The two brightest planets in the sky right now—and the two brightest planets, period—are Venus and Jupiter. Shortly after sunset at the end of April, Venus is the very bright object in the west, and Jupiter is only a little less bright high in the southern sky. In actual fact, they never get very close to each other. Venus orbits closer to the sun than does Earth, and Jupiter much farther from it. At their closest, Venus and Jupiter are well over 400 million miles apart: four and a half times the distance between the Earth and the sun.
But if astronomy teaches us anything, it is that what you see very much depends on where you stand. From our vantage point on Earth, Venus and Jupiter sometimes appear to be quite close to each other. And at the end of June, they will be less than half a degree apart, less than the width of a full moon. Such an apparent meeting of two celestial bodies is called a conjunction. Here is a view of the sky at 9 pm tonight (April 24, 2015) as seen from Lynchburg, Virginia.
When we look at the sky, it’s easy to see how our ancestors imagined it as a bowl, with all the celestial objects about the same distance away from us. In fact, it has enormous depth, with some objects like the moon quite close, and others like Jupiter much farther away. Its three-dimensional nature is not readily apparent.
If we take a different perspective—if we stand in a different place—we can see how two objects that appear to be close together do so only because they lie along the same line of sight. Here is a view from above the solar system. In this view, the Earth’s north pole is directly below us, and all the planets orbit the sun in a counter-clockwise direction.
At the end of April 2015, Venus and Jupiter lie in different directions as viewed from the Earth. But as the planets orbit the sun, those nearer the sun move faster. Venus closes on the Earth as the weeks pass, and at the end of June it is much nearer to us. The more distant Jupiter meanwhile has moved only a little along its nearly twelve year long path.
The weeks leading to that night will be rewarding as well, as we watch the two brightest natural sky objects after the sun and the moon approach each other in a cosmic dance, and as we remind ourselves that a different location in the solar system would provide a very different view.