Asteroids. Minor planets. Dwarf planets. The distinction is blurry even to some astronomers. No matter: three of the largest and most famous are making headlines this week.
One of the brightest asteroids, Vesta (525 km or 326 mi), “meets” the dwarf planet Ceres (950 km or 590 mi) just above the bright star Spica in the constellation Virgo. Vesta and Ceres are two of the four original big asteroids discovered at the start of the 19th century it is rather rare for them to “meet” in the same small piece of sky while also being easily visible through backyard telescopes. Both are unique. Vesta is the only asteroid that sometimes reaches nakedeye visibility, thanks to being whiter than any other. Ceres is spherical, possibly contains a thin atmosphere like Pluto, and, also like Pluto, is now officially classed as a “dwarf planet.”
Pluto demoted from a “planet” to a “dwarf planet” in 2006, reaches its opposition on July 4 when it is opposite from the Sun in our sky. Opposition always occurs on or within a few days of its very closest approach. It will not come this close again for more than two centuries. Moreover, next July the New Horizons spacecraft will finally zoom past Pluto after nine years of traveling from Earth it was the fastest ever spacecraft. So this is the final Pluto “opposition” in which that tiny world will most likely retain its mysteries.
Slooh will highlight the two dwarf planets along with asteroid Vesta on Thursday night, July 3rd, starting at 5:00 pm PDT / 8:00 pm EDT / 00:00 UTC (7/4), live from Slooh observatories located in the northern and southern hemispheres. The northern hemisphere observatory is located off the west coast of Africa, at the Institute of Astrophysics of the Canary Islands, and the southern hemisphere observatory is located at the Pontificia Universidad Católica de Chile (PUC) near Santiago.
Viewers can watch the broadcast free on Slooh.com. The image stream will be accompanied by discussions led by Slooh host Geoff Fox, Slooh astronomer Bob Berman, and Slooh observatory engineer Paul Cox. Viewers can follow updates on the show by using the hashtag #Sloohdwfplanet.
While 7th magnitude Vesta is easily viewable through binoculars, Ceres at magnitude 8.5 is more challenging; both require using good astronomical charts. As for Pluto, which is only 2/3 the size of our Moon, even experienced backyard astronomers often find its faint 14th magnitude a major challenge through backyard telescopes: It is a thousand time fainter than the dimmest nakedeye stars.
“Pluto remains a popular world,” says Slooh astronomer Bob Berman. “And the public is still unhappy with the decision to demote it from the ranks of major planets. One reason is its shared name with Walt Disney’s only nonspeaking character. It’s not wellknown, but that lovable dog was originally named Rover in an earlier cartoon. In 1931, the Disney folks decided to exploit the global publicity of that newly found planet, and changed the character’s name.”
Added Berman, “This first week of July marks Pluto’s closest approach until the 23rd century, and its final one before its secrets are finally revealed by New Horizons craft, which makes this a compelling
‘opposition.’ And Ceres and Vesta coming together in Virgo is very cool too. Having this threeforone special at the Slooh community observatory makes for a unique program.”