Good Comet... or Great Comet?
July 16, 2020 8:45 PM Subscribe
Comet C/2020 F3 (NEOWISE) is in the neighborhood this month and it's giving the best performance by a comet visible in the Northern Hemisphere since Comet Hale-Bopp in 1997. NEOWISE — named for NASA’s Near-Earth Object Wide-field Infrared Survey Explorer, the telescope which first spotted the comet on March 27th — is certainly a very good comet, though it remains to be seen if it’s what astronomers would call a ‘great comet’. There actually isn’t a settled definition for a 'great comet' aside from it having an exceptional brightness, but astronomers assure us they know one when they see one. So let’s revisit the acknowledged greats of the 21st Century so far before getting into more detail on our current, quite nice visitor.
Given the lack of clear agreement on what makes for a 'great comet', it's hard to say how often you might see one. On average, you can expect a major comet to be visible every 5-10 years. Great comets might be expected only every 20-30 years, but there's been lots of variability across the centuries. Lately your chances for seeing a great comet have been heavily dependent on your location: there's been a recent trend of great comets being visible only from the Southern Hemisphere.
The last comet to claim greatness was Comet C/2011 W3 (Lovejoy) in late 2011, discovered by Australian IT engineer and amateur astronomer Terry Lovejoy, who reported it as “a rapidly moving fuzzy object”. Comet Lovejoy was a special kind of comet, known as a sungrazer. And it did exactly what it says on the tin: it came very, very near to the Sun’s surface, less than 140,000 km / 87,000 mi at perihelion (the point at which a body is closest to the Sun) while moving at an incredible 0.18% the speed of light. This made it one of the fastest objects ever observed in our solar system, a distinction shared only with other sungrazers. Comet Lovejoy was a member of the Kreutz sungrazers, a family of comets sharing similar orbital paths that are believed to be surviving fragments of a larger progenitor comet that broke apart perhaps a couple thousand years ago. Those surviving fragments break apart even more when they return so it’s quite an extended family by now, with over 4000 members discovered so far.
As so often happens with sungrazers, Comet Lovejoy was widely expected to boil away and/or have its nucleus torn apart by tidal forces due to its solar close encounter. Miraculously, it survived its passage through the Sun’s corona and we captured some amazing close-up shots of it narrowly escaping doom. However, Lovejoy did appear to disintegrate a few days after perihelion, perhaps as a delayed effect of the thermal shock.
Because perihelion for sungrazers is so close to the Sun they are often quite bright, and several of them have consequently been deemed ‘great’ comets. Lovejoy was at its brightest just before perihelion, which, unfortunately, meant it was lost in the Sun’s glare from Earth’s point of view. As it began its outbound journey in late December it was finally revealed in its full glory. With some observers describing its appearance like a searchlight, Lovejoy earned the moniker the ‘Great Christmas Comet of 2011’. The spectacle was mainly limited to observers in the Southern Hemisphere.
Our other ‘great comet’ of the recent past, C/2006 P1 (McNaught), is also known as the ‘Great Comet of 2007’. Discovered by Scottish-Australian astronomer Robert H. McNaught (himself known as ‘The World’s Greatest Comet Discoverer’, with at least 82 tally marks etched on his telescope), it’s the brightest comet of the twentieth century so far and the second brightest since 1935. With a maximum apparent magnitude of -5.5 (lower is brighter), Comet McNaught was brighter than Venus (-4.14 mean magnitude), normally the brightest object in the night sky aside from the Moon (-12.74 mean magnitude). McNaught, like Lovejoy, also saved its best show for the Southern Hemisphere. Unlike Lovejoy, McNaught is not a sungrazer. It is significant for being the largest comet observed so far, presenting a barrier to the solar wind that stretched 1.5 times the distance between the Earth and the Sun (or 1.5 au).
NEOWISE, our present candidate for greatness, does not bear the name of an individual discoverer, but rather the tool used to discover it. Like most comets, NEOWISE has two tails. The larger one is greyish white or yellow, made of dust shed from the surface of the comet’s nucleus. The thinner, bluish one is the comet’s ion tail, which is made up of gases that have been ionized by losing electrons in the Sun’s intense light. The divide in the ion tail may mean NEOWISE actually has two ion tails. Ion tails are always pointed straight away from the Sun. Dust tails, while also pointing away from the sun at all times, appear curved due to the comet’s orbital motion. The wide variety of dust particle sizes also results in the dust tail usually being much broader than the ion tail, as the particles receive different amounts of pressure from solar radiation depending on how big they are.
NEOWISE arrived at perihelion on July 3 and is currently on its way out. But before it's gone it'll make a not-very-close pass by Earth (perigee) on July 22. Brightness estimates for NEOWISE had it at about +1.0 earlier this month and around +2.0 right now (anything less than +6.5 is typically considered visible to the naked eye). Forecasts are for continued dimming til it fades away perhaps in August. Despite its decreasing brightness, the increasing size of NEOWISE's dust tail and it's closer proximity to Earth mean it'll be a spectacular—some may say great—sight for the next several days.
