Comet McNaught now very bright
Published on Jan 14, 2007 at 2:32 pm.
8 Comments.
Filed under comets, skywatching.
Reports are that Comet McNaught has continued to brighten, and it is now very, very bright. In fact, there are reports that it can be seen in daylight, if you have good clear skies and know where to look. I’ll say more on that later.
Daylight comets are not unprecidented, but they are quite rare. I’d love to see this one, but at the moment I am in the middle of an ice storm, and it is cloudy. 
When I first posted about the comet, it was looking like it would be pretty bright, but I definitely didn’t expect it to be this bright. Even my update is now outdated! It is passing only 0.17 AU from the Sun, so that tends to make comets bright. Comets are made of frozen gasses and ice mixed with dust and rock. Close to the Sun, the ices (water ice as well as frozen gasses) sublimates, and blows off into space, producing a bright blue tail. Dust is blown out, too, producing a yellow tail. Both tails point outward away from the Sun, but the dust tail tends to curve a bit. Often on the way in, you see the blue tail, and the dust tail becomes more prominent the closer that you get to the Sun. The gas tail, also called an ion tail, is technically called the Type I tail. It appears bluish because CO+ , a common ion in the tail, scatters blue light more effectively than other colors (much in the way that gasses in our atmosphere scatter blue light more effectively, making the sky blue). The dust tail, technically the Type II tail, reflects sunlight. But, all this material thrown off has to be accelerated away from the nucleus of the comet. Before that happens, it forms a cloud surrounding the little solid chunk of frozen material that is the nucleus. This cloud is the coma, or head of the comet.
The closer that the comet is to the Sun, the warmer its surface gets, and the more material is thrown off. The more that is thrown off, the more that there is to scatter light, so the brighter the comet would be, both the coma and the tail. But, that isn’t the only reason the comet is so bright. Being close to the Sun, there is more light to scatter. Light intensity falls off as the square of the distance, so being half as close to the Sun means having four times the light intensity. Being one tenth as close to Sun makes the sunlight 100 times as intense. Combining both effects makes comets pretty bright at close approaches to the Sun. But exactly how bright depends strongly upon the structure of the comet, its size, and its composition. No two of these things seem to be alike. Other comets have gotten this close to the Sun, or even closer, without becoming this bright. So, this comet, C/2006 P1, or Comet McNaught as it is commonly called, is particularly bright. You can rest assured that it is getting lots of study, and we’ll have some ideas why it is so unusual pretty soon! I’ll probably be posting occasional things about this comet for the rest of the year, long after it is gone from naked eye visibility.
But, for whatever reason, C/2006 P1 (Comet McNaught) is now the brightest comet in decades. Unfortunately, as often happens, the comet is brightest while closest to the Sun. Normally, that means that you can’t see it. But this one is so bright that it is visible in daylight! Now some things, such as Venus, can be readily seen in daylight if you know where to look. The latest magnitude estimates make this comet two to three times brighter than Venus. As I said in earlier posts, that is an integrated magnitude, so it is the total brightness, and it is spread out over the comet. Still, as bright as it is, it should be visible if you look just right.
So, how do you find it in the daylight? Well, you need an easy reference. Fortunately, it is near the Sun, and that is pretty easy to find in the sky! The comet is currently just a bit eastward of the Sun. So, the best way to find it is to block the Sun somehow. Stand in eastern side of the shadow of a building or overhang, with the Sun just barely blocked. This means doing this after local noon — so early afternoon until late afternoon. With the Sun just barely blocked, the comet should appear as a small oblong smudge of light. It might look sort of like light reflecting off of an airplane, except that it isn’t moving across the sky. (Actually, it is moving about a quarter degree west per minute, but that is due to Earth’s rotation.) If you look near mid day, depending upon your latitude, you’ll see something like this:
If you are looking later in the afternoon, depending upon your latitude, it may look something like this:
Now, this works in clear skies. If you have lots of haze, the forget it. You won’t be able to pick out the comet. Often, what most people call “clear” isn’t clear to astronomers. But, if the sky is deep blue color, then you should be OK. If there is a lot of moisture in the air, then there will be a large white disk around the Sun, called the aureole. The bigger and brighter the aureole, the harder it will be to see the comet.
