Starship Asterisk*

Chris Peterson wrote:

Ann wrote:It does seem to me that the tail of (this) Comet Lovejoy is relatively faint.

Ion trails are always faint. It's rare for the ion trail to even be visible to the eye. Dust trails are what get bright, and we don't see much dust with this comet. So the apparent brightness of this tail comes down to imaging technique more than anything else.

(I easily saw the comet with image intensified binoculars a few nights ago. But even with that, no tail was visible.)

Ann wrote:It does seem to me that the tail of (this) Comet Lovejoy is relatively faint.

geckzilla wrote:Even a dark comet surface is bright compared to the total blackness of empty space, though. Also, for those two images you posted, you must keep in mind exposure times and magnification. The first one is likely a widefield film exposure of a comet from many years ago. The second looks more like either a fake comet or perhaps it is a telescopic view of the coma. Edit: Actually they could easily both be fake/illustrations. Either way, imaging method and processing matters a lot.

Chris Peterson wrote:

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.

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?

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.

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.

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.

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.

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. :?

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.

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.

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.

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

Joe Stieber wrote:

Chris Peterson wrote: ... the field is ... south up ...

The field is actually north up

Chris Peterson wrote: ... the field is ... south up ...