Comet Section        



The Comet Section would like to thank all the observers who have sent us their comet observations. Please keep the observations coming. For those of you who have been observing comets recently and have not submitted them to the Comet Section or to the ALPO Image Archive, please do so. An Image Gallery for the Comet Section has been created and is being populated with images.

At any time, there are usually 1 or more comets within reach of visual observers with small telescopes and a half dozen or more within reach of large telescopes. CCD observers can count on many tens of comets being visible to them. This report will concentrate on a few of the more interesting comets that are currently observable this month.

C/2012 F6 (Lemmon)

The brightest comet of the month is Comet Lemmon. It peaked at magnitude 4.5 when it passed perihelion on March 24 at a distance of 0.73 AU from the Sun. At that time the comet was located deep in the southern sky and wasn’t visible to northern observers. The comet has since moved north and is located in the morning sky against the stars of Andromeda. As the month progresses its northward motion will make it a circumpolar object for much of the Northern Hemisphere.

Observers are currently estimating its brightness around magnitude 7.0 to 7.5. Since the comet is moving away from the Earth and Sun it will fade to magnitude 8.0 to 8.5 by the end of the month. CCD images are still showing the comet to be gas-rich/dust-poor with a gas tail over a degree in length. Large aperture telescope images show not only the tail but also a number of near-nucleus jets.

On June 1 Lemmon is located 1.46 AU from the Sun and 1.75 AU from Earth, by mid-month it is 1.66 AU from the Sun and 1.77 AU from Earth and by the end of the month it will be 1.87 AU from the Sun and 1.83 AU from Earth.


Even though Comet Lemmon holds the rank of brightest comet in the sky, many observers seem to be ignoring it in favor of our second brightest comet, Comet PANSTARRS. This comet passed perihelion back on March 10th of this year at a relatively small perihelion distance of 0.30 AU from the Sun. At that time, it was as bright as magnitude ~+1.5. Though situated deep in the glow of twilight, visual observers were able to detect it with the naked eye and even see ~0.5-1.0 degrees of a tail. CCD imagers caught a more spectacular sight as the tail extended over a large range of position angles and contained a large number of striae.

By the end of May, the comet had faded to magnitude 7.5 to 8.5. What PANSTARRS currently lacks in brightness it more than makes up in tails, or more specifically its anti-tail. On May 26/27, the Earth passed through the plane of PANSTARRS’ orbit resulting in the appearance of a long thin anti-tail. In some images this feature stretches more than 8 degrees from the head of the comet. For examples see the following Comet Section Gallery images here, herehere and here (or just go to the C/2011 L4 folder of the Comet Section Image Gallery). The anti-tail should still be visible during the first half of June but will fade from view as the Earth moves out of the comet’s orbital plane.

The comet is currently a northern circumpolar object and starts the month a few degrees from Polaris. By the end of the month it is located in Draco north of the constellation Bootes. This will probably be the last month for easy observation of PANSTARRS in small telescopes as it should fade to magnitude 10-11 by month’s end. On June 1 it will be 1.84 AU from the Sun and 1.85 AU from Earth. By the end of the month it will be 2.29 AU from the Sun and 2.26 AU from Earth.

C/2012 L2 (LINEAR)

This comet is only visible to southern observers. Now a month past its May 9 perihelion (q=1.50 AU), Comet LINEAR has been reported as bright as magnitude 8.5-9.0. The comet seems to have rapidly brightened in the month or two prior to perihelion. It will be interesting to see if it maintains its current brightness or fades just as quickly as it brightened. Comet Linear’s distance from the Sun will increase from 1.54 to 1.64 AU and its distance from Earth will increase from 2.31 to 2.35 AU.

Inbound Comets

The following comets are inbound and though currently faint, have the potential to be interesting objects over the next few months. We ask that CCD and large telescope visual observers add them to your observing lists. Observations made as objects approach the Sun are very important to not only making predictions of their future brightness but also help researchers understand the processes and chemical species that drive their activity.

C/2012 S1 (ISON)

Dubbed by the press and even NASA PR as the ‘Comet of the Century’, Comet ISON is the most anticipated comet of the year. Some press articles and even a professional paper have predicted that the comet will reach magnitude -16 (brighter than the Full Moon) when it arrives at perihelion on November 28 of this year (Thanksgiving Day!). At that time the comet will only be 1.2 million km above the surface of the Sun (resulting in an apparent elongation of ~0.5 degrees from the Sun).

It is highly unlikely the comet will become that bright. For starters, that prediction assumes the comet will brighten at an ‘average’ rate for a long-period comet. Unfortunately there are two problems with that. All comets, and especially dynamically new comets like ISON, have a habit of not brightening at a steady rate or brightening at a slower than average rate. In the case of the above mentioned Comet PANSTARRS it ceased brightening for a number of months before perihelion. ISON is doing PANSTARRS one better (or worse in this case). Not only has it not brightened since January, it has actually faded intrinsically. As a result the comet which was as bright as magnitude 15 a few months ago is now only at 16th magnitude even though it is closer to the Sun and Earth.

Whether ISON will be a great comet, just a good comet, or completely disintegrate as it rounds the Sun is still to be seen. The first week or two of June mark the last opportunity to observe ISON before it gets too close to the Sun. The comet will once again be visible as a morning object in mid-August. We ask that CCD observers try to image ISON as long as possible before it sinks out of view. The comet starts the month 3.5 AU from the Sun in the constellation of Gemini.


Yet another Pan-STARRS find, C/2012 K1 is still 5.6 AU from the Sun at the start of June. It won’t reach perihelion for over a year (August 27, 2014 at 1.05 AU from the Sun). The comet is currently around 15th magnitude and is situated near the Hercules-Ophiuchus border. At perihelion the comet should be a nice binocular object though that will all depend on how it brightens. CCD images and large telescope visual estimates will allow us to better model this comet’s current and future activity levels.

All ephemerides/positions for the above comets and all other comets can be generated at the Minor Planet Center and JPL/Horizons websites.

- Carl Hergenrother (Comet Section Acting Co-Coordinator)

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