There are only five dwarf planets: Ceres, Pluto, Eris, Makemake and Haumea. Of these, only one is visible in anything other than a chunky telescope — Ceres. And you can see it this month in nothing more than a pair of binoculars. I stood in the driveway two nights under under a smoky sky and spotted it in my 8x40s near the head of the scorpion. You can, too.
Ceres was the first asteroid discovered, way back in 1801, and the largest object in the main asteroid belt between Mars and Jupiter. Astronomers reclassified it as a dwarf planet in 2006 along with Pluto and three other large but remote asteroids in the Kuiper Belt beyond Neptune. Dwarf planets lie somewhere between asteroids and planets. They’re big enough for self-gravity to have compressed them into spheres, and they orbit the sun (and not other planets) but lack the gravitational might to clear their orbits of other asteroids.
At 588 miles (945 km) across Ceres is about as big as Texas or a quarter as wide as the full moon. It’s a dark, ice-rich object that currently shines at magnitude 7, putting it within easy range of 35mm and larger binoculars. Whether binoculars or telescope, Ceres is too far away to look like anything more than one of the sky’s many fainter stars.
By good fortune, the dwarf planet just passed its opposition on May 26 and is now closest to the Earth for the year. It’s also easy to find thanks to Jupiter which shines a fist-and-a-half (15°) to the lower left of Ceres. To find this pinprick of light first locate Jupiter, which looks like a brilliant “star” in the southeastern sky around 10:30 p.m. this month. From Jupiter, slide a fist to the right to the bright, orange-red star Antares (an-TAR-eez) in the constellation Scorpius. If you look about 8° (a little less than a fist) to the right and a bit above Antares you’ll see a vertical row of three bright, equally spaced stars. That’s the head of the scorpion.
Point your binoculars at the topmost star of the trio, Graffias. Ceres lies about 3.5° degrees above Graffias. If you place the star in the bottom of your binocular field of view, Ceres will be just above the center. Confirm that it’s the dwarf planet by noting the pattern it makes with the stars near it. The map above shows stars as white-on-black, but if you prefer a more printer-friendly black-stars-on-white version, click here.
Once you’ve found Ceres, you can return the next clear night and make a discovery — it moves! Each night, the dwarf planet slips slowly westward (to the right) following along the arc drawn on the map. I like to make little stick figures connecting Ceres into triangles or squares with other stars in the field of view. When I return the next clear night, its movement will have stretched or bent my mini-constellation out of shape, making it easy to follow.
Wrapped into that stellar point is an amazing world of its own with tens of thousands of craters, some dotted with white, salty spots marking the locations of ancient briny-water seeps from below the crust. The dwarf planet is rich in clay and has a rocky core and ice-rich mantle. Ceres spins once every 9 hours and takes 4.5 years to go around the sun.
Much of what we know about Ceres comes through the eyes and instruments of NASA’s Dawn spacecraft which orbited the little orb between 2015 and 2018. Check out this wonderful album of photos taken during the mission.
I hope you get to see this interesting object with your own eyes while it’s bright and the weather fine.