Starship Asterisk*

Comet Lovejoy with M44

Explanation: While anxiously waiting for Comet ISON to brighten further as it falls toward the Sun, northern skygazers can also find three other bright comets in the east before dawn. In fact, Comet Lovejoy C/2013 R1 is currently the morning sky's brightest. Only discovered in September and not a sungrazing comet, this Comet Lovejoy is nearing the edge of naked-eye visibility and might be spotted from very dark sky sites. Sporting a greenish coma and tail in this telescopic view taken on November 7, Comet Lovejoy is about 0.5 AU from our fair planet and 1.2 AU from the Sun. The comet is having a photogenic Messier moment, sweeping past well known star cluster M44, the Beehive in Cancer. Yellowish bright star Delta Cancri is near the bottom of the frame.

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I presume the diffraction spikes were added for artistic effect. It seems incongruent that all of the stars have tracking motion but the diffraction spikes are clear and crisp. Anyway, cool picture. The astronomy community seems in the midst of a fever pitch for comets lately and still growing with the approach of ISON. Even if it turns out to be a stinker it's the adventure leading up to the moment that counts, right?

Lovely photo (and nice photo-bombing M44). There are a few comets visible from Southern skies, too, at the moment, including this one. (G'day Mr Lovejoy.)

Objective Question: Can we see in this photo, either of the Sun-like stars in M44, around which the recently discovered planets Pr0201b and Pr0211b orbit?

Subjective Question: Diffraction spikes -- do they add to or detract from images like this, and in which ways? (Written before I saw geckzilla's comment [and I didn't even notice the tracking motion.])

Tracking motion or ...something. I'm not sure what to call it. It could also just be short star trails. For some reason I was thinking the comet was being tracked but I guess that's not necessary. Whatever, the thread gets its daily dose of ignorance early today.

Nitpicker wrote: Objective Question: Can we see in this photo, either of the Sun-like stars in M44, around which the recently discovered planets Pr0201b and Pr0211b orbit?

The location of the stars with planets can be seen here. I didn't try to spot them in today's APOD, but it should be possible to see them. The orientation of both photos is the same.

Ann

AWESOME!!!!!!!!!!!!!!!

As the world's foremost authority on Comets....that is my professional opinion.....LOLOLOL!!!!!!!!!

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Thanks, ANN!!!!! For showing that....fascinating...


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Thanks Ann. I had a feeling they would be visible.

And geckzilla, I may be using the jargon incorrectly, but in this context, is there a difference between the meaning of tracking motion and star trails? I say this as an expert on the generation of tracking errors.

geckzilla wrote:I presume the diffraction spikes were added for artistic effect. It seems incongruent that all of the stars have tracking motion but the diffraction spikes are clear and crisp. Anyway, cool picture. The astronomy community seems in the midst of a fever pitch for comets lately and still growing with the approach of ISON. Even if it turns out to be a stinker it's the adventure leading up to the moment that counts, right?

I really hate fake diffraction spikes that are added with software, what's the point? They always happen to look fake and I prefer the real thing caused by telescope and camera optics. Still doesn't change the fact that it is an awesome photo!!

starsurfer wrote:

geckzilla wrote:
I presume the diffraction spikes were added for artistic effect. It seems incongruent that all of the stars have tracking motion but the diffraction spikes are clear and crisp. Anyway, cool picture.

I really hate fake diffraction spikes that are added with software, what's the point? They always happen to look fake and I prefer the real thing caused by telescope and camera optics. Still doesn't change the fact that it is an awesome photo!!

Damian Peach is out there alone in the middle of the night on top of some godforsaken mountain top trying to produce to the finest astro-photographs for you and you falsely accuse him of adding diffraction spikes with software! For shame

http://www.damianpeach.com/observatory.htm wrote:
<<The second site which I visit regularly is the Caribbean island of Barbados, located at 13°06N, 59°30W. This location is superb, and at this low latitude the Planets are always high in the sky. Also, the site benefits from a laminar flow off the ocean, delivering a high percentage of nights of excellent seeing conditions. It also delivers a high percentage of clear/partly clear nights being the sunniest island in the Caribbean, and a very comfortable night time low of ~77°F. It is the finest site I have ever observed from at/near sea level.>>

geckzilla wrote:I presume the diffraction spikes were added for artistic effect. It seems incongruent that all of the stars have tracking motion but the diffraction spikes are clear and crisp.

I sensed something incongruous about the tracking artifacts/star trails of the dimmer stars vs. the brightest stars, and you just pinpointed it.

Nitpicker wrote:Subjective Question: Diffraction spikes -- do they add to or detract from images like this, and in which ways?

Practically, I think they help boost the prominence of the brightest stars in a medium with insufficient dynamic range to record their true brightness.

Aesthetically, I think they enhance the beauty of the photos, but only with an appropriate level of subtlety. Subtlety is the key. (Diffraction spikes in computer art usually look jarringly fake, and ruin otherwise good renders.)

