Comet Observations – Sept 29

This past weekend I spent Sunday night at the University of Arizona’s Kuiper 1.54-m (61″) telescope where the 1.54-m (61″) is the diameter of the primary mirror. This telescope is located in the Catalina Mountains north of Tucson, Arizona. The goal of the night was to learn more about a Near-Earth asteroid that could be a good target for a future spacecraft mission. During the course of the night, I was able to observe a few interesting comets. All images were taken with a R-band filter with North to the top and East to the left.

Comet 205P/Giacobini

This comet was lost for 111 years before being re-discovered last month. Two small pieces of the comet have also been observed and this may mean the comet is brighter than it usually gets. Two older posts go into more detail on the discovery and splitting of this comet.

The images from Sunday evening show the main comet (component A) shining at R magnitude 12.6. At this brightness, only the most advanced amateurs with very large backyard telescopes can see this comet without a digital camera (CCD). The small comet in front (to the right in the image below) is component B. At R magnitude 18.6, it is 250 times fainter than the main comet. A third component was discovered a few weeks ago (component C) but I was unable to see it, though I’ll have to admit that I didn’t try very hard to find it.

Comet 29P/Schwassmann-Wachmann 1

Schwassmann-Wachmann 1 (SW1) is one of the most interesting comets out there. Most comets are on long elliptical orbits around the Sun that take them close to the Sun and then very far from the Sun. Usually comets are brightest and most active when they are closest to the Sun. SW1, on the other hand, is on a near-circular orbit that only varies from 5.7 to 6.3 AU from the Sun. More importantly, its orbit always keeps it further from the Sun than Jupiter. Most short-period comets with periods less than ~10 years only get out as far as Jupiter and are barely active at that distance. The fact that SW1 is always active at these distances is rather amazing.

The comet was discovered in 1927 by the same German team that found Comet Schwassmann-Wachmann 3 which was observed in 1000s of pieces back in 2005. Most of the time, SW1 is rather faint at ~18th magnitude. Every few months, the comet experiences a sharp increase in activity (we call this an outburst) and rapidly increases in brightness. It currently is experiencing one of its biggest outbursts and shines with a R magnitude of 10.9, bright enough for advanced observers with large backyard telescopes.

The image below is a straight forward with no image processing other than the usual techniques to fix up problems inherent to the camera and telescope (bias subtraction and flat fielding).

The next image was processed to bring out more detail in the coma of SW1. A technique akin to an unsharp mask was used. A number of possible jets (the straight lines radiating from the center, or nucleus, of the comet) are seen. A shell of material is also visible to the south of the nucleus. The material will slowly expand with time and the comet will dim until the next outburst.

C/2007 W1 (Boattini)

This comet was a nice binocular comet this past summer when it passed within 0.85 AU of the Sun and 0.21 AU of the Earth. It is now outbound and rapidly fading. The comet was discovered by Andrea Boattini of the Tucson-based Mount Lemmon Survey on 2007 November 20. The Mount Lemmon Survey observes with a telescope just up the road from the one I used to take these images. Comet Boattini is a long-period comet and will not return for many tens of thousands of years.

Comet P/2008 L2 (Hill)

Rik Hill found this back on June 12 of this year. The comet is on a 14.7 year orbit which brings it within 2.3 AU of the Sun and out as far as 9.7 AU. That’s almost as far as the orbit of Saturn. Rik works for the Catalina Sky Survey (same group but different telescope as the Mount Lemmon Survey) and used the Catalina schmidt telescope which is located across the parking lot from the scope I used. It’s measured R-band magnitude was 15.4.

Comet P/2008 Q2 (Ory)

Comet Ory is also a short-period comet with a 5.8 year period and an orbit that takes it between 1.4 and 5.1AU. Michel Ory, an amateur astronomer from Delemont, Switzerland, found this comet on August 27. This is Michel’s 1st comet though he has 2 supernovae to this credit. The comet’s brightness was measured at R magnitude 14.9.

