Categories: AsteroidsAstronomyDawnObservingSkywatchingSolar System

Ceres and Vesta Converge in the Sky on July 5: How to See It

Ceres and Vesta are converging in Virgo not far from Mars and Spica. On July 5, the duo will be just 10' apart and visible in the high power telescope field of view. Positions are shown every 5 days for 10 p.m. EDT and stars to magnitude +8.5. Created with Chris Marriott's SkyMap software

I bet you’ve forgotten. I almost did. In April, we reported that Ceres and Vesta, the largest and brightest asteroids respectively, were speeding through Virgo in tandem. Since then both have faded, but the best is yet to come. Converging closer by the day, on July 5, the two will make rare close pass of each other when they’ll be separated by just 10 minutes of arc or the thickness of a fat crescent moon.

Vesta (left) and Ceres. Vesta was photographed up close by the Dawn spacecraft from July 2011-Sept. 2012, while the best views we have to date of Ceres come from the Hubble Space Telescope. The bright white spot is still a mystery. NASA will plunk Dawn into orbit around Ceres next February. Credit: NASA

Both asteroids are still within range of ordinary 35mm and larger binoculars; Vesta is easy at magnitude +7 while Ceres still manages a respectable +8.3. From an outer suburban or rural site, you can watch them draw together in the coming two weeks as if on a collision course. They won’t crash anytime soon. We merely see the two bodies along the same line of sight. Vesta’s closer to Earth at 164 million miles (264 million km) and moves more quickly across the sky compared to Ceres, which orbits 51 million miles (82 million km) farther out.

Ceres and Vesta lie near an easy naked eye star, Zeta Virginis, which forms an isosceles triangle right now with Mars and Spica. The map shows the sky around 10 p.m. local time tonight facing southwest. Stellarium

Right now the two asteroids are little more than a moon diameter apart not far from the 3rd magnitude star Zeta Virginis. Happily, nearby Mars and Spica make excellent guides for finding Zeta. Once you’re there, use binoculars and the more detailed map to track down Ceres and Vesta.

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Virgo will be busy Saturday night July 5, 2014 when the waxing moon passes about 1/2 degree from Mars as Ceres and Vesta squeeze closest. Stellarium

In early July they’ll look like a wide double star in binoculars and easily fit in the same high power telescopic view. Vesta has always looked pale yellow to my eye. Will its color differ from Ceres? Sitting side by side it will be easier than ever to compare them. Vesta is a stony asteroid with a surface composed of solidified (and meteoroid-battered) lavas; Ceres is darker and covered with a mix of water ice and carbonaceous materials.

On the night of closest approach, it may be difficult to spot dimmer Ceres in binoculars. By coincidence, the 8-day-old moon will be very close to the planet Mars and brighten up the neighborhood. We’ll report more on that event in a future article.

With so much happening the evening of July 5, let’s hope for a good round of clear skies.

Bob King

I'm a long-time amateur astronomer and member of the American Association of Variable Star Observers (AAVSO). My observing passions include everything from auroras to Z Cam stars. I also write a daily astronomy blog called Astro Bob. My new book, "Wonders of the Night Sky You Must See Before You Die", a bucket list of essential sky sights, will publish in April. It's currently available for pre-order at Amazon and BN.