Looking Up: You Can Call Me Albedo
This week on Looking Up Hal gives us a good reason to get out of bed early on these cold autumn mornings.
Today’s edition of Looking Up is for those folks who are up and at them before dawn. The rest of you can take a break, or you can get up early one day to see an early morning celestial show with the two brightest planets in our Colorado sky, Jupiter and Venus.
For the next few weeks, as you look east before Sunrise, you will likely notice two very bright lights in the pre-dawn sky. The brightest of them is the very beautiful Venus, whose bright white clouds are brilliantly illuminated by the Sun.
Above and to the right of Venus is the dazzling planet Jupiter. Jupiter is the big bad planet of the solar system, with twice the mass of all the other planets put together. Venus is much smaller, a tad smaller than our own Earth. So why is Venus brighter than the much larger Jupiter?
Mostly because of the albedo of the two planets, and even more importantly, the distance they are from Earth. Albedo is a measure of how much of the light that strikes a planet is reflected off into space. In Venus’s case, about 70% of the light that hits it is reflected off, making Venus very reflective and very bright. Jupiter reflects about 52% of its light, so it’s dimmer in that regard. But what really makes the difference is that Venus is 15 times closer to us than Jupiter is. Closeness really matters. For example, the Moon only reflects 12% of the light that hits it, but it is so bright because it is so close.
So take a look at the morning sky and marvel at the brilliant planets and enjoy the celestial show.
If you’d like to take a closer look at Venus and Jupiter or any of the wonderful and amazing things in the sky, please visit csastro.org for a link to information on our monthly meetings and our free public star parties.