Catching the Comet

Comet C/2020 F3 (NEOWISE) from Fourmilab, Switzerland, 2020-07-18 21_15 UTC

Click to enlarge

Tonight, the evening of 2020-07-18, around 21:00 UTC, I finally got the chance to observe and photograph comet C/2020 F3 (NEOWISE), the Great Comet of 2020, on the first night of (kinda) clear sky after the comet appeared in the evening sky.  Even though the sky was visibly milky, with thin haze reflecting distant lights, after becoming dark adapted, the comet was an easy naked-eye object near the northwestern horizon (which is elevated due to the Jura mountains in that direction).  Through binoculars (Canon 15×50mm image stabilised) the star-like nucleus and coma were well-defined, and the dust tail extended until it was lost in the murky sky.  I was unable to pick up the dimmer, straight, blue ion tail either with the unaided eye or binoculars.

To photograph the comet, I set up my Leica M240 rangefinder digital camera with the Leica Noctilux 50 mm f/0.95 lens on a tripod.  This is a very fast “normal” lens, which means it provides a field of view comparable to the human eye, but its light capturing capability far exceeds that of the eye.  The picture you see here is comparable to what you’d see looking directly at the comet, if your eye were much more sensitive than a camera made of meat can possibly be.

I made a variety of exposures using ISO speeds between 400 and 3200 and exposure times ranging from 1 to 8 seconds (the maximum available on the M240), with automatic subtraction of a dark frame for noise reduction.  The picture I chose to show here was taken at ISO 800 with an exposure time of 6 seconds at F/0.95.  Leica lenses have a Teutonically-precise stop at the infinity focus setting, so for astrophotography there’s no fiddling with focus: you just turn it to the infinity stop and the image is perfect.  For a lens with such an insane focal ratio, the Noctilux performs remarkably well off-axis, but I have cropped the image to elide some slightly potato-shaped stars in the corners of the full frame (which contains no useful information in any case).

It is clear from stretching the image into less aesthetic presentations that the comet’s tails extend well beyond what is captured here.  In a darker, clearer sky with a longer exposure, the comet would be even more spectacular.  In this picture, you can see the ion tail extending straight to the left of the broad, curved dust tail.  It doesn’t jump out at you, but it’s clearly there, especially when you click the picture to view the enlargement.  The ion tail, made of gas emitted by the comet, energised by solar radiation, and entrained by the solar wind, is blue, but the hue isn’t apparent in this picture: it’s just a greyish, maybe slightly blue, straight ray.

For observers in the northern hemisphere, this apparition is a superb chance to glimpse a magnificent comet which is easy to find, observe, and photograph.  I remember when my father pointed out comet Arend-Roland (C/1956 R1) when I was a little kid.  If you have small children, now’s your chance to get them to look away from their screens for a moment and up to the glories of the heavens.  It may change their lives, and those of their children and descendants.

If you observe the comet, please describe what you saw and, if you get any photos, post them in the comments.

Here is a NASA guide to spotting the comet in the coming days.  If you miss the comet on its current swing around the Sun, it’ll be back in around 6800 years.

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Author: John Walker

Founder of Ratburger.org, Autodesk, Inc., and Marinchip Systems. Author of The Hacker's Diet. Creator of www.fourmilab.ch.

21 thoughts on “Catching the Comet”

  1. In this picture, the nucleus of the comet appears near the the 3.14 magnitude star Iota Ursae Majoris, which has nothing to do with the comet, being 47.3 light-years from the Sun.  Since the comet is currently 107.21 million km from Earth, or 357.6 light-seconds from Earth, this is a picture with great depth of field—and everything (except the foreground) is in focus!

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  2. For comparison, here are images from some earlier comets I’ve observed.  The technology of photographing dim, extended objects has changed greatly over the years, and is reflected in these photos.

    The first comet I photographed was Halley’s comet from Australia in 1986, but the photos, taken on film, were just of a fuzzy blob which I’ve never bothered to digitise.

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  3. Here is the same picture as in the main post, but contrast stretched to show the true colour of the sky, which, around 20 minutes before the end of astronomical twilight, had a residual very dark blue colour.  This tended to mask the ion (gas) tail, which is intrinsically blue.  I have labeled the ion and dust tails.

