Year of the Comets

Thus far, the 21^st century has been an underwhelming one for comets. The few comets that have been visible on Earth were dimmer than predicted, or not even visible to naked eye observers. With a little luck, 2013 could be the year comet-watching changes for the better.

During 2013, we will have not one, but two comets potentially visible to the naked eye. The first is Comet PANSTARRS (formal designation C/2011 L4) which should reach its maximum brightness during the next few weeks (around March 9). The second bright comet of 2013 will be Comet ISON (formal designation C/2012 S1) — ISON is anticipated to achieve its maximum brightness around Thanksgiving (possibly appearing even brighter than the full Moon). Comet ISON is expected to be the brighter and more spectacular of these two comets, but since it won’t be be making an appearance for another six months, this article focuses on Comet PANSTARRS.1

Comet PANSTARRS is named after the Pan-STARRS2 imaging system — developed at the University of Hawaii’s Institute for Astronomy — which was used to discover the comet back in 2011. Compared to most comets, Comet PANSTARRS was discovered while it was still very far away, nearly 8 AU3 (about 744 million miles, or 1.2 billion km) from the Sun. When a comet is that far from the Sun, it reflects very little sunlight, which means it is extremely difficult to detect.

Unfortunately there is disappointing news. Comet PANSTARRS originally had been predicted to reach a maximum magnitude4 (brightness) of ‑1.0 (easily visible with the naked eye), but based on the most recent observations from the southern hemisphere, the comet’s brightness is well below what had been predicted.

Seiichi Yoshida, editor of Weekly Information about Bright Comets, has downgraded his predictions for Comet PANSTARRS’ maximum magnitude to a mere +3.0. (On the magnitude scale, lower numbers are brighter than higher numbers, so a magnitude of +3.0 is significantly dimmer than the magnitude ‑1.0 originally predicted.) Other comet experts are updating their magnitude predictions as well, but there is little agreement among them. Revised magnitude predictions range from +1.8 to as low as +4.0. The Viewing Chart at the end of this article contains Yoshida’s revised magnitude predictions.

Even though Comet PANSTARRS may deliver a dimmer-than-expected performance, it will still be a sight worth seeing — it’s just that you may need to pull out a pair of binoculars (or a small telescope). The Viewing Chart at the end of this article also provides coordinates to locate Comet PANSTARRS during the coming months.

Predicting the brightness of comets is an inexact science (to put it politely), so things could still change. But as of right now, it looks like the first comet of 2013 may turn out to be an underperformer. The good news is that according to the most current predictions, when Comet ISON makes its appearance later this year, it should be 10,000 times as bright as Comet PANSTARRS.

Comet PANSTARRS Brightness and Location

Date	Original Predicted Magnitude	Revised Predicted Magnitude	Right Ascension (2000.0)	Declination (2000.0)
Feb. 21	+2.0	+4.0	22h10m	-39°15′
Feb. 26	+1.0	NA	22h59m	-32°42′
Mar. 2	+0.5	NA	23h34m	-25°15′
Mar. 3	+0.0	NA	23h42m	-23°06′
Mar. 5	-0.5	+4.0	23h56m	-18°27′
Mar. 9	-1.0	+3.0	0h18m	-8°11′
Mar. 15	-0.5	+4.0	0h33m	7°11′
Mar. 17	+0.0	NA	0h35m	11°43′
Mar. 22	+1.0	NA	0h35m	21°32′
Mar. 27	+2.0	NA	0h34m	29°38′
Apr. 2	+3.0	+5.5	0h31m	37°50′
Apr. 9	+4.0	NA	0h28m	46°03′
Apr. 19	+5.0	NA	0h22m	56°18′
Apr. 30	+6.0	+7.0	0h13m	66°21′
May 6	+7.0	NA	0h00m	72°15′
May 15	+8.0	NA	23h29m	78°30′

How to read this chart:

The Magnitude is the apparent brightness of the comet on that day. A lower magnitude is brighter than a higher magnitude. (So for example, mag. ‑1.0 is brighter than mag. 1.0, and mag. 1.0 is brighter than mag. 4.0)

For comparison:

• Venus (at its brightest): Magnitude = —5.0
• Sirius (brightest star visible in the Northern Hemisphere): Magnitude = —1.0
• The North Star (Polaris): Magnitude = +2.0
• Faintest objects visible in urban sky w/ naked eye: Magnitude = +3 to +4

The Right Ascension and Declination are the comet’s location in the sky. If you are not familiar with locating objects using ascension and declination, you can use the Comet PANSTARRS Finder Charts on FreeStarCharts.com.

1. I’ll publish a similar article for Comet ISON closer to August 2013. [↩]
2. Pan-STARRS is an acronym for Panoramic Survey Telescope and Rapid Response System. [↩]
3. An AU — or Astronomical Unit — is a unit of measure based on the average distance between the Earth and the Sun, or about 93 million miles (150 million km). So an object that is 8 AU from the Sun is 8 times as far from the Sun as Earth is. [↩]
4. The magnitude is the apparent brightness of an object in the sky. NOTE: A lower magnitude is brighter than a higher magnitude. So for example, mag. ‑1.0 is brighter than mag. +1.0, and mag. +1.0 is brighter than mag. +4.0 [↩]