APOD: This Comet Lovejoy (2014 Dec 25)

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APOD: This Comet Lovejoy (2014 Dec 25)

Post by APOD Robot » Thu Dec 25, 2014 5:07 am

Image This Comet Lovejoy

Explanation: Comet Lovejoy, C/2014 Q2, is framed like a cosmic Christmas tree with starry decorations in this colorful telescopic portrait, snapped on December 16th. Its lovely coma is tinted green by diatomic C2 gas fluorescing in sunlight. Discovered in August of this year, this Comet Lovejoy is currently sweeping north through the constellation Columba, heading for Lepus south of Orion and bright enough to offer good binocular views. Not its first time through the inner Solar System, this Comet Lovejoy will pass closest to planet Earth on January 7, while its perihelion (closest point to the Sun) will be on January 30. Of course, planet Earth's own 2015 perihelion passage is scheduled for January 4. A long period comet, this Comet Lovejoy should return again ... in about 8,000 years.

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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by geckzilla » Thu Dec 25, 2014 5:14 am

Is the deliberately repetitive use of "this Comet Lovejoy" a literary reference of some sort?
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Boomer12k » Thu Dec 25, 2014 5:19 am

Hmmmm.....might try to get a view Monday...supposed to be clear....we will see... :D

Wishing our APOD friends a Merry ONE!!!!
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Chris Peterson » Thu Dec 25, 2014 5:40 am

geckzilla wrote:Is the deliberately repetitive use of "this Comet Lovejoy" a literary reference of some sort?
Terry Lovejoy has discovered five comets: C/2007 E2, C/2007 K5, C/2011 W3, C/2013 R1, and this Comet Lovejoy, C/2014 Q2.
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by geckzilla » Thu Dec 25, 2014 6:01 am

Chris Peterson wrote:
geckzilla wrote:Is the deliberately repetitive use of "this Comet Lovejoy" a literary reference of some sort?
Terry Lovejoy has discovered five comets: C/2007 E2, C/2007 K5, C/2011 W3, C/2013 R1, and this Comet Lovejoy, C/2014 Q2.
Nod. I was curious if there was more to it than that. Perhaps it's just an editor being creative.
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Ann » Thu Dec 25, 2014 7:35 am

As always, I note the colors.

The coma is very green. That is to be expected, although I think it looks a tad greener than usual. Or not. :wink:

The tail is thin and mostly gray, with hints of both blue and green. I might have expected the tail to be bluer.

Is it possible to find out exactly what stars are seen in the background? That would help assess the color of the comet.

By the way, Terry Lovejoy has an irresistible last name. No wonder that those who write about notable comets much prefer to call this comet Lovejoy rather than C/2014 Q2.

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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Chris Peterson » Thu Dec 25, 2014 3:14 pm

Ann wrote:The tail is thin and mostly gray, with hints of both blue and green. I might have expected the tail to be bluer.
It is quite blue on my monitor.
Is it possible to find out exactly what stars are seen in the background?
From astrometry.net, the image center is 100.430°, -39.214°, the field is about one degree on a side and about south up, the image scale is 2.48 arcsec/pixel.
lj_astrometry.jpg
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Ron-Astro Pharmacist » Thu Dec 25, 2014 4:47 pm

Quite a Peach! And there are green “stars” in the sky. With all the other colors there too – I got what I wanted for Christmas!! Though not for me alone – it is very much appreciated.
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Joe Stieber » Thu Dec 25, 2014 7:11 pm

Chris Peterson wrote: ... the field is ... south up ...
The field is actually north up since the tail points more-or-less opposite the sun. Also, east is to the left, so it's a normal view, like one would see in binoculars if the tail was bright enough. Based on the comet's position matched in SkyTools, it was taken around 1200 UT.

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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by geckzilla » Thu Dec 25, 2014 8:10 pm

Joe Stieber wrote:
Chris Peterson wrote: ... the field is ... south up ...
The field is actually north up
I concur. It's north up.
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Ann » Thu Dec 25, 2014 8:29 pm

Chris Peterson wrote:
Ann wrote:The tail is thin and mostly gray, with hints of both blue and green. I might have expected the tail to be bluer.
It is quite blue on my monitor.
Is it possible to find out exactly what stars are seen in the background?
From astrometry.net, the image center is 100.430°, -39.214°, the field is about one degree on a side and about south up, the image scale is 2.48 arcsec/pixel.
lj_astrometry.jpg
Thanks a lot, Chris! :D

The bluest-looking star in the picture is HD 48726. Its apparent B-V index is -0.02, which makes it a bit bluer than Vega. (Vega's B-V index is usually given as either 0.00 or -0.01.) The apparent color of HD 48726 is not nearly as blue as some O- and early B-type stars, however.

