There’s Nothing Like A Spring Morning On Vesta

Astronomers combined 146 exposures taken by NASA’s Hubble Space
Telescope to make this 73-frame movie of the asteroid Vesta’s
rotation. Vesta completes a rotation every 5.34 hours. Credit: NASA / ESA

Just 280 days to go. That’s when the Dawn probe will enter orbit around Vesta, the second largest asteroid in the main asteroid belt. In the meantime, the Hubble Space Telescope has been pressed into service taking hundreds of closeup photos of 329-diameter asteroid to help refine what we know about its spin and axial tilt. When the probe arrives next July, it will examine and photograph Vesta’s surface from an orbit that circles around the poles. Instruments on board include infrared and visible light cameras, spectrometers to determine what minerals make up Vesta’s crust, and a device that indirectly probes the asteroid’s interior by measuring its gravity field. Scientists are interested in asteroids because they were the original building blocks of the planets. The more we can learn about them, the better we’ll understand Earth’s origin and early history.

Vesta's about 220 million miles from the sun. That distance, combined with its small size, means that the Hubble Space Telescope can only distinguish the largest features on asteroid's surface. The dark areas are probably basaltic crust, the pink is surface dust and soil. Credit: NASA/ESA

After studying hundreds of new Hubble images, astronomers discovered that Vesta’s poles are tipped four degrees more to the asteroid’s east than expected. Since seasons are determined by the tilt of a planet’s or asteroid’s axis, the added tip means that the difference in seasons between the northern and southern hemispheres will lag about a month behind original predictions. Christopher Russell, Dawn’s principal investigator, explains:  “Because our goal is to take pictures of the entire surface and measure the elevation of features over most of the surface to an accuracy of about 33 feet, or the height of a three-story building, we need to pay close attention to the solar illumination. It looks as if Vesta is going to have a late northern spring next year, or at least later than we planned.” You’ll recall that it’s the tip of a planet’s axis that determines the height of the sun in the sky and the length of its seasons.

Comet Hartley 2 and the Double Cluster last night from Austria. Credit: Michael Jaeger

Friday and Saturday nights, Comet Hartley 2 scooted by the Double Cluster in Perseus. We ran a photo of that yesterday, but overnight, I received one of the finest pictures I’ve seen of the event. It was taken by the noted Austrian comet observer and photographer Michael Jaeger. This guy’s work is astoundingly good. Click on the image to see the mouth-watering version.

This map shows the sky as you face south around 2:30 p.m. today. Look for the thin lunar crescent with either your naked eye or, better, with binoculars. Once you've found the moon, the crescent Venus will be a short distance below and to its right. The pair is about 20 degrees or two outstretched fists above the horizon at the time for the northern states, but higher up for the southern U.S. Created with Stellarium
Venus photographed with a point and shoot camera through a small telescope at 2 p.m. today. North is up. Photo: Bob King

Some of you who’ve tried to find Venus in daylight and been frustrated may want to try again with the help of the crescent moon this afternoon. While the moon will be thin,  it might be easier to see than a point of light in the blue. Venus will be about 2 degrees below and right of the moon when the pair is due south around 2:30 p.m. your local time.  Haze-free, deep blue skies are best for making this observation.

I wanted to point out an error, since corrected, of the position of Mira on yesterday’s map of the constellation Cetus. I accidentally confused it with a star close to the same position. My apologies. Let us know how your whale hunt goes!