    C/2020 F3 (NEOWISE): ion and dust tails

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  4. Since it was a rare clear night near Pittsburgh, I thought about going out for a look. Compared to meteor showers, which always seem to have the best viewing after midnight, this comet is more inviting. However, I cannot get a view of sky near the horizon from anywhere in my yard. The western PA terrain is made of many small hills and valleys. I often tell people that here, one is always looking at the side of a hill – like my backyard – with tall trees to further obliterate a view of the horizon; to see part of the sky, one must look up near vertically.

    I find my mood is affected by my surroundings and there is something about the perspective of being able to see the horizon which is esthetically pleasing. Not seeing it, all the time, has the opposite effect. That is why I love my trips to Switzerland. There are an abundance of places with wide vistas. On some mountain tops accessible by cable cars, on a clear day one can see mountains more than 75 miles distant. In any case, if there is another clear night during the comet viewing period, I will march down the street where the horizon is slightly less occluded. The comet, according to the link, will also be appearing higher in the sky each succeeding night. Maybe I can catch a glimpse with my spotting scope, which is portable. I have an old Meade Schmidt-Cassagrain 6 inch telescope, but it is so bulky and heavy it is difficult to carry. As well, it only tracks deep space objects or objects like planets in the ecliptic.

    All of which is yet another way of saying – I wish I had followed my instincts and done whatever was necessary to move to Switzerland when I was younger. I, myself and my wife could probably qualify for permanent residence since my adult son is Swiss (they allow family unification), born and bred. However, I would have to abandon my other 2 children and grandchildren in what we all used to think of as ‘the land of the free’.

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  5. civil westman:
    The comet, according to the link, will also be appearing higher in the sky each succeeding night. Maybe I can catch a glimpse with my spotting scope, which is portable. I have an old Meade Schmidt-Cassegrain 6 inch telescope, but it is so bulky and heavy it is difficult to carry. As well, it only tracks deep space objects or objects like planets in the ecliptic.

    Yes, each night the comet will be higher in the sky and set later, which gives you more time after the end of astronomical twilight before it sets.  The comet is expected to dim over time, but slowly, and this will be compensated for by being higher in the sky and suffering less from atmospheric extinction and light pollution.  Later in the month the Moon will interfere with the darkness of the sky.

    The drive on your Meade telescope should work fine for observing or photographing the comet.  The comet does move with respect to the distant stars, but sufficiently slowly that a photographic exposure, whose time is limited by sky glow and light pollution, is unlikely to be blurred.

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  6. Yes, the comet is clearly visible as far south as the American South West — where perhaps clear skies and limited light pollution compensate for it being closer to the horizon.

    In days gone by, the appearance of a comet was taken as a sign that Bad Things were going to happen — wars, pestilence, and the deaths of kings.  This year, we have most of those covered already;  maybe the message of the comet is that things can always get worse.

    So let’s enjoy the show while it lasts.  This too shall pass.

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  7. Canon 60D, f/4, 5 sec, ISO 3200, taken 7/15.  Owing to light pollution, the comet was not visible by the naked eye, and I had to guess at both location and focus (having a non-Teutonic lens).

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  8. I noticed a bright triangular-shaped object in the upper right hand corner of the original picture at the top of the post. It is even more clear  in the ‘click to enlarge’ image. Any ideas? It’s the shape of an F-117. I know, Switzerland doesn’t have any and they are black and non-reflective.

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  9. civil westman:
    I noticed a bright triangular-shaped object in the upper right hand corner of the original picture at the top of the post. It is even more clear  in the ‘click to enlarge’ image. Any ideas? It’s the shape of an F-117. I know, Switzerland doesn’t have any and they are black and non-reflective.

    It’s a bright star, distorted by the off-axis performance of the Noctilux.  There are compromises in achieving its phenomenal light capturing ability and sharpness around the optical axis, and this is one of them.  Almost all of these distortions go away if you stop it down to f/2 or smaller, but then that negates the whole purpose of this lens.

    At least it wasn’t one of these.

    Ovni: "Chad"

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  10. Here’s my best shot from tonight.  This is, I believe, the best photo of a comet I’ve ever taken.