Since HD 48726 looks much bluer than the tail of Comet Lovejoy, even though it's just a bit bluer than Vega, I take it that the tail of this comet is not as blue as the (apparent) color of Vega.

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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Chris Peterson » Thu Dec 25, 2014 9:01 pm

Joe Stieber wrote:
Chris Peterson wrote: ... the field is ... south up ...
The field is actually north up since the tail points more-or-less opposite the sun. Also, east is to the left, so it's a normal view, like one would see in binoculars if the tail was bright enough. Based on the comet's position matched in SkyTools, it was taken around 1200 UT.
Yes, it looks that way. Astrometry.net reports "up is 177 degrees E of N", which I'd take as south up. They must be using some funky definition of rotation. When I solve the image using Pinpoint, the rotation angle is +357, or 3° from north. Based on the comet position on the solved plate, I got a time of UT 11:00. And then I noticed that the image has the time shown at the upper left- UT 11:19. Ain't science grand.
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Chris Peterson » Thu Dec 25, 2014 9:04 pm

Ann wrote:The bluest-looking star in the picture is HD 48726. Its apparent B-V index is -0.02, which makes it a bit bluer than Vega. (Vega's B-V index is usually given as either 0.00 or -0.01.) The apparent color of HD 48726 is not nearly as blue as some O- and early B-type stars, however.
The problem is, we don't see color as B-V indexes. It is very difficult to compare color (as a physiological phenomenon) to any instrumental color value. Because the tail is dim, we will see it as a completely different color from a star, even if it has the identical spectrum of that star. So I think the stellar comparison here is of limited value.
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Ann » Fri Dec 26, 2014 6:13 am

Chris Peterson wrote:
Ann wrote:The bluest-looking star in the picture is HD 48726. Its apparent B-V index is -0.02, which makes it a bit bluer than Vega. (Vega's B-V index is usually given as either 0.00 or -0.01.) The apparent color of HD 48726 is not nearly as blue as some O- and early B-type stars, however.
The problem is, we don't see color as B-V indexes. It is very difficult to compare color (as a physiological phenomenon) to any instrumental color value. Because the tail is dim, we will see it as a completely different color from a star, even if it has the identical spectrum of that star. So I think the stellar comparison here is of limited value.
Perhaps not, but in The Color Atlas of Galaxies James D Wray often tried to include foreground stars in his galaxy pictures. He did so in order to compare the B-V and U-B indexes of the star with the B-V and U-B indexes of the galaxy.

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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by DavidLeodis » Fri Dec 26, 2014 12:15 pm

I've just seen this APOD and (like geckzilla) I immediately wondered why its title and explanation referred to "this Comet Lovejoy" as if "this" one had some particular significance. It would have helped if the explanation had a direct link to information about Terry Lovejoy, as it would then become clearer in that he has discovered 5 comets so "this" is just one of those. :?

In the bottom right of the image it mentions SED, but the links in the explanation seemed to have no information about SED. From information that I have now found it may be the Space Exploration Network, but I'm unsure.

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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by geckzilla » Fri Dec 26, 2014 2:48 pm

"This" has special significance in object-oriented programming as a way of identifying the object currently being worked with. Could be related. Or I could be putting far too much thought into this.
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by DavidLeodis » Fri Dec 26, 2014 2:57 pm

To add to my confusion I've only just realised that the time on the image appears to be 11:19 UTC. My understanding is that a 24-hour clock notation should be used for UTC and so 11:19 UTC would be daylight. I wonder therefore if the time should state 23:19 UTC. :?

