Vesta, aka 4 Vesta, the third largest of the asteroids within the main asteroid belt between Mars and Jupiter reaches opposition Sunday 13 April. Two days later, 15 April, the closest Dwarf Planet to Earth, the former asteroid Ceres also reaches its opposition. Opposition is an arrangement with any outer planet or asteroid that is further from the Sun than the Earth. At opposition the Earth is between, in this case, either Vesta or Ceres, and the Sun. At opposition, like the full Moon, a planet or asteroid rises at sunset and is above the horizon all night and then sets at sunrise.
Ceres, with an average diameter of 590 miles (950 km), as an asteroid was the largest and now as a dwarf planet is among the smallest if not the smallest object with enough mass to become round and thus qualify for a lateral promotion to dwarf planet status. Vesta has an average diameter of 525 km (326 miles ) and was the fourth asteroid discovered, in 1807. Vesta was also just recently visited and explored from orbit by NASA’s Dawn spacecraft. That spacecraft left orbit around Vesta in September 2012 and it is now heading for arrival at Ceres during the spring (northern hemisphere) of 2015. Vesta is also the brightest asteroid as seen from Earth and so the next few weeks offer an opportunity to perhaps see this asteroid and Ceres as they both move into and then past opposition and then moving in retrograde, westward.This animated graphic shows the westward motion of Vesta and Ceres as the two pass by several stars, some of which have a magnitude around Vetsa’s 5.39 and Ceres’s 6.5.
Neither Ceres nor Vesta move fast enough to see any change in their position relative to any nearby ‘reference’ stars for at least a day or so. See if you can catch a ‘star’ changing its position relative to other stars by drawing a star chart of the stars you see in the field of view of your binoculars or telescope eyepiece. Repeat the drawing the next night, or wait another night. Do this a few times and by comparing your drawings you may find one of the dots you made for stars has shifted its position. That is the asteroid. Congratulations!Throughout this period the Moon will change from its waxing gibbous phase, pass through the Earth’s shadow for a total lunar eclipse, then begin its waning gibbous phases all the while passing past the asteroids Vesta, Ceres, Mars, Saturn, and a bunch of other celestial delights.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.