?


When venus is between us and the sun it is about as close to us as it can get
and thus as large as it can get. When Venus passed in front of the sun, it was
58 arc-seconds in diameter, almost twice the diameter of Jupiter.

In order for Venus to be fully illuminated, it must be close to opposition
since it is inside of us. As it comes closer, it becomes less fully
illuminated until it nothing but a thin sliver, but that sliver is large in
diameter, the last few days in May it was about 53 arc-seconds.

jon

Benign Vanilla wrote:

It just occured to me as I was reading the many transit posts. Why was Venus
so apparently huge? It seems like the projected image of Venus was much
larger then Venus ever looks during the evening thru the scope. Why would
that be?

For the same reason Mars appears much larger when it is at opposition
every two years; it is at its closest point to the earth. Note that
when Venus is closest to us it must be near the sun. This makes it
difficult to observe, so it is not the typical view at the scope.

Clear skies,
Greg

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To reply have a physician remove your spleen

Could it also be somewhat similar to the "Moon Illusion" where the moon
"appears" to be larger when near the horizon as opposed to when it's
overhead? With Venus, you normally don't see it close to much of anything
else other than other stars. During a transit you have the Sun right there
for a relative comparison.

Also being silhouetted by the Sun and being a dark object seeing against a
brighter object is there some illusion that adds to the fact that Venus is
as close as it get to the Earth, and together this makes Venus appear larger
than expected?

I know in the world of art, that placing a light object against a dark
object or visa versa can make a big difference in the way an observer
perceives a shape.

Just some thoughts,
Francis Marion

"francis marion" wrote in message
news:uomyc.17956$0y.9725@attbi_s03...
Could it also be somewhat similar to the "Moon Illusion" where the moon
"appears" to be larger when near the horizon as opposed to when it's
overhead?

I suspect there is a little of the illusion effect in play along with the
opposition.

Clear Skies

Chuck Taylor
Do you observe the moon?
Try http://groups.yahoo.com/group/lunar-observing/
And the Lunar Picture of the Day http://www.lpod.org/
************************************

Benign Vanilla wrote:

It just occured to me as I was reading the many transit posts. Why was Venus
so apparently huge? It seems like the projected image of Venus was much
larger then Venus ever looks during the evening thru the scope. Why would
that be?

I was surprised at first -- but after thinking about it for a
few seconds, I don't think it was that huge. Did you see any
shots of the Venus occulation a few weeks ago? The relative
size to the Moon was indeed huge. Keep in mind that Venus is
a bit more than three times closer than the Sun.

Also, when looking at Venus (in normal conditions) you don't
see the entire disk -- you see a "Crescent-Moon" shaped arc,
which may give the impression of being smaller.

Carlos
--

Could it also be somewhat similar to the "Moon Illusion" where the moon
"appears" to be larger when near the horizon as opposed to when it's
overhead? With Venus, you normally don't see it close to much of anything
else other than other stars. During a transit you have the Sun right there
for a relative comparison.

As others have mentioned, Venus appears larger because it's at its
closest approach. Amazing shots like the one at
http://antwrp.gsfc.nasa.gov/apod/ima...pHa_vt2004.jpg don't
accurately show how much larger the Sun is than Venus. In actuality,
Venus compared to the Sun is nearly four times smaller in diameter
than the image shows. The silhouette there actually corresponds more
closely to an image of Neptune against the Sun, at the Sun's distance.

Cheers,
Ritesh

In article ,
Jon Isaacs wrote:

When venus is between us and the sun it is about as close to us as it can get
and thus as large as it can get. When Venus passed in front of the sun, it
was 58 arc-seconds in diameter, almost twice the diameter of Jupiter.

OTOH Jupiter is now not that far from minimum apparent size. When near
opposition, Jupiter's apparent diameter is some 45 arcsecond large, i.e. not
that much smaller than Venus during transit.

However, Venus at inferior conjunction does have the largest apparent diameter
of all the planets. Jupiter is second, and Mars at a favourable opposition
is third.

In order for Venus to be fully illuminated, it must be close to opposition
since it is inside of us.

I suppose you mean close to superior conjunction. Since Venus orbits
inside the Earth's orbit, Venus can never reach opposition. It cannot
even reach quadrature, as seen from the Earth.





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