07-01-2015, 03:46 PM
Rainyjim,
I think ericlp was just pointing out Jupiter has a massive gravitational pull, which it does, rather than claiming that it has an effect on how bright it appears. In fact, Jupiter is massive enough that due to gravitational contraction it actually emits more energy than it receives. However, that energy is emitted as infrared light so makes no difference to how bright it appears to our eyes.
On the other hand, that mass has had a big impact on our solar system. For decades many felt that Jupiter helped protect us from incoming asteroids and comets by deflecting their orbits. It turns out that when it comes to asteroids and short-period comets, it actually increases the danger by sending these objects into the inner solar system. However, for the most dangerous objects, long period comets coming from the Oort cloud, it does add some protection by deflecting some of those objects out of the solar system entirely.
Venus is currently much brighter (it isn't always brighter than Jupiter although generally it is). It's much closer than Jupiter but its atmosphere contains highly reflective sulfuric acid clouds which reflect most of the light it receives back into space. In fact, if you have a pair of binoculars and can keep them steady enough, you might be able to see Venus currently appears crescent-shaped, from our perspective more than half its planetary disk is in shadow yet it still appears very bright.
And yes, the two planets are about half a billion miles apart.
I think ericlp was just pointing out Jupiter has a massive gravitational pull, which it does, rather than claiming that it has an effect on how bright it appears. In fact, Jupiter is massive enough that due to gravitational contraction it actually emits more energy than it receives. However, that energy is emitted as infrared light so makes no difference to how bright it appears to our eyes.
On the other hand, that mass has had a big impact on our solar system. For decades many felt that Jupiter helped protect us from incoming asteroids and comets by deflecting their orbits. It turns out that when it comes to asteroids and short-period comets, it actually increases the danger by sending these objects into the inner solar system. However, for the most dangerous objects, long period comets coming from the Oort cloud, it does add some protection by deflecting some of those objects out of the solar system entirely.
Venus is currently much brighter (it isn't always brighter than Jupiter although generally it is). It's much closer than Jupiter but its atmosphere contains highly reflective sulfuric acid clouds which reflect most of the light it receives back into space. In fact, if you have a pair of binoculars and can keep them steady enough, you might be able to see Venus currently appears crescent-shaped, from our perspective more than half its planetary disk is in shadow yet it still appears very bright.
And yes, the two planets are about half a billion miles apart.