Have you ever seen an asteroid? They look exactly like stars. That’s because nearly every one of approximately 822,000 known objects are too small and far away to show a shape. The name’s a giveaway. The “aster” in asteroid is Latin for “star.” All asteroids circle the sun similar to the planets but are concentrated in two primary regions — the main asteroid belt between Mars and Jupiter and the Kuiper Belt beyond Neptune. Asteroids in the main belt are mostly made of rock while those in the outer solar system are rich in ices like water.
Vesta orbits within the main belt at an average distance of 219 million miles (353 million km) — 2.3 times Earth’s distance from the sun — every 3.6 years. At 326 miles wide (525 km) you could drive across it in under 6 hours at freeway speeds. Vesta is one of the most reflective asteroids and the brightest visible from Earth. During favorable approaches it can become bright enough to see with the naked eye.
This month Vesta reaches opposition on Nov. 12, when it’s closest to Earth for the year. And it won’t disappoint. For the next couple weeks the minor planet (another name for an asteroid) will shine around magnitude 6.6, only a half a magnitude below the naked-eye limit, and make an easy catch in almost any pair of binoculars magnifying 7x and up.
You’ll find the mobile point of light in western Taurus the Bull where it shares a border with Cetus the Sea Monster. Sounds like dangerous territory but Vesta proceeds apace. Tonight (Nov. 5) and the next few nights are ideal for tracking the minor planet because it passes close to the 3rd magnitude naked-eye star Omicron (ο)Tauri. Center that star in binoculars and Vesta will share the same field of view. From here it moves west into Cetus in the vicinity of that constellation’s brightest star, Menkar or Alpha (α) Ceti.
You’ll be watching for what looks like a star slowly march to the west a fraction of a degree each night. You’ll also get to see one of the most unique objects in the solar system — Vesta is the only known protoplanet of the type that coalesced to form the terrestrial planets. Protoplanets are different from most small, rocky objects because they were hot enough to evolve a denser, metal-rich core surrounded by a thick rocky crust. Astronomers say Vesta is differentiated in contrast to the simple “mixed bag” of materials found in uncooked, undifferentiated asteroids.
Moonlight will start to hamper your attempts at seeing Vesta in binoculars soon, so try to find it the next clear night. Moonless conditions return starting about Nov. 16. It’s fun to go for a “ride-along” on a bright asteroid using nothing more than binoculars and your imagination. May good weather prevail. For tons of great pictures of Vesta, check out NASA’s Vesta Photojournal.