Vermin of the Skies
by John Hlynialuk
On my astronomy calendar, the new year is marked by the anniversary of a night over 200 years ago (1801) that created a crisis in planetary astronomy. It was not immediately recognized as such, and the alarms were only heard in astronomical circles at first. The general public was mostly unaware that their universe was changing.
The event was the discovery of Ceres, an object that was called a “planet” for a while, then an “asteroid” and now is referred to as a “minor solar system body”.
Guiseppe Piazzi, an Italian astronomer celebrated the first night of 1801 by discovering an unusual moving speck in a place where astronomers expected planets to be, and it came to be named Ceres (the Roman goddess of agriculture). Discoverers are allowed to suggest names, although the International Astronomical Union has final approval. There is some leeway in suggested names, however, and it’s OK (and a great idea) to name an asteroid after your spouse, -several discoverer’s wives have been immortalized in the heavens. However, the IAU will not allow naming a new asteroid or comet after your cat, for ex. Neither can anyone name a star after a loved one, not officially anyway. (Those websites are, in fact, a scam).
Twenty years before Piazzi’s discovery, on March 13, 1781, William Herschel added a 7th planet, Uranus, to the list so Ceres raised the planet count to eight.
Then in rapid succession, three additional “planets” was discovered, Pallas in 1802, Juno in 1804 and Vesta in 1807. The count stayed at 11 until 1845 when the astronomical “cup” overflowed.
In 1845 Astraea was discovered and the planet number went to twelve. Now things started to get complicated. In September 1846, an object was discovered that was different. The previous discoveries were star-like objects between the orbits of Mars and Jupiter, but this one was the most distant object ever observed. Furthermore, large telescopes showed that the object had a disk and colour similar to that of Uranus. Planet 13 (actually Neptune) was more like planet 7 (Uranus) than planets 8 thru 12.
From 1847 on, new “planets” were discovered at the rate of about one a year and astronomers uncharitably started to refer to these objects as the “vermin of the skies”, -not because they were ugly, (which they are -think debris from the exploding Death Star in Star Wars spreading out through space), but because there were so many of them.
The situation was resolved when William Herschel suggested that these objects should be put into a separate category of small “star-like” bodies that would be called “asteroids”. It was an intelligent suggestion especially as the numbers of asteroids continued to grow. There were enough ways to challenge students without asking them to memorize (in proper order) hundreds of new “planets”.
Astronomers now list more than 200 asteroids over 100 km in size, Ceres, the one that started it all, is 945 km across and Vesta is 545 km in diameter. The IAU recognizes 20 364 with names and there are thousands more that are simply given catalogue numbers. In all, there may be several million asteroids, but thankfully, most orbit between Mars and Jupiter and seldom stray to the vicinity of Earth to pose a danger.
In June 2014, both Vesta and Ceres were in the same part of the sky near the star Heze in Virgo.
Image was taken with a Canon 60Da with a zoom telephoto set at 285 mm focal length f/5.6, 30 s exposure (on a tracking telescope) ISO 2000. The image is a crop from the original and shows stars down to about 9th magnitude. Vesta magnitude was about 6.1, Ceres was at 7.3 .
Photo Ⓒ 2014 by J.Hlynialuk
Asteroid 4Vesta is bright enough to be seen with the naked eye but binoculars make the task easier. See it for yourself over the next few months, -the finder chart shows where to look. Join the two brightest stars of Gemini, -Castor and Pollux- and extend the line down (eastwards) and you are in the right general area. Vesta should be the brightest object in view, but there is only one certain way to identify it. Make a quick star sketch (or take a photo) and then come back in a few days to see which “star” has moved. (This is how Vesta was originally discovered). Spot Vesta and you can add a named asteroid to your life list of astronomical objects. Only 20 363 more to go.
Detailed finder charts (both Vesta and Ceres) and photo hints are under the CHARTS & FORMS tab. Good luck hunting “minor solar system bodies” !