    Comet C/2020 F3 (NEOWISE) from Fourmilab, 2020-07-19 22:45 UTC

    Today wasn’t promising, as there was cloud cover and haze for most of the day, but in the evening things improved and after the end of astronomical twilight (21:50 UTC today) I decided to give it a try.  The sky was less than completely transparent, but even though the comet was closer to the apparent horizon (elevated because I’m looking at a ridge of the Jura), the comet popped out more clearly than it did last night when, its being lower in the sky, I had to observe earlier before it set.

    I used the same photographic gear described in the main post.  This shot, taken around 22:45 UTC, clearly shows the ion/gas tail to the left and the dust tail curling to the right and gives a hint of their complete extent, which you still can’t see in this picture.  For the first time, I was (barely) able to pick up the ion tail in binoculars, but I was still unable to see or photographically capture its blue emission colour.  Click the image to enlarge.

    Every night, the comet will appear higher in the sky for observers in the northern hemisphere, meaning, until the Moon begins to interfere later in the month, we’ll get better opportunities to see it in darker skies with less extinction by the atmosphere.

    Please continue to post your observations and photos in the comments.

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  11. Inspired by your pictures and by the linked NASA guidance, I went to the west-facing beach at sunset. It was a spectacular sunset, briefly turning a swath of sky and sea solid orange in a way I never saw before. But it was mostly cloudy to the northwest, my husband’s back was killing him, and I realized the wait for actual darkness was too long. So we gave up and came home. I studied the area below the Big Dipper for a while from my backyard but couldn’t see a thing, either because of light pollution(all my neighbors hate the darkness it seems) or because I could not see low enough. Still, a lovely evening.

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  12. I have no new comet pictures for today.  Around 22:30 UTC  I went out and was immediately able to spot the comet, but it was veiled by thin clouds which blurred the nucleus and obscured the extent of the tail.  I decided to use the opportunity to test the gear I intended to try to capture the head of the comet in more detail.  This was my three decades old Nikon 300 mm f/4.5 lens on a Nikon D600 digital camera.  I wanted to see how easy it would be to find the head of the comet in the frame and what scale I could expect for the image of the nucleus, coma, and inner tail.

    I was able to find and frame the head of the comet and take a number of pictures which indicated that, had the sky co-operated, I might have gotten some usable pictures, but with the atmospheric gunk through which I was shooting tonight, all detail was obscured.

    I’ll try it again if and when I get a clear sky.

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  13. Today, 2020-07-24, was not promising, including a brief thunderstorm, off and on drizzle, and thick clouds, but, as sometimes happens as temperatures fall after sunset (which was at 21:14 local time today) the skies began to clear and by the end of astronomical twilight (23:38 CEST) there was some gunk but the northwestern sky was mostly unobscured.

    The comet is beginning to dim, and so was not as obvious to the naked eye (although this may have been due to a less transparent sky), but was easily picked up in binoculars.  I decided to have a go at my project of imaging the comet’s nucleus, coma, and innermost tail, so I set up my Nikon D600 camera and more than three decades old Nikon 300 mm f/4.5 manual focus lens, which has served me so well in solar and lunar eclipse photography.  This lens, like many pre-autofocus (“out-of-focus”) lenses, has a hard mechanical stop at infinity, so there’s no fiddling when focusing on celestial objects.

    It did take more than a little bit of fiddling to get the comet in the frame.  With a focal ratio of f/4.5, a dim object like the comet was completely invisible in the viewfinder, and Live View did not have the sensitivity to pick it up, so it was a matter of “by guess and by gosh” homing in until the comet appeared in the preview frame on long exposures.

    The goal here is not an artistic presentation, but digging a bit of science out of ugly images captured with a modest camera and lens from an unguided tripod.  Once I framed the comet and adjusted the exposure, I took a series of shots with different exposure times at ISO 3200 and 6400.  All were taken at the lens’s maximum aperture of f/4.5.  The lens performs reasonably well at this aperture, and with such a dim subject, you need every photon you can get.

    Choosing the most promising image, which was shot at ISO 3200 with a sufficiently short exposure time to avoid obvious star trails, I flattened the colours to monochrome to eliminate rampant colour noise and produced this image of the comet’s head.  Note that, compared to the images of the comet and its extended tail you’ve seen in earlier photos in this post, here you’re looking just at the bright dot at the bottom of the comet and the very beginning of its tail.  You can click the image to enlarge, but you won’t see much more in the enlargement.

