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Huge Asteroid Pallas Visible From Earth


Asteroids are not as well behaved as planets, and their orbits are often far from the plane of the ecliptic. This is clearly the case with Pallas, because it reaches opposition in the unlikely constellation of Serpens Caput, very close to Corona Borealis, the Northern Crown. This is a pretty circlet of stars just to the left of Arcturus in northern hemisphere skies.

To spot Pallas tonight, look for the brightest star, called either Alphecca or Gemma, in Corona Borealis. Pallas is an 8th magnitude object just south of this star. [How to spot Pallas.]

If you make a sketch of the star field with binoculars tonight and repeat this over the next few nights, you'll clearly see which "star" is moving: This is the best way to identify an asteroid. Alternatively, use planetarium software to make a chart of the area of Corona Borealis and identify Pallas from that. Binoculars or a small telescope are essential for spotting this faint object.

Pallas is the second largest asteroid, 326 miles (524 km) in diameter. Or is it? Vesta might dispute this claim for, although it's slightly smaller in diameter at 318 miles (512 km), it is much more massive due to a much higher density.

Legacy of Pallas

Pallas' history is closely tied with the discovery of the first known asteroids centuries ago.

In the year 1800, the solar system was a pretty simple place. There was the newly discovered planet Uranus, making a total of seven planets, plus the sun, moon, and a number of comets.

Within a few years, the solar system became a much more complicated place. On the first day of the new century, January 1, 1801, Giuseppe Piazzi discovered a new "planet" which he named Ceres. A little over a year later, on March 28, 1802, Heinrich Olbers discovered another new "planet" which he named Pallas after Pallas Athena, another name for the goddess Athena.

Olbers is most famous for his paradox, which states that the darkness of the night sky conflicts with the supposition of an infinite and eternal static universe.

These discoveries were followed by Juno in 1804 and Vesta in 1807, the latter also being discovered by Olbers.

Astronomers were divided as to whether these tiny objects were planets or something different, called "asteroids" by some because they were all so small that they appeared as stars in the telescopes of the day. It was nearly four decades before a fifth asteroid was found.

That find was almost totally overshadowed by the discovery a year later of the planet Neptune, and asteroids have been relegated to a minor role in the solar system ever since. We now know thousands of them, but the four discovered in the first decade of the 19th century remain the largest and brightest.


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