Looking Up: Width & Wisdom

Feb 20, 2017

This week on Looking Up Hal takes us planet hopping. The final destination will be the planet Uranus.

These are among the first clear images, taken from the distance of Earth, to show aurorae on the planet Uranus.
Credit NASA, ESA, and L. Lamy (Observatory of Paris, CNRS, CNES) / nasa.gov

Some things in the southern Colorado sky are very easy to spot – the moon, super-bright Venus and pretty bright Mars. But other things are much harder to spot, especially when city lights make viewing harder. So today I want to tell you about a little trick you can use this week to find one of the more difficult to spot items, the planet Uranus, using the much brighter and easier to spot planet Mars, in the early evening sky. 

But, I should warn you, both planets are fairly low in the western sky shortly after sunset, so you will be able to spot them most easily if you have an unobstructed view to the west, something Pikes Peak makes a bit challenging for some listeners.

Mars, you may recall from earlier shows, is the red planet! Why, because it is rusty! The surface is covered with rusted iron-rich rocks. It’s smaller than the Earth at only about 4200 miles across, compared to Earth’s 8000 mile diameter. While Mars is not as close to Earth as it gets sometimes, it’s still only about 140 million miles away. Because it is so close, relatively speaking, it’s pretty bright. You should look for the red dot in the sky, above and slightly to the left of the much brighter planet Venus.

As I said, Mars isn’t that impressive right now, but it can be used to help you find something few people would be able to find on their own otherwise – the fascinating planet Uranus. Because, over the next few nights, Mars will appear to “back up” in the sky, getting nearer and nearer to Uranus, until on the night of the 25th, the two planets will be less than the width of your pinky finger at arm’s length.

At over 31,000 miles across, Uranus is one of the gas giant planets and it is a beautiful blue-green color. To find Uranus, start at Mars and move slowly up and to the left a bit. Look for a lovely little blue-green dot. Binoculars or a small telescope will let you see Mars and Uranus in the same field of view, and will let you contrast these two wonders of the solar system. So why is the dot of Uranus so much smaller than Mars? Because it’s over 12 times farther away, at a distance of roughly 1.7 billion miles! Light from the Sun reaches Mars in about 16 minutes, but takes nearly 3 hours to reach Uranus. Not bad for the other pale blue dot in the sky.

If you’d like to take a closer look at 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! 

This is Hal Bidlack for the Colorado Springs Astronomical Society, telling you to keep looking up, Southern Colorado!