NEWS & EVENTS
Vesta Fiesta > Observing Vesta
You can see Vesta for yourself—but it's a challenging object to find. Though it is visible to the unaided eye in a very dark sky—in a remote location, far from city lights—even there, it would only look like a faint star, one among a whole sky filled with stars. A good pair of binoculars, or a telescope, can give you a better view, but it will still look like a star. The trick is to know where to look. Despite the challenge, this summer is actually one of the best times to try to find Vesta, and the Dawn Mission encounter makes it all the more special.
What Does Vesta Look Like?
Vesta looks like a star, even in a large telescope. That's why Vesta, Ceres and the other celestial bodies between Mars and Jupiter were called "aster-oids." The very name means "star-like." Astronomers talk about the magnitude of an object to describe its brightness. Bright stars are around 1st magnitude. The very limit of the human eye is around 6th magnitude. (Brighter objects have lower magnitudes—a bit like a ranking system.)
Vesta will be around magnitude 5.6 on August 6. That puts it close to the limit of human vision under optimal conditions. If you are anywhere near a city or town, you'll need binoculars or a telescope. You won't know you're looking at Vesta by its star-like appearance, but only by knowing its exact position. (See below.)
When to Look:
On the weekend of August 6 and 7, Vesta reaches “opposition.” That means it’s roughly opposite the sun in the nighttime sky, so it rises around sunset, reaches its highest point in the middle of the night (around 1 am daylight savings time), and sets around sunrise. The good news is that it’s up in the sky all night.
If you’re using a binocular or telescope, be sure to never look at the sun.
Where to Look:
Vesta is in the constellation Capricornus this year. If you can find this constellation in the sky, your chances for finding Vesta are much improved. Capricornus does not have any particularly bright stars, and you need a dark sky to pick out its pattern. Also, for many observers in the United States, this constellation is low in the sky, toward the southern horizon.
How to Find Vesta:
There are a number of great resources on the web, with information and even printable sky charts, showing the position of Vesta. Ceres rises just after Vesta this month, and while more faint, will be visible as well to telescopes. A really good site is Sky and Telescope Magazine. To find instructions and a detailed map, visit the Ceres and Vesta in 2011 page to download a full-page printable chart for Ceres and Vesta in PDF form. Visit Astronomy Magazine's website to print out your own sky chart customized to your geographic location.
You'll need some orientation in the night sky to find Capricornus in the first place. A Planisphere, or Star Wheel, is a useful tool. If that's not available, try http://www.heavens-above.com. This allows you to print star maps, and has additional information about Vesta. If you choose to register, it's free, with no obligation at all.
If you're familiar with coordinates, or have a telescope that uses them, Vesta will be in the following area on August 6 and 7:
Right Ascension: 21 hours, 6 minutes
Declination: -23 degrees
For more detailed coordinates, and to see how they slowly change with time, try the Jet Propulsion Lab HORIZONS site. Input "Vesta" for your target object.
How High in the Sky?
To give you an idea of the peak altitude of Vesta during the night, look at the “declination” above. It’s –23 degrees, which means that Vesta is right overhead, at the zenith, for an observer at 23 degrees south latitude in the middle of the night. At the equator, Vesta peaks, or ‘culminates’ at 67° altitude. For an observer at 34° (say, Los Angeles), Vesta culminates at 33°. For an observer at 41° latitude (say, New York), Vesta culminates another 7° lower, at 26°. When Vesta reaches this peak altitude, you’d be looking for it toward the south horizon. Earlier in the night, it would be found toward the southeast; later, it would be found toward the southwest.
If you wish to see Vesta, it's a good idea to start getting acquainted with the constellations beforehand. You might also look to see if there's an astronomy club in your area. It shouldn't be difficult to encourage those who know the sky to go for a look at Vesta. Starlike or not, Vesta is a truly significant object in the sky—and a world that Dawn is now revealing to us.