Asteroids: Take a Number

Italian monk, mathematician, and astronomer Giuseppe Piazzi (1746-1826) discovered an unexpected 8th magnitude object in Taurus near Mars and the Pleiades at around 8:00 p.m. on January 1, 1801 at his observatory in Palermo, Sicily. Thinking it a comet, he recorded the position of the object over several nights, until illness forced him to quit on February 11, just a few days after the object passed fairly close to Mars. By early May, the object was too close to the Sun in the western sky to observe, and Piazzi despaired of ever recovering the object. The now-famous 24-year-old German mathematician Carl Gauss (1777-1855) came to the rescue. Gauss used Piazzi’s positions to determine an orbit for Ceres (so named by Piazzi) and predicted from the scant data its future positions when it would once again be visible in the night sky. Ceres was recovered only a half-degree away from its predicted position by Hungarian astronomer Franz Xaver von Zach (1754-1832) on December 7, close to Denebola and not far from a close conjunction of the planets Jupiter and Saturn, and then confirmed after a long stretch of cloudy weather on December 31, 1801. The German amateur astronomer Heinrich Olbers (1758-1840) found Ceres at Bremen two days later on January 2, 1802. Olbers (of Olbers’ Paradox fame) discovered the second asteroid, Pallas, on March 28, 1802. Many, many more asteroids have been discovered since then. They are sequentially numbered, originally in order of their discovery date, but nowadays in order of their receiving a precise orbit determination.

Fast forward.

The names of asteroids 998 through 1002, discovered between August 6-15, 1923, have special significance.

998 Bodea – named in honor of German astronomer Johann Elert Bode (1747-1826), whose empirical relationship of the distances of the planets (Titius-Bode Law) indicated that there should be a planet between the orbits of Mars and Jupiter, touching off a massive search led by von Zach for a new planet.

999 Zachia – named in honor of Franz Xaver von Zach, who published Piazzi’s observations and recovered Ceres after Gauss’ predicted positions.

1000 Piazzia – named in honor of Giuseppe Piazzi, who discovered the first asteroid, 1 Ceres.

1001 Gaussia – named in honor of Carl Friedrich Gauss, who predicted the position of Ceres so it could be recovered.

1002 Olbersia – named in honor of Heinrich Olbers who was the second person to recover Ceres and the discoverer of the second asteroid, 2 Pallas (and 4 Vesta, by the way).

Fortunately, German astronomer Johann Daniel Titius (1729-1796) finally did get an asteroid named after him as well: 1998 Titius, discovered on February 24, 1938.

As of August 19, 2019, 796,422 minor planets (asteroids, trans-Neptunian objects, etc., but not including comets) have been discovered, but only 541,128 have orbits that are well-enough determined that they have been given a minor planet number. When a minor planet is first discovered, it is given a provisional designation based on the date of discovery. For example, 2019 PE3 was discovered during the first half of August 2019. After enough high-quality astrometric data has been collected to determine an accurate orbit, the minor planet is assigned a number. For example, minor planet 1996 TB1 was discovered by IOTA member George Viscome on October 5, 1996. It received a number, 35283, in 2000, and it received a name, Bradtimerson, earlier this year (2019). George submitted the name to the IAU after Brad Timerson, mentor and inspiration to many of the current crop of asteroid occultation observers, passed away on October 17, 2018. So we now have 35283 Bradtimerson.

The counts in the paragraph above show us that 67.9% of the minor planets that have been discovered have been assigned a number. Of these, only 21,922 (4.1%) have received a name.

Many asteroids have been given interesting or unusual names. Excluding the many fine individuals (real, not fictional) who have an asteroid named after them, here are a few of my favorites. There are a few here that are actually named after a person, but the minor planet name has a meaning beyond just the person’s name.

Remember, these are real places that will be visited someday. Oh, to be so lucky!

Lots of asteroids are awaiting names. Can you come up with some interesting, entertaining, or poetic ones? Give it a try, check this list or do a search here to make sure it is new, and then post a comment here and I’ll probably include your ideas in this article, giving you credit, of course. Be creative!

To get you in the spirit, here are a few names I’ve come up with:

  • Botanica
  • Distantia
  • Eternium
  • Gandalf
  • Luminaria
  • Morethanamote
  • Portentia
  • Symphonica

Have fun!

Cometary Tails

A comet’s ion/plasma/gas tail points directly away from the Sun. A comet’s dust tail deviates somewhat (and sometimes a lot) from this, falling behind the comet along its orbital path around the Sun.

For the best view of either tail, our line of sight should be perpendicular to the length of the tail. However, that seldom happens, and we are viewing the tails with some degree of foreshortening. The orientation of the gas tail is called the phase angle, and it is the Sun – comet – observer angle.

A phase angle of 0° indicates we are looking straight down the tail of the comet (maximum foreshortening) with the head being oriented closest to the observer.

A phase angle of 90° indicates that our line-of-sight to the comet is perpendicular to the Sun-comet line, so we are viewing the comet’s gas tail with no foreshortening.

A phase angle of 180° indicates that we are again looking straight down the gas tail of the comet (again, maximum foreshortening) only this time the tail is closer to the observer and the head further away. Of course, the only time this orientation could happen is when the comet is transiting the Sun, thus rendering it essentially unobservable.

Phase angles of 0 to 90° mean that the comet head is closer to the observer than the tail; angles of 90 – 180° mean that the comet’s tail is closer to the observer than the head.

Here’s a table showing the phase angle, and some other information, for currently-observable comets brighter than 15th magnitude as seen from Earth. The column labeled Elongation indicates the Sun – observer – comet angle. In other words, the angular separation between the Sun and the comet.

A comet that is farther from the Sun than the observer can never have a phase angle as great as 90°, but a comet that is closer to the Sun than the observer can. Looking at the diagram above and considering a comet in a circular orbit around the Sun (highly unlikely, I know, but bear with me) and closer to the Sun than the observer, the phase angle would be 90° when the comet is at greatest elongation.

Incidentally, comet designations that have a number followed by the letter “P” (such as 29P, 68P, and 260P) are periodic comets (more precisely described as short-period comets), defined to be comets with orbital periods of less than 200 years or that have been observed at more than one perihelion passage.