Ann wrote:
I was surprised to see that the surface brightness of the Moon appears to be higher than the surface brightness of Jupiter. Given the fact that the Moon is very dark, about as dark as asphalt, I would have expected the surface brightness of Jupiter to be higher. Does anyone know an explanation for this?
This is just a guess -- the Moon is closer to the Sun and closer to the Earth, so she gets more light from the Sun than Jupiter does, and more of the Moon's light gets to Earth than light from Jupiter. If somebody more mathematically competent than I am would calculate the surface areas of the the relevant spheres I would be tickled pink.
Assuming that Jupiter is actually resolved in the photo (more or less)
the two important factors are relative albedos & distances from the Sun.
Jupiter's albedo is 0.52 vs. the Moon's albedo of 0.136
so Jupiter should be 3.82 times brighter (a la Ann).
However, Jupiter is 5.2 times further from the Sun making it 27 times dimmer.
neufer wrote:Assuming that Jupiter is actually resolved in the photo (more or less)
the two important factors are relative albedos & distances from the Sun.
Jupiter's albedo is 0.52 vs. the Moon's albedo of 0.136
so Jupiter should be 3.82 times brighter (a la Ann).
However, Jupiter is 5.2 times further from the Sun making it 27 times dimmer.
Hence: Jupiter is about 7 times dimmer.
Ah, math. Thanks! But doesn't the distance from the object to the observer make a difference too? If two stars are equally bright, but one star is twice as far away as the other star, then the closer star will appear four times brighter than the farther star. (I can do that much math.) Wouldn't the same hold true for objects in the solar system?
neufer wrote:Assuming that Jupiter is actually resolved in the photo (more or less)
the two important factors are relative albedos & distances from the Sun.
Jupiter's albedo is 0.52 vs. the Moon's albedo of 0.136
so Jupiter should be 3.82 times brighter (a la Ann).
However, Jupiter is 5.2 times further from the Sun making it 27 times dimmer.
Hence: Jupiter is about 7 times dimmer.
Ah, math. Thanks! But doesn't the distance from the object to the observer make a difference too? If two stars are equally bright, but one star is twice as far away as the other star, then the closer star will appear four times brighter than the farther star. (I can do that much math.) Wouldn't the same hold true for objects in the solar system?
But the stars are NOT resolvable.
I'm assuming that Jupiter is basically resolved in the picture and that the issue
brought up by Ann involves brightness per pixel (not brightness times # of pixels).
rstevenson wrote:
Okay, I'm confused. I had a look tonight, with a rare clear sky to help. Jupiter was not at all in that position. It was to the left of the Moon by almost two full Moon widths. So was the caption under the picture wrong? Did they mean Christmas Eve perhaps?
At your location, shortly after moonrise, Jupiter was above and to the left of the Moon (in the east). Over the next few hours, it shifted to the right. For observers at middle and high northern latitudes, the closest the two bodies got was about a degree- two lunar widths.
Amazing Video of a Lunar Occultation
by Jason Major on December 28, 2012
<<Captured on camera by astrophotographer Rafael Defavari from his location in São Bernardo do Campo, Brazil, this video shows the Moon passing in front of Jupiter during an occultation event on December 25, 2012. Nice work!
The Moon blocked the view of the giant planet for a full hour and ten minutes. The video plays at 5x actual speed.
‘Tis the season for lunar occultations, too… the last one occurred on November 28, and the next will be on January 22, 2013.>>
neufer wrote:Assuming that Jupiter is actually resolved in the photo (more or less)
the two important factors are relative albedos & distances from the Sun.
Jupiter's albedo is 0.52 vs. the Moon's albedo of 0.136
so Jupiter should be 3.82 times brighter (a la Ann).
However, Jupiter is 5.2 times further from the Sun making it 27 times dimmer.
Hence: Jupiter is about 7 times dimmer.
Ah, math. Thanks! But doesn't the distance from the object to the observer make a difference too? If two stars are equally bright, but one star is twice as far away as the other star, then the closer star will appear four times brighter than the farther star. (I can do that much math.) Wouldn't the same hold true for objects in the solar system?
But the stars are NOT resolvable.
I'm assuming that Jupiter is basically resolved in the picture and that the issue
brought up by Ann involves brightness per pixel (not brightness times # of pixels).
Thanks for the clarification. To a naked eye observer, unlike somebody looking at a picture on a computer screen, the distance from the observer to the object does affect perceived brightness, and, everything else being equal, brightness will be the inverse square of distance. The Moon is the brightest object in our sky mostly because she is so close to Earth.
Also, thanks for Rafael Defavari's awesome video of the occultation! You can see irregularities on the Moon's dark limb as Jupiter is occulted, and then you can see Io's shadow transiting Jupiter as Jupiter emerges from behind the Moon's bright limb! I love our solar system!
