posted on Aug, 21 2011 @ 07:54 AM
Originally posted by ticklemytweeder
reply to post by lkpuede
Yeah, but the pic posted on pg. 3 Of this thread shows Mercury high in the sky w/ Venus and Jupiter. Mercury could only be in that position during
daylight hours. So, yes, I did seriously ask that question. I don't doubt you can see Mercury at sunrise and sunset.. When the Sun is at a low angle
at either dusk or dawn it's quite pragmatic for viewing something orbiting close to the sun. Soon after, the sky goes blue due to the angle of the
daytime sun and Mercury is unseen by the naked eye.
When you said "...the pic ... shows Mercury high in the sky..." you made a common assumption that the photograph's field-of-view was comparable to
what we see with our naked eye. It's not.
Link to the photo
Were this photo taken with a standard point & shoot with no magnification, the planetary grouping would be a small feature in the middle of a much
larger scene (if it showed-up at all, because the exposure with such a camera is usually too short to see planets or stars). This photographer may
have used a telephoto lense and definitely used an exposure longer than 1-second because several stars are visible He also cropped the resulting
image for good artistic composition.
, I found that the angular separation between Venus & Mars at that time (May 13, 2011) was ~5
degrees. Using this as a ruler, we can see that the field-of-view is about 10 degrees wide and 15 degrees tall. Mercury, in the image, is roughly 13
degrees above the horizon. I was able to confirm that the photo was taken at around 6:30 local time which for its southern latitude was slightly more
than an hour before sunrise. Note that the long exposure also makes the sky appear brighter than it looked to the eye. He probably didn't have much
more than "the first rosey fingers of dawn."
Using JPL's Solar System Simulator
, I made a map of the planetary positions at that time:
Jupiter is about a foot above your monitor, in line with the other planets.
As you can see, the angle between the Sun and Mercury as seen from Earth is 20-25 degrees. The Earth rotates 15 degrees per hour. Depending on your
latitude (and the mid-southern hemisphere was optimum for this conjunction) this was ample separation to see that planet well before dawn.
on 21-8-2011 by Saint Exupery because: I remeasured an angle for accuracy.