Will PANSTARRS really pan out?

Mar

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Comets are a wonderful thing for both amateur and professional astronomers to observe. For amateurs, they are often unexpected visitors, forcing us to hunt a bit more than usual to find their exact location on any given night. And their unpredictability means that some, like Comet Holmes, can brighten up by hundreds, thousands or millions of time, suddenly making them into superstars (supercomets?).

Arguably the best comet to visit Earth (in the northern hemisphere) since Comet Garradd graced our skies in 2011, Comet PANSTARRS C2011 L4 promises to put on a light show. But as I see it, there's a problem. A light show done during the day isn't nearly as spectacular as one done at night, when the sky is darker, and the lights appear more impressive to our eyes. And as I was putting together some charts last night for others to follow this comet, I came to a realization:

This comet may be overhyped.

Don't get me wrong - there's been plenty of caveats. "Low on the western horizon" and "difficult to spot" are phrases used. No, what bothers me are the graphics. I've seen Mercury low in the western sky. I have a nearly flat western horizon near my house. I've even seen Mercury naked-eye as low as 5 degrees off the horizon - which is a pretty remarkable feat, given the glow of twilight still lingering and Mercury's magnitude (similar to that of the comet). And I helped observers see 8th magnitude Comet Hergenrother back in October of 2012.

So what bothers me is two fold:

Comets are not point-sources of light like planets are; they're like nebula and galaxies, with their light spread out over a larger area of sky. This means a "1st magnitude" comet will look dimmer than a planet / star of similar brightness. Seeing objects in the glow of twilight is challenging, and 'naked eye' during daylight hours is not nearly as exciting - or easy! - as naked eye at night.

Why do I say this? Imagine a regular flashlight. Clicked on during the day in sunlight - or even, well, twilight - it doesn't seem to do much. Yes, you can see it, but it's nothing impressive. In darker conditions, it appears much brighter though, yes? Well, Venus can be seen naked eye during the day, if you know where to look. And Venus is point-source, and usually somewhere around magnitude -4. That's 100x brighter than this comet is supposed to be, and the comet isn't point source. And something else: The utter lack of pictures of this comet from the southern hemisphere. If it's so stunning and bright, where are all the photos from Google? Why aren't the astro-media sites splashing photos of it with their stories? (EDIT: Twitter is an amazing thing - I checked my Twitter feed immediately after posting this, and saw a tweet with this PANSTARRS picture. Another one of PANSTARRS here. So there are decent pictures - but I still think there's reason to remain cautious, as you can see the twilight in the photos, and some dim stars in each picture, which demonstrates what the camera can pick up - but the human eye? Not so much.)

Are you starting to see my hesitance about this object? (Post continues below photo)

Comet Hale-Bopp, 1997

Please don't misunderstand me. For experienced observers, and those of us used to seeing objects low on the horizon, this will indeed be a fantastic opportunity, provided we have the good horizon and clear skies to see it. But many of the graphics accompanying the stories show a nice, bright comet with a much longer tail than has been observed (some graphics indicating a 10 degrees-long tail!). Observations have indicated a tail of about 1 degree.

Do you see my frustration?

I remember Comets Hyakutake and Hale Bopp. Hyakutate was the best comet in a couple decades, and it was followed by Hale Bopp which truly was a jaw-dropping, "Holy cow look at that!" type of object. PANSTARRS L4 is not on par with that. And it will be in a difficult area of the sky to see. And comets are notoriously difficult to predict. But unless this comet unexpectedly brightens to magnitude - 5 or -10 (or more), it may not be much to write home about. Yes, observers like me will find it exciting, and do our best to capture images of it to share. And those who have a passing interest in astronomy may find it worth hunting, should their horizon and skies be advantageous.

But don't expect a Hale-Bopp.

What I think will be better, for most of us, is when this comet has risen to 10 degrees (here's how to measure distance in the sky) above the horizon about an hour after sunset - which occurs in late March / early April. Of course, it also will have dimmed to magnitude 4 (or less) by that time, but I'll take a 60x dimmer object on a dark sky background than a brighter one on a background of twilight.

Wouldn't you? Let me know your thoughts in the comments.

Then again, when I took that picture above of Hale-Bopp in 1997, consumer digital photography and retail-level Photoshop were just a dream. So we may get some amazing photos after all. I hope I'm pleasantly surprised. For now, here's where we can expect it to be on March 10 at 30 minutes past sunset, at least it's "best moment in darkness / altitude above the horizon". As for how it actually looks, we'll just have to wait and see: