When observing a comet, what we see is the outer coma; the dust and vapor outgassing from the nucleus as it gets heated from the Sun.
So I decided to take one of my photos taken with my Skywatcher 80ED telescope (600mm focal length) and see if I could process the image to spot where the nucleus is located.
This can be achieved by using the MODULO command in IRIS and viewing the result in false color. The results are better if you do a logarithmic stretch of the image before the MODULO command. It took some trial-and-error to get the right parameters, but the end results isn’t so bad.
For the fun of it I tried to see if I could calculate the size of the comet nucleus using the image. At the most narrow the nucleus on the photo spans 5 pixels. Based on a previous plate-solve result I know that my setup (Canon 80D and Skywatcher 80ED telescope) results in scale of 1.278 pixels per arc-second. Then I used Stellarium to get the Earth-coment distance on July 23rd (103.278 M km)
When I plugged in all the numbers I get a comet nucleus size of approximately 2000 km, which to me seamed a little on the BIG size.
I live in a heavily light polluted city, therefore unless it’s bright, I won’t see it. But boy was I ever happy with the outcome of this comet! In my books C/2020 F3 (NEOWISE) falls in the “Great Comet” category, and it’s by far the most photographed comet in history because it was visible for so long to folks on both sides of the globe.
My last encounter with a bright comet was in 2007 with periodic 17P/Holmes when it brightened by a factor half a million in 42 hours with this spectacular outburst to become visible to the naked eye. It was the largest outburst ever observed with the corona becoming temporarily the biggest visible object in the solar system. Even bigger than the Sun!.
So when the community was feverishly sharing pictures of the “NEOWISE” I had to try my luck; I wasn’t about to miss out on this chance of a lifetime.
I have to say that my first attempt was a complete failure. Reading up when it was the best time to try to photograph this comet most indicated one hour before sunrise was the right time. So I checked on Google Maps where I could setup for an un-obstructed view of the eastern horizon (my house was no good) and in the early morning with my gear ready at 4am I set off. To my disappointment and the “get-back-to-bed-you-idiot” voice in me, it didn’t work out. By the time I got to the spot and had the camera ready, the sky was already too bright. No comet in sight, and try as I might with the DSRL, nothing.
Two evenings later and another cloudless overnight sky I decided to try again, but this time I would make it happen by setting the alarm one hour earlier: 3am. That is all that it took! I was able to set-up before the sky could brighten, and then CLICK! I had this great comet recorded on my Canon SD memory card.
I didn’t need any specialized gear. All it took was a DSLR, a lens set to manual focus, a tripod and 5 seconds of exposure and there was the comet. I snapped a bunch of frames at different settings and then headed back home to catch the last hour of sleep before starting another day of work. Lying in bed I felt like I had accomplished something important.
As the comet swung around our Sun and flipped from a dawn to a dusk object I decided I should try to photograph it once again, but this time with the Skywatcher 80ED telescope. At that point, the comet was dimming so every day that passed would be more difficult. It was only visible in the North-West horizon at sunset, which meant setting up in the front the the house, fully exposed to street lights. Not ideal, but I had nothing to loose trying.
I used our tree in the front yard to act as a screen and was able to locate and photograph this great comet. Polar alignment wasn’t easy, and when I had the comet finally centered and focused with the camera, overhead power lines were in the field of view. I decided to wait out 30 minutes and let the sky rotate to the lines out of the view. Besides, it will get darker anyways which should help which the photo. But I also realized that my “window” of opportunity was small before houses would start obscuring the view as the comet would dip to a lower angle with the horizon.
I’m sure in the years to come people will debate if this was a “Great Comet”, but it my books it’s definitely one to remember. It cemented with me the concept that comets are chucks of “dirty ice” that swing around the sun. Flipping from a dawn to dusk observable object after a pass around the Sun is a great demonstration of the elliptical nature of objects moving in our solar system.
Back in March, the astronomy crowd was buzzing about a possible”naked-eye” comet expected in late May 2020. Comet C/2019 Y4 (ATLAS) was first detected at the tail end of December as a very dim magnitude 19.6 object and by mid-March it had brighten to an easy telescope target magnitude of 8. Those not familiar with the magnitude scale, going from 19.6 to 8 is not a doubling in brightness, but around a 4000 times increase!
That dramatic increase in brightness help fuel the hype for the Great Comet of 2020, and there were two other factors that got people excited:
It would be visible at dusk from the Norther Hemisphere, hence within easy viewing to much of the world population.
It was following a similar orbital path as the “Great Comet of 1843“, suggesting that it was from the same original body and could potentially provide the same viewing spectacle. That 1843 comet was visible in daytime!
Well all that went south when the comet’s breakup was observed in late March after peaking momentarily at magnitude 7. It began to dim, along with any hopes of a Great Comet repeat. Below is a graph showing the the original (grey line) and revised (red) comet brightness forecast (dots being observed measurements) on this chart created by Seiichi Yoshida (firstname.lastname@example.org)
Comet C/2019 Y4 (ATLAS) Brightness – Copyright(C) Seiichi Yoshida
Comet C/2019 Y4 is expected to make its closest approach to the sun on May 31st, however most experts believe it will disappear (disintegrate) before that date. Seeing that I had a small window of opportunity to capture the comet I decided to try my luck last Saturday evening.
Below is an extremely processed (and ugly) image that I got by combining 25 photos (15 seconds each at ISO 3200) using my Skywatcher 80ED scope. The photo just about makes out the distinctive blue-green hue and elongated shape of a comet. It is around magnitude 10, very diffuse and about 147 million km away from us the day this photo was taken.
Comet C/2019 Y4 (ATLAS) on April 18, 2020 – Very faint at about magnitude 10. Imaged with 80ED telescope 25 x 15sec
I pushed the image processing so hard that I was able to pick up faint magnitude 13 galaxies!
On to the next comet!
Telescope: Skywatcher 80ED
Camera: Canon 80D
Image: 25 x 15sec at ISO3200 (6 minutes)
The word “planet” comes from the Greek work “planan” which means to wander. Early star gazers noticed that some bright stars moved with respect to other fixed stars. Those bright stars are our closest planets: Mercury, Venus, Mars, Jupiter and Saturn. Comets also move a fair bit across the sky, but the origin of the word has more to do about stars “with long hair” than it’s traveling behavior.
Last weekend I managed to photograph comet 41P//Tuttle–Giacobini–Kresák, and I identified in my blog that it’s movement was visible frame to frame. Well I’ve finally gotten around to create a small animation of that movement. For those wondering what’s the comet’s velocity, it’s currently travelling at 37.4 km/s.
Animation of comet 41P/Tuttle–Giacobini–Kresák (41 minutes)
The above is composed of 32 frames, each a 1 minute exposure spanning a time of 41 minutes. You are probably thinking “it should be 32 minutes, not 41!”. That is because I have a delay between each frame to allow the camera to send the photo to the computer. Hence between the first and last frame, 41 minutes have elapsed.
Periodic comet 41P/Tuttle-Giacobini-Kresak is currently a magnitude 8 object for telescopes and unlike many other current bright comets like C/2015 ER61 (PANSTARRS) and C/2017 E4 (Lovejoy) it is visible for a good portion of the night while the other two are only visible in the morning twilight for those like me in the northern hemisphere.
On April 13th comet 41P was in the constellation Drago, which is where I managed to photograph it.
Not much of a tail on this comet, and I’ve checked other photos taken with larger scopes and the result is also just a coma around the nucleus.
Because it is passing near Earth, its movement in the sky is quite noticeable frame-to-frame in the captured images. For the registration and stacking with comets, this is done by alignment on the comet and not the stars, hence the star trails in the above image. I performed another stacking, this time using the stars to align, and the comet’s movement becomes obvious. The displacement measures 2.6 arc-minutes in the 41 minutes that elapsed between first to last exposure.
My setup was less than ideal, as the constellation was only visible from the front of my house. Yes that is a lovely street-light shining right across the street. Luckily the telescope was pointing a little to the right, and a rolled piece of cardboard help act as an dew-shield extension to block the glare. But on the good side I had a nice solid concrete surface and got a very good polar alignment with 1 minutes exposures giving me nice round stars. Hmmm, might explore this setup a little more often…
Setup in the garage to image comet in constellation Drago
Camera: Canon XTi (450D)
Exposure: 32 x 60sec ISO 800
DeepSkyStacker, IRIS, GIMP
If you are able to get out of bed early and the sky is clear, equipped with binoculars you should be able to catch a fast-moving comet as it swings by Earth at about 32 lunar distances over the next few days. The best time is just prior to sunrise as the comet will be higher in the sky in the East. Use Jupiter as well as bright stars Vega and Arcturus to get your bearings. With each day the comet will rise earlier and will appear higher in the sky as the chart below shows; comet position at 5am for the next week. However it will diminish in brightness as it moves away from Earth on after February 11th.
Comet 45P over the next few days starting Feb 10th.
This isn’t the closest a recording of a comet passing near Earth, but it does make it to the 8th spot since modern observation and have been keeping track of near Earth objects (1950). Back in August 15 2011, it happen to pass even closer, only 23 lunar distances, making it also the 5th closest comet approach.
