Courtesy of EarthSky
A Clear Voice for Science
www.EarthSky.org

Mars is near the waning gibbous moon on the evening of January 2.

Two major astronomical events are taking place today. First, our planet Earth is at perihelion – its closest point to the sun for the year. Second, tonight’s waning gibbous moon pairs up with a brilliant planet – the world next door – Mars. You can see Mars and the moon tonight from mid-evening until dawn.

First, Earth’s perihelion – our closest point to the sun – today. It happens every year at this time, despite the fact that January is a winter month for the northern hemisphere. We’re farthest away from the sun in early July, during our northern summer. So you can see that Earth’s distance from the sun isn’t what causes the seasons.

Earth is about 5 million kilometers – or 3 million miles – closer to the sun today than it will be in early July. That’s not a huge change – so, on Earth, it’s mostly the tilt of our world’s axis that creates winter and summer. In winter, your part of Earth is tilted away from the sun – in summer, it’s tilted toward the sun.

Now back to Mars – the world near the moon tonight. Mars also tilts on its axis. And this axial tilt creates the martian seasons, just as on Earth. But Mars orbit is more elliptical than Earth’s, so Mars’ distance from the sun varies more, and that variation does affect martian surface temperatures.

So you have two worlds to think about today. Earth closest to the sun and Mars near the waning gibbous moon from mid-evening until dawn. After rising, the shining couple will glorify the nighttime until morning dawn. The moon and Mars will be in each other’s vicinity on the sky’s dome for these next two nights.

Written by Bruce McClure, Deborah Byrd