This year the first of the major asteroids that we pass at opposition is the brightest, the only one you can possibly find with the naked eye: asteroid 4, Vesta.
Don’t forget to enlarge this picture if you can. The broad arrow on the equator shows how far the sky turns in one hour.
Here is the more detailed way to find Vesta with binoculars:
Click the “Astronomical Calendar 2017” tab above and go to the “Asteroids” page to see a space diagram, which shows how Earth is overtaking Vesta on the inside. A dashed line is the sight-line from Earth to Vesta at this date. Because Vesta is in the part of its orbit that is in the Gemini direction, we overtake it soon after our winter solstice.
I calculate the opposition date as Jan. 17 at 17h Universal Time, because I use the opposition in ecliptic longitude, as for the planets. You may see the date given slightly differently (Jan. 18) in other sources, such as the U.S. Naval Observatory’s Astronomical Almanac, because they use the opposition in right ascension.
The precise date of opposition doesn’t greatly matter: it is the middle of the rough span of time when a moving body is nearest and brightest. What matters more is that the Moon, with its interfering glare, was Full on Jan. 12, so it is now rising at about 10 PM, and will rise later on following nights.
So the good time for Vesta is really the two weeks starting now. It will fade by a magnitude, but be findable with binoculars in moonless evenings.
Though Vesta was only the 4th asteroid discovered (in 1807), it is the second largest (525 kilometers wide) after 1 Ceres and is the one that becomes brightest, because of being usually nearer in than Ceres and especially because of its high “albedo” or reflectivity: in other words, it has a light-colored surface. At this opposition it reaches magnitude 6.3 – just at or above the limit for the naked eye with a dark clear sky. It can at opposition be as dim as 6.6, or as bright as 5.4, as will happen in 2018 when perihelion and opposition are close together (May 10 and June 19). Ceres is usually a little dimmer than magnitude 7 at opposition and rarely becomes as bright as 6.7.
We now know a lot more about Vesta because NASA’s Dawn spacecraft was in orbit around it from 2011 July to 2012 September. Collisions billions of years ago knocked many pieces off Vesta, and some have rained onto Earth as meteorites of a recognizable kind.
There used to be a brand of matches called Vesta; the asteroid didn’t get its name from those, but from the Roman goddess, equivalent of the Greeks’ Hestia, one of the Olympian Twelve, virgin protectress of the hearth and home.
Not sure why Hestia gets connected with an asteroid but I guess she appears to be clean.
Starting with William Hershel’s 1781 discovery of a new planet — all the other planets had been known since antiquity — astronomers were faced with a new problem: what to call these newly discovered planets? Herschel called his planet “the Georgium Sidus” — the Georgian star, in honor of King George III of England, Herschel’s adopted homeland. Astronomers in other countries weren’t keen on that name, and for a while it was called “Herschel’s planet” or simply “Herschel”. Johann Bode in Herschel’s homeland of Germany suggested naming the new planets after Roman and Greek gods, as the ancients had done, and by 1850 the name “Uranus” was generally accepted for Herschel’s planet.
With the discovery of the first asteroid (Ceres) in 1801, and then more minor planets in what we now call the asteroid belt, the tradition of naming planets after Roman or Greek gods continued. Heinrich Olbers (who also pointed out what we now call Olbers’ paradox) discovered the second asteroid (Pallas) and the fourth, which he named Vesta. So that’s how Hestia got connected with an asteroid. And I, for one, am glad she is so honored.
By the way, the term “asteroid” was first proposed in 1802 by Charles Burney Jr., a British expert in the Greek language and the son of the poet Charles Burney, who was a friend of Herschel’s. The term “asteroid” was initially ridiculed by astronomers, and didn’t come into general use until about 1850.
The irregularity in the naming of the planets is that all of them are Roman except Uranus (Greek). The irregularity in the name of the first four minor planets is that all of them are Roman except Pallas (Greek).
The Greek goddess we usually refer to as Athena or Athene is frequently called in the Iliad by a mysterious double name, Pallas Athene; sometimes just Pallas. (Similarly, Apollo was called Phoebus Apollo.) There were various other figures, male and female, called Pallas in the mass of Greek legends; I think nobody really knows the reason for “Pallas Athene”, but explanations given were that Athene had killed a giant called Pallas, or mourned a friend called Pallas, or had a parent called Pallas. It would have been more consistent if Olbers had named the second asteroid for Minerva, who was the goddess the Romans regarded as equivalent to Athene.
Thanks Guy. For the past week and a half I’ve been enjoying watching Vesta moving retrograde against the stars of western Cancer, using hand-held 8×42 binoculars from my light-polluted urban back yard. During breaks in the rain and clouds during the two weeks before my first certain observation of Vesta on the evening of January 5, I was learning the star field, using the Sky and Telescope Pocket Sky Atlas. I’ve now seen Vesta three times, when the weather cooperated, most recently last night and the night before, and she is moving quite noticeably from one night to the next. Having seen her a couple of times previously, last night it was easy to see which sixth magnitude “star” was really “star-like”, an “aster-oid”.
I’ve never seen Vesta with my unaided eyes — maybe next year? Because she’s the brightest asteroid I always make a point of looking for her around her opposition. Like sixth magnitude Uranus, Vesta is hard enough to find and recognize to give me a sense of accomplishment, but not so hard as to be frustrating.
I also appreciate Vesta’s archetypal energy as the goddess of hearth, home, and family, and the classical tradition of each household keeping a Vestal shrine, whether elaborate or modest.