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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Chris Peterson » Fri Dec 26, 2014 3:12 pm

DavidLeodis wrote:To add to my confusion I've only just realised that the time on the image appears to be 11:19 UTC. My understanding is that a 24-hour clock notation should be used for UTC and so 11:19 UTC would be daylight. I wonder therefore if the time should state 23:19 UTC. :?
No, the image time is certainly close to UT 11:19, or the comet would not be in the position we observe in this image. What I conclude is that Damian did not make this image from England. But that leaves half the world where it's dark at UT 11:19. Including some places here in the U.S. that offer remote telescope access.
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Chris Peterson » Fri Dec 26, 2014 3:18 pm

Ann wrote:
Chris Peterson wrote:The problem is, we don't see color as B-V indexes. It is very difficult to compare color (as a physiological phenomenon) to any instrumental color value. Because the tail is dim, we will see it as a completely different color from a star, even if it has the identical spectrum of that star. So I think the stellar comparison here is of limited value.
Perhaps not, but in The Color Atlas of Galaxies James D Wray often tried to include foreground stars in his galaxy pictures. He did so in order to compare the B-V and U-B indexes of the star with the B-V and U-B indexes of the galaxy.
Yes, but galaxies are made out of stars. Both represent thermal continuum sources. Comparing them instrumentally certainly makes sense, and even visually they are typically similar. But you are comparing the visual appearance of stars with objects that are emitting light in specific narrow wavelength bands. The concept of B-V means nothing for the latter, and the response of our eyes is completely different for the two things.
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Ron-Astro Pharmacist » Fri Dec 26, 2014 3:20 pm

geckzilla wrote:"This" has special significance in object-oriented programming as a way of identifying the object currently being worked with. Could be related. Or I could be putting far too much thought into this.
Or "This" Love Joy was a cleaver tie-in to the
Lovejoy.jpg
of the season. Hopefully for this type we won't be waiting 8,000 years all the people on Earth to see.
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by dlw » Fri Dec 26, 2014 6:13 pm

On a slightly different aspect of this beautiful image, I note that there are "streaks" in the tail appearing to emanate from the coma. I assume these are "thin" areas with less effluent. So, now that we know more about what the core of a comet might look like, do these streaks indicate something interesting about the core of this comet?

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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by DavidLeodis » Fri Dec 26, 2014 6:26 pm

Chris Peterson wrote:
DavidLeodis wrote:To add to my confusion I've only just realised that the time on the image appears to be 11:19 UTC. My understanding is that a 24-hour clock notation should be used for UTC and so 11:19 UTC would be daylight. I wonder therefore if the time should state 23:19 UTC. :?
No, the image time is certainly close to UT 11:19, or the comet would not be in the position we observe in this image. What I conclude is that Damian did not make this image from England. But that leaves half the world where it's dark at UT 11:19. Including some places here in the U.S. that offer remote telescope access.
Thanks Chris for your help. :)

I had assumed that the time stated was the local time where the image was taken, which I assumed was at Damian's main location at his home in England. When I realised that it would though be daylight I thought it might be at the site he uses in Barbados, but that is only 4 hours behind UTC so it would be light there. I had though not thought about remotely obtaining images, which could therefore be in an area still dark at 11:19 UTC.

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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Chris Peterson » Fri Dec 26, 2014 6:31 pm

DavidLeodis wrote:I had assumed that the time stated was the local time where the image was taken, which I assumed was at Damian's main location at his home in England. When I realised that it would though be daylight I thought it might be at the site he uses in Barbados, but that is only 4 hours behind UTC so it would be light there. I had though not thought about remotely obtaining images, which could therefore be in an area still dark at 11:19 UTC.
If his webpage is up-to-date, the equipment used isn't equipment he owns. But it is typical of the sort of setup remotely operated observatories utilize.
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Ron-Astro Pharmacist » Fri Jan 02, 2015 4:47 pm

This comet's nucleus seems unusually bright as I look through images of other comets. Any idea why some comets have bright comas and some have bright nuclei? In most of the Comet Lovejoy photos I've seen the coma is a pretty big and diffuse and, what I think is the nucleus, is small and bright. I would suppose it would be from their individual constituents "..its lovely coma is tinted green by diatomic C2 gas fluorescing.." but perhaps it is from angle arriving into the inner solar system, its size or shape or proximity to the sun or multiple other variables??

I hope this topic will rise again when another well-discussed comet closes in and rounds the sun. That ought to be interesting when seen close-up. 8-)
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Re: APOD: This Comet Lovejoy (2014 Dec 25)

Post by Chris Peterson » Fri Jan 02, 2015 4:52 pm

Ron-Astro Pharmacist wrote:This comet's nucleus seems unusually bright as I look through images of other comets. Any idea why some comets have bright comas and some have bright nuclei?
You can't see the nucleus of this comet- or of any active comet. All you are seeing is coma and tail. The nature of the outgassing and dust ejection determines the radial density profile of the coma.
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