Comet Giacobini in Pieces

Astronomers at Cordell-Lorenz Observatory in Sewanee, TN have reported that Comet Giacobini has split into at least three pieces. Comet 205P/Giacobini had been lost for ~111 years until it was rediscovered 2 weeks ago (see the previous post on Giacobini).

The detection of two very small pieces trailing the comet may provide an explanation for why the comet was recently rediscovered. It is likely Comet Giacobini is usually a faint comet and its current brightness may be caused by fresh ices being exposed after pieces of its surface broke off. Though this sounds dramatic it is likely that very little (less than 1% of the mass) of the main nucleus broke or split off. Splitting comets are uncommon but not very rare, with at least one split comet being observed every year.

Discovery images of the two new pieces can be found at the Cordell-Lorenze Observatory.

Re-Discovery of Long-Lost Comet Giacobini

On the night of Sept. 10 UT, two amateur astronomers from Japan found what was thought to be a new comet. Koichi Itagaki and Hiroshi Kaneda used an 8″ telescope equipped with a CCD camera (CCDs are digital cameras optimized for astronomical observation) to find the 12th magnitude comet near the border of the constellations of Aquarius and Aqulia. Mr. Itagaki is no stranger to discovery having previously found Comet Tago-Honda-Yamamoto in 1968 (though credited with a discovery, the comet does not bear his name because comet names are limited to the first 3 discoverers) and with numerous supernovae to his credit.

Michael Meyer of  Limburg, Germany suggested that the comet was not new but rather the return of a long-lost comet not seen since 1897. On 1896 Sept. 4, Michel Giacobini of Nice, France found Comet P/1896 R2 (Giacobini) the old fashioned way by looking through the eyepiece of a telescope. The comet was observed for 4 months before fading from view. Until last night the comet had been lost for 111 years.

You may be asking why 111 years is such a big deal since there are many long-period comets with orbital periods of hundreds to millions of years. For example, Comet Halley returns once every 76 years. Comet Giacobini, on the other hand, is a short-period comet and orbits the Sun every 6-7 years. In fact, the comet has orbited the Sun 17 times since 1896.

Why has this comet stayed hidden for so long? With a brightness of 11th magnitude in 1896 and 12th magnitude in 2008, Comet Giacobini is rather bright. No, it is not bright enough to see without a telescope and it is still too faint to see in the eyepiece of all but the largest backyard telescopes, but in the modern age of telescopes equipped with digital CCD cameras, this comet is an easy target.

Most likely the comet was brighter than usual in 1896 and the same may be true now. Comet outbursts happen from time to time and can be quite spectacular as we saw last year with the brightening of Comet Holmes to easy naked eye visibility. A comet that may be similar to Comet Giacobini is Comet Metcalf-Brewington which was originally seen in 1906 but lost until an outburst in 1991.

The new official name of Comet Giacobini is P/2008 R6 (Giacobini). The “P” means it has an orbital period shorter than 50 years. “2008″ is the year of discovery, or re-discovery in this case. The ‘R’ means it was found during the first half of September and the ‘6′ means it is the 6th comet either discovered or recovered in the 1st half of September. Recovery, and technically the observations of Giacobini are a recovery, is when a comet is observed at a second close approach to the Sun. When comets are observed at two returns they are numbered. This comet will probably be numbered as 205P/Giacobini meaning it is the 205th comet observed at 2 or more returns.

Comet Giacobini currently orbits the Sun once every 6.7 years. It comes as close as 1.53 AU to the Sun (similar to the distance of Mars from the Sun) and travels as far as 5.55 AU from the Sun (slightly beyond the orbit of Jupiter). It is most likely at its brightest and will fade over the next few months.

Image of Comet Giacobini by Gustavo Muler can be found here.

Just Added: Image by  Juan A. Henriquez can be found here.

- Carl Hergenrother