    C/2020 F3 (NEOWISE) nucleus, coma, and inner tail, 2020-07-24

    The problem in imaging comets is the enormous dynamic range in brightness between the starlike nucleus and the dim extended tail.  The human eye, which responds logarithmically to light, does a fine job of this, but film and digital sensors which record light intensity linearly cannot capture all of the phenomenon.  Here, I have set the exposure so that the inner tail, which is very bright in pictures of the extended comet, is barely visible, and yet the head of the comet—its coma and nucleus—is still hopelessly overexposed.  There is an intriguing “bump” protruding from the head at around the 7 o’clock position: more about this later.

    Now, let’s process this same image in colour with a different intensity transfer function: one which applies a logarithmic transform to the flux recorded by the camera’s sensor.

    C/2020 F3 (NEOWISE): inner coma and nucleus, 2020-07-24

    Now we can see inside what was a white blown-out blob in the image above.  The coma, composed of dust and gas emitted recently from the nucleus, is clearly defined, and shows up as blue-green due to emission of gases emitted by solar radiation.  Here is a Forbes article explaining the cause of the colours of comets’ comas and nuclei.

    The blue-green is due to emission by carbon monoxide (CO), cyanogen (CN), and diatomic carbon (C₂) stimulated by solar ultraviolet radiation.  There is still a large intensity range in this image, which cannot be shown on the screen.  The innermost part of the head of the comet, next to the nucleus, is much brighter than its surroundings, and that is lost here.  The innermost tail, by comparison, composed mostly of dust reflecting sunlight, is red by comparison, and in this stretched image appears ruddy.

    The “bump” we saw in the first monochrome image appears to be a jet erupting from the nucleus of the comet, ejecting dust and gases which light up the head in its direction.  I’m pretty sure this is a genuine effect and not the result of some photographic artefact because it showed up in all of the photos I took around this time.  These jets, emitting streams of dust and gas as the nucleus rotates, produce the exquisitely detailed fine structure in the comet’s tail as they stream away into space.

    Recall, the Roaring Twenties are not just about a pandemic disease loosed on the world by an incompetent communist slave state, ignoramuses tearing down monuments to people whose names they’ve never heard before, suppression of the God-given human rights of free speech, free assembly, and self-defence, but they’re also a time of wonder: when modest amateur equipment in a backyard can produce images of a celestial phenomenon which would have made professional astronomers gasp with astonishment when I was a kid.

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  14. John Walker:
    Recall, the Roaring Twenties are not just about a pandemic disease loosed on the world by an incompetent communist slave state, ignoramuses tearing down monuments to people whose names they’ve never heard before, suppression of the God-given human rights of free speech, free assembly, and self-defence, but they’re also a time of wonder: when modest amateur equipment in a backyard can produce images of a celestial phenomenon which would have made professional astronomers gasp with astonishment when I was a kid.

    As wonderful as some technological advances have been, the lasting and memorable effects of this decade may well be the (continuing) decline of Western civilization and the ascendancy of more oppressive regimes, both at home and abroad. In the worst case, the recent events may be the harbinger of a new Dark Age. If so, I’m grateful for having lived during a civilizational peak.

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  15. Farewell, fine comet!

    NEOWISE from Switzerland: 2020-07-27

    This is probably the last photo I will post of C/2020 F3 (NEOWISE) on this apparition.  With each successive night, the comet is receding from the Earth and Sun and dimming, and the waxing Moon increasingly interferes with observation until after the comet has set.  This picture was taken at 22:02 UTC on 2020-07-27 from my driveway at Fourmilab.  The sky was slightly hazy with a few thin clouds, brightened by first quarter Moon, reddened as it approached the horizon.  The exposure was ISO 6400 for 13 seconds at f/3.5 with a Nikon zoom lens at 28 mm focal length on a Nikon D600 camera.  I hand focused at infinity, and may have been a tad off.  In any case, the light from the Moon washed out any fine detail.  The comet is clearly visible, with the head showing its characteristic blue colour and the inner tail visible: everything else is lost in the haze and moonlight.  As happens more and more with long exposures at night, the image was corrupted by a satellite trail—thank you Elon!  (Of the photos I took tonight, of which this is the best, fully a third showed satellite trails, with two of them showing a pair in separate orbits.)

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