What yoiu are seeing will be mostly the head of the comet. The tail will be harder to pick out in the daylight sky. Reportedly, looking at the comet with binoculars shows the tail. However, do not look with binoculars unless you know exactly what you are doing! If you accidently look at the Sun, then you can damage your eyes, perhaps permanently. So, to avoid that danger, I would suggest that you don’t even try it. It is too easy to lean over a bit and catch the Sun in your binoculars. It is better to miss the comet than to lose your eyesight.
I really wish that I could see this comet with the rest of you, but it was cloudy all week that I was as the AAS Meeting, and it’s been cloudy since I returned home. In fact, we’re having an ice storm today here. The only time that I got to see the comet was on the airplane flying home. If anyone manages to spot the comet in the daylight, I’d like to hear about it!
-Astroprof
Astroprof’s Page » Update on Comet McNaught on January 14, 2007 at 5:34 pm: 1
[…] Note: I have an update to the Comet McNaught update here. -Astroprof […]
Astronomy Buff - Astronomy from a skewed perspective on January 15, 2007 at 2:11 pm: 2
[…] AstroProf on how to observe Comet McNaught. […]
Booberfish Blog » Blog Archive » Comet McNaught on January 15, 2007 at 2:12 pm: 3
[…] Naked eye comets are rare enough as it is, but this month Comet McNaught has been making headlines around the world. In this picture, from Nasa’s Astronomy Pic of the Day, it can be clearly seen above the city of Krakow, Poland, just after sunset. Now there’s word (eg. from Phil Plait and Astroprof) that the comet is so bright that it’s visible in broad daylight. […]
A Ler…-- Rastos de Luz on January 15, 2007 at 5:21 pm: 4
[…] “Comet McNaught from STEREO“, no Tom’s Astronomy Blog. O cometa do momento visto pelo STEREO, um dos mais recentes satélites de observação solar. Ainda sobre este tema, “Comet McNaught now very brightly“, no Astroprof’s Page. […]
Dave Welch on January 16, 2007 at 3:54 am: 5
fantastic visibility looking west from Christchurch New Zealand just after sunset this evening (16th January) - body and tail clearly visible in the red of the sunset. Far larger than any star, very distinctive. This is with the naked eye from the roof of our house.
Paul MacKay on February 3, 2007 at 2:30 am: 6
Im in New Zealand and was so totally blown away by the red glow and the sweeping tail that seemed to go on forever, I drove straight past my destination and got lost. The taial arched across the sky for hours and the comet was still very birght the next night. I thing I watched it for around three or four nights. Does anybody know its dimensions and speed?
Wong on July 11, 2007 at 9:42 am: 7
I saw the Comet Mcnaught when i was in Cromwell,Central Otago New Zealand.I slept few days in my car beside the Dunstant Lake and the comet was just in front of my view.Body and it’s long tail clearly visible and it’s like hanging on the sky.Awesome indeed!!
Astroprof’s Page » Comet Holmes is suddenly news (after 2 weeks) on November 6, 2007 at 12:28 am: 8
[…] Wow. Back on October 24, almost two weeks ago, I heard about the sudden outburst of Comet 17P/Holmes. I wrote about it hours after observing it. There was quite a bit of news about the comet around the internet. Just over a week ago, I posted a photograph of the constellation Perseus, with the comet marked. This has turned out to be one of the brightest comets in a long time, second only to Comet McNaught early in the year. Comet Holmes was clearly visible to the naked eye. Now, as it expands, it is getting harder to see, as I explained recently. And, in all those nearly two weeks, the comet has been virtually ignored by the news media. I saw a brief mention in USA Today, but that was all until Sunday when an amateur astronomer associated with a planetarium in the area wrote about it in the monthly column for the local paper. Then, I see this today. Yeah, they are sure on top of things. […]