With a storm system moving up the eastern edge US and Canada, my chances of getting any clear morning sky is pretty slim…
It wasn’t easy but on Friday the weather cooperated and I was able to capture a glimpse of comet 45P/Honda-Mrkos-Pajdusakova. That’s if you consider -10°C outside temperature to set-up a telescope and operate a laptop cooperation from Mother Nature.
In my previous post I gave myself a 2-day challenge to capture this comet as it was essentially the last few days at a decent magnitude 7 brightness before becoming non-observable as it swings around the sun over the coming weeks. And when it returns to the northern latitude sky in mid-to-late February it will be dimer at magnitude 10. In the image below, I labeled some of the brighter stars with their visual magnitude as reported by the Tycho-2 catalog.
Comet 45P/Honda-Mrkos-Pajdusakova – around magnitude 7 on January 6th, 2017
I had a very small window of about 30 minutes to make any observation and photograph it. The challenge started with setting up without polar alignment; the sky was still too bright to locate Polaris, and instead relied on the position of Venus to align the mount. As it was still twilight, I was limited to short exposures to keep the histogram on the left half on the camera and to make out a star from the background sky. I actually started at ISO 400 with only 1 second exposure while adjusting the focus around Theta Cap (magnitude 4). And as the minutes ticked by I was able to slowly increase my exposure as the twilight darkness permitted. With neighboring trees, and rooftops coming into view I had to grab as many frames as possible. In the end I got 14 images with 6 seconds exposure at ISO 800 before calling it quits.
With such short exposures no chance of capturing any comet tail, but the green halo is unmistakable comet.
My challenge for the next two days (Clear Sky Chart is predicting clear skies) is to observe and capture comet 45P/Honda-Mrkos-Pajdusakova. It should be relatively easy to locate by hopping from Venus then down the bright stars of Capricorn starting with Delta, Gamma, Iota and ending with Theta. Then half a degree to the left of Theta Cap is magnitude 6 star HD201057. Comet 45P at magnitude 7 should be just next to that star.
The challenge will be its position low near the horizon, I may have obstructions before it sets. And the twilight may not be dark enough for a magnitude 7 object. The viewing time window will be quite small…wait for darkness and it will fall out of view.
Location of comet for January 5th 5:30pm EST
No need for telescope, it’s also a binocular object.
45P is the 45th periodic comet (Halley being the 1st identified periodic comet) with a 5.3 year period. Its orbit swings from just past Jupiter to in between Mercury and Venus.
C/2016 U1 ( NEOWISE )
Currently observable at magnitude 9 and predicted to brighten to magnitude 7 in mid January. Discovered on October 21, 2016. Not visible in the southern hemisphere.
C/2015 V2 ( Johnson )
Faint at magnitude 12, and will continue to brighten until mid 2017, with good chances of observation.
C/2015 ER61 ( PanSTARRS )
Should brighten to magnitude 7 spring of 2017, unfortunately not very visible to the northern latitudes. However it will cross many NGC and Messier objects throughout the first half of the year.
Expected to brighten to magnitude 6-7 around at the start of March, overall visible for about 45 days. For those in the northern hemisphere, best observations will be the end of February.
After over 12 years Rosetta will be decommissioned by sending it down to impact with comet 67P/C-G. This fate was decided as the comet is moving away from the sun, beyond the orbit of Jupiter and the solar panels will not generate enough power to keep the spacecraft operational. Even “hibernation” is not a possibility as heaters are still required to keep the critical systems idling. Hence mission control will send commands in the next few days such that on September 29th a series of maneuvers will send it on a impact trajectory with the comet. As the comet’s gravity is rather weak (1/10,000 of Earth’s) it will most likely not be a fatal impact. However the Rosetta will be instructed to shutdown upon contact with the surface in order not to “pollute” the deep space communication network with spurious and uncommanded signals. This is expected to happen on September 30th 10:40 GMT.
So where is comet 67P/C-G? Travelling towards the orbit of Jupiter, in constellation Virgo, opposite to the sun from Earth’s perspective. Normally an event like this would be timed to be observable at night from Earth such that telescopes can gather scientific data. But at apparent magnitude 20 (to compare, Pluto has a mean apparent magnitude of 15) it will be very difficult to observe. And the impact is not expected to generate a large plume of dust. Therefore it will be up to Rosetta to record and beam back to Earth as much data during the descent before shutting down for good.
Rosetta and comet 67P/C-G position on September 30th
Welcome to a journey into our Universe with Dr Dave, amateur astronomer and astrophotographer for over 40 years. Astro-imaging, image processing, space science, solar astronomy and public outreach are some of the stops in this journey!