Ceres and Vesta—two of the biggest and brightest asteroids in the solar system—offer sky-watchers a record-breaking rendezvous as a treat over the holiday weekend.
Not since their discovery more than 200 years ago has anyone observed these two giants of the main asteroid belt pair up so closely in the heavens.
Since spring, keen-eyed sky-watchers using nothing more than binoculars or small telescopes have followed the cosmic duo. The two asteroids have flown in tandem, looping across the Virgo constellation now visible in the southwestern evening skies.
While they are beginning to fade (Ceres shines at magnitude 8.5 and Vesta at magnitude 7.2), the best part of the celestial show happens on the evenings of July 4 and 5, when the pair reach their closest moments. Overnight, the two asteroids will appear separated by only ten arc-minutes, equal to one-third of the width of the moon’s disk.
There is no need to fret about any collision between them, however. Their proximity in the sky is simply an illusion, created by their positions relative to each other and to Earth. In reality, some 46 million miles (74 million kilometers) of space will separate the two asteroids.
While Ceres, at 585 miles (940 kilometers) wide is nearly two times larger than Vesta, it appears fainter to us because it is farther away and has a much darker surface.
After July 5, the two will start to drift apart; however, they will remain within 5 degrees of each other (within a binocular’s field of view) until July 11.
See for Yourself
Start your asteroid hunt with the bright beacons of Mars and Spica. They will help point the way to the much fainter field of stars right above them where your targets lie.
Also helping to make it easy, the faint naked-eye star, Zeta Virginis, will be only 1.5 degrees northeast of the asteroids.
Astronomy.com offers a detailed finder’s chart and a tip to help you confirm you have bagged Ceres and Vesta: Sketch the positions of a handful of stars around what you suspect are the asteroids through the telescope. Look again in the same field of stars the next night or two. The two that have moved are the asteroids.
And while you are looking at these two giant space rocks, ponder the spacecraft nearby in the same field of view. NASA’s Dawn mission first visited and mapped Vesta in unprecedented detail in 2011 and 2012. It is now on its way to a historic encounter with Ceres in March 2015.
If you end up clouded out or don’t have binoculars to catch this unique sky show, then Slooh.com will be broadcasting the historic asteroid encounter live online from their observatory in the Canary Islands off the coast of West Africa. The webcast begins on July 3 at 8:00 p.m. EDT (00:00 UTC).