Please click on the photos to enlarge and clarify them.
Have you stopped this week to wonder what those two bright stars are, midway up the northwestern sky at twilight? The brighter and whiter of the two (lower right) is the planet Venus and the bright, yet dimmer, pale white ‘star’ is the planet Jupiter.
Venus (lower right) and Jupiter in the twilight sky, June 24, 2015.
Venus (lower right) and Jupiter in the night sky (10:15pm), June 26, 2015. Note how they’ve closed ranks in just two nights.
Venus (lower right) and Jupiter in the night sky (945pm), June 28, 2015.
Venus (lower left) and Jupiter in planetary conjunction (closest apparent approach to one another) (10:00pm), June 30, 2015.
Venus and Jupiter with a 300x zoom lens (10:00pm), June 30, 2015. Note the faint stars just to the upper left and lower right of dimmer Jupiter. These are two of Jupiter’s many moons.
The previous photo enhanced to make the two ‘Jovian moons’ more visible. The moon to the lower right of Jupiter is a bit more difficult to see — it appears closer to the planet than the moon to the upper left.
Venus and Jupiter have now reached their closest apparent distance to one another (called a planetary conjunction) on June 30.
While Venus clearly dominates Jupiter in the sky, here are a few facts to consider. At magnitude -4.6 (magnitude is a measure of brightness), Venus is now as bright as it can possibly get. It is the third brightest object in the sky, after the sun and the moon. By comparison, Jupiter is currently shining at magnitude -1.8. That’s bright enough to be the fourth brightest object in the sky, but it is 2.5 times dimmer than what Venus currently is.
The diameter of Venus is 7,520 miles (FYI, Earth’s diameter is 7,918 miles, slightly larger than Venus). By contrast, Jupiter, the largest planet in the solar system, is 88,732 miles in diameter – that’s eleven times the diameter of Venus. So, why isn’t Jupiter a lot brighter than Venus right now?
Let’s start by considering how far the two planets are from your eyes. Venus is currently 51 million miles from Earth, while Jupiter is 561 million miles away. So, one reason Jupiter is dimmer than Venus is because it’s eleven times farther away from us.
Let’s also consider their relative distances from the sun, the source of their light. Venus, the second planet from the sun, circles our star at an average distance of 67 million miles. Jupiter, on the other hand, circles the sun at an average distance of 780 million miles, again, about eleven times farther away from the sun than Venus. Since both planets are cloud-covered and shine by reflected sunlight, Venus, being much closer to the sun than Jupiter, receives much more sunlight and appears to be brighter as a result.
So, while Jupiter has a diameter that is eleven times that of Venus, it’s Venus who significantly outshines our largest planet because 1) Venus is eleven times closer to Earth and, hence, to your eyes than Jupiter is, and 2) Venus is eleven times closer to the sun, the source of both planets’ brightness. There are other factors, but these are the biggies.
Take a moment each night to watch the two planets separate over the next week or so. It should be no secret, that Venus appears to be doing the bulk of the moving against the background of the stars because, being closer to the sun than Jupiter, it appears to travel much faster in its orbit. Plus, because Venus is so much closer to you than distant Jupiter is, it seems to move more quickly, in the same way that a car driving down your street appears to move far more quickly than a distant airplane crossing the sky.
But, even without all those facts and figures, you can still enjoy the dazzling spectacle taking place over Oakland, of these two bright planets dancing in our evening sky, as they move past one another during the next few nights. And if you turn off unnecessary lights, you can help put a dent in Oakland’s light pollution and make the night sky more enjoyable for all.
Keeping Oakland Beautiful is everybody’s business.
We encourage you to share your thoughts in the reply section. We welcome the dialogue and learning of others’ perspectives.