Two giants of the solar system huddle close together in the evening twilight the next few days. The viewing window is short, so you need to time it just right to see them.

Jupiter and Uranus are low in the west as twilight fades. Jupiter is easy to pick out — it looks like a brilliant star. Uranus is just above it tonight, by about the width of your finger held at arm’s length. But you need binoculars to pick it out. The planets will slide past each other on Sunday night.

Uranus is the Sun’s third-largest planet — four times the diameter of Earth. Its atmosphere is topped by an organic “haze,” which makes it tough to see much below it. The atmosphere consists mainly of hydrogen and helium. These elements are left over from the planet’s formation, from the cloud of gas that enveloped the young Sun.

The third-most-abundant member of the atmosphere is methane. It’s found mostly near the top of the atmosphere. Methane absorbs redder wavelengths of light, so Uranus looks like an almost featureless blue-green ball.

Methane is at least partially responsible for the high-altitude haze. Methane itself makes up part of the haze. The ultraviolet light from the Sun breaks apart some of the methane molecules. Their carbon and hydrogen then combine in different ways to make ethane, acetylene, and other compounds. So the haze is like the smog found over major cities — blocking much of this giant planet from view.

Script by Damond Benningfield