Edit: The image of Taurus in my avatar was computer-generated from BSC4 data.

As for me, one of these days I'm going to have to start looking up the meanings of these big astronomical terms words like 'incongruous'. Yep, one of these days. But not today.

"incongruous" isn't an astronomical term.

Ok, I'll just scratch the term "astronomical term", and replace it with the word "words".

owlice wrote:
"incongruous" isn't an astronomical term.

It's a math term:

Incongruous numbers (Arith.): two numbers, which, with respect to a third, are such that their difference can not be divided by it without a remainder, the two numbers being said to be incongruous with respect to the third.

"The constitution vests the power of declaring war incongruous." - George Washington

geckzilla wrote:I presume the diffraction spikes were added for artistic effect. It seems incongruent that all of the stars have tracking motion but the diffraction spikes are clear and crisp.

I don't think the diffraction spikes are artificial. The telescope Damian uses has a spider-mounted secondary, so diffraction spikes are normal. I didn't find any technical information for this image, but based on other images I assume around a 15-minute total exposure time. That corresponds to about 90 arcseconds of drift of the comet against the background stars, or about 6 pixels when looking at the full-sized image. That's more than the slight elongation seen in the stars (which I guess is what you are calling "tracking motion").

My guess is that the tracking was on the stars, and the slight elongation is an artifact of the stacking method used to try and minimize trailing for both the stars and comet at the same time (which isn't something that can be done perfectly). Perhaps Damian can chip in here with some more technical information about the exposure and processing.

It looks like it could be a single exposure tracking on the comet, which would mean a one shot color camera.

stephen63 wrote:It looks like it could be a single exposure tracking on the comet, which would mean a one shot color camera. :?:

Looking at Damian's other comet pictures, I'm betting on the monochrome 6303 camera with a stack of several minute long luminance exposures and a short RGB sequence. If this was a single image tracking on the comet there would be star trails longer than the slight elongation we see here.

Chris Peterson wrote:

stephen63 wrote:It looks like it could be a single exposure tracking on the comet, which would mean a one shot color camera.

Looking at Damian's other comet pictures, I'm betting on the monochrome 6303 camera with a stack of several minute long luminance exposures and a short RGB sequence. If this was a single image tracking on the comet there would be star trails longer than the slight elongation we see here.

I was curious about the horizontal banding in the upper right. I thought stacking would have eliminated it, but who knows the method of stacking.
Edit: maybe not.

Chris Peterson wrote:Perhaps Damian can chip in here with some more technical information about the exposure and processing.

Hopefully. It's fun to try to do some forensic work and determine these things for fun but eventually I just want to know.

stephen63 wrote:I was curious about the horizontal banding in the upper right. I thought stacking would have eliminated it, but who knows the method of stacking.
Edit: maybe not.

I think this is actually an artifact of the stacking itself. Depending on the total duration of the exposure (as opposed to the total exposure time), the spacing isn't unreasonable for drift between the comet and the stars. One way to stack images like this is to align on the comet and use a median-type combine to get the comet without any stars, and then separately align on the stars, producing a clean background with a slightly smeared comet, then use some type of layer masking to combine the two. Definitely the sort of process that can lead to artifacts, especially at the image edges.

The big question (the “incongruity”) is why the diffraction spikes are not smeared to the extent that the stars are elongated. Damian, please help us out!

Cousin Ricky wrote:The big question (the “incongruity”) is why the diffraction spikes are not smeared to the extent that the stars are elongated. Damian, please help us out!

It isn't clear to me that they aren't. Since the diffraction spikes are at 45° to the direction of elongation, we'd expect the broadening to be the same for both axes, meaning there is no simple way to detect it.

That said, the saturated (or nearly saturated) stars that show diffraction spikes might be slightly less elongated, suggesting a masking technique that resulted in fewer of them being stacked- not an unreasonable thing to do.

Chris Peterson wrote:

Cousin Ricky wrote:The big question (the “incongruity”) is why the diffraction spikes are not smeared to the extent that the stars are elongated. Damian, please help us out!

It isn't clear to me that they aren't. Since the diffraction spikes are at 45° to the direction of elongation, we'd expect the broadening to be the same for both axes, meaning there is no simple way to detect it.

That said, the saturated (or nearly saturated) stars that show diffraction spikes might be slightly less elongated, suggesting a masking technique that resulted in fewer of them being stacked- not an unreasonable thing to do.

I appreciate all the comments on the diffraction spikes. I have learnt a few things. (I hadn't even considered that they might have been added after the fact [or not]. Quite a foreign concept to me.) All I did know was that they are unavoidable with certain telescope constructions, based on the kind of mounting of the secondary mirror or diagonal, or similar. I tend to find diffraction spikes distracting, in much the same way that sparkly dresses worn by beautiful women can be distracting. But maybe that is the point. Still, I'm more interested in the stars (and the women) than the sparkles.

Edit: I realise that any unresolvable point source of light can only ever be observed as a diffraction pattern. But are some patterns better (or more natural) than others?