Given the lack of clear agreement on what makes for a 'great comet', it's hard to say how often you might see one. On average, you can expect a major comet to be visible every 5-10 years. Great comets might be expected only every 20-30 years, but there's been lots of variability across the centuries. Lately your chances for seeing a great comet have been heavily dependent on your location: there's been a recent trend of great comets being visible only from the Southern Hemisphere.
The last comet to claim greatness was Comet C/2011 W3 (Lovejoy) in late 2011, discovered by Australian IT engineer and amateur astronomer Terry Lovejoy, who reported it as “a rapidly moving fuzzy object”. Comet Lovejoy was a special kind of comet, known as a sungrazer. And it did exactly what it says on the tin: it came very, very near to the Sun’s surface, less than 140,000 km / 87,000 mi at perihelion (the point at which a body is closest to the Sun) while moving at an incredible 0.18% the speed of light. This made it one of the fastest objects ever observed in our solar system, a distinction shared only with other sungrazers. Comet Lovejoy was a member of the Kreutz sungrazers, a family of comets sharing similar orbital paths that are believed to be surviving fragments of a larger progenitor comet that broke apart perhaps a couple thousand years ago. Those surviving fragments break apart even more when they return so it’s quite an extended family by now, with over 4000 members discovered so far.
As so often happens with sungrazers, Comet Lovejoy was widely expected to boil away and/or have its nucleus torn apart by tidal forces due to its solar close encounter. Miraculously, it survived its passage through the Sun’s corona and we captured some amazing close-up shots of it narrowly escaping doom. However, Lovejoy did appear to disintegrate a few days after perihelion, perhaps as a delayed effect of the thermal shock.
Because perihelion for sungrazers is so close to the Sun they are often quite bright, and several of them have consequently been deemed ‘great’ comets. Lovejoy was at its brightest just before perihelion, which, unfortunately, meant it was lost in the Sun’s glare from Earth’s point of view. As it began its outbound journey in late December it was finally revealed in its full glory. With some observers describing its appearance like a searchlight, Lovejoy earned the moniker the ‘Great Christmas Comet of 2011’. The spectacle was mainly limited to observers in the Southern Hemisphere.
Our other ‘great comet’ of the recent past, C/2006 P1 (McNaught), is also known as the ‘Great Comet of 2007’. Discovered by Scottish-Australian astronomer Robert H. McNaught (himself known as ‘The World’s Greatest Comet Discoverer’, with at least 82 tally marks etched on his telescope), it’s the brightest comet of the twentieth century so far and the second brightest since 1935. With a maximum apparent magnitude of -5.5 (lower is brighter), Comet McNaught was brighter than Venus (-4.14 mean magnitude), normally the brightest object in the night sky aside from the Moon (-12.74 mean magnitude). McNaught, like Lovejoy, also saved its best show for the Southern Hemisphere. Unlike Lovejoy, McNaught is not a sungrazer. It is significant for being the largest comet observed so far, presenting a barrier to the solar wind that stretched 1.5 times the distance between the Earth and the Sun (or 1.5 au).
NEOWISE, our present candidate for greatness, does not bear the name of an individual discoverer, but rather the tool used to discover it. Like most comets, NEOWISE has two tails. The larger one is greyish white or yellow, made of dust shed from the surface of the comet’s nucleus. The thinner, bluish one is the comet’s ion tail, which is made up of gases that have been ionized by losing electrons in the Sun’s intense light. The divide in the ion tail may mean NEOWISE actually has two ion tails. Ion tails are always pointed straight away from the Sun. Dust tails, while also pointing away from the sun at all times, appear curved due to the comet’s orbital motion. The wide variety of dust particle sizes also results in the dust tail usually being much broader than the ion tail, as the particles receive different amounts of pressure from solar radiation depending on how big they are.
NEOWISE arrived at perihelion on July 3 and is currently on its way out. But before it's gone it'll make a not-very-close pass by Earth (perigee) on July 22. Brightness estimates for NEOWISE had it at about +1.0 earlier this month and around +2.0 right now (anything less than +6.5 is typically considered visible to the naked eye). Forecasts are for continued dimming til it fades away perhaps in August. Despite its decreasing brightness, the increasing size of NEOWISE's dust tail and it's closer proximity to Earth mean it'll be a spectacular—some may say great—sight for the next several days.
I saw it after sunset last night.
It was spooky because I could only see it in my peripheral vision. It was just a light gray patch of sky when looked at head-on, even though I was in a dark sky area with the Milky Way fully visible. It looked great through binoculars.
The spooky effect makes it clear to me why the ancients considered comets to be bad omens.
posted by monotreme at 9:00 PM on July 16, 2020 [7 favorites]
It was spooky because I could only see it in my peripheral vision. It was just a light gray patch of sky when looked at head-on, even though I was in a dark sky area with the Milky Way fully visible. It looked great through binoculars.
The spooky effect makes it clear to me why the ancients considered comets to be bad omens.
posted by monotreme at 9:00 PM on July 16, 2020 [7 favorites]
I've seen a bunch of nice pictures, but this one over Mont Saint Michel is one of the coolest.
posted by CheeseDigestsAll at 9:31 PM on July 16, 2020 [5 favorites]
posted by CheeseDigestsAll at 9:31 PM on July 16, 2020 [5 favorites]
Saw it tonight as well, roughly the same viewing experience as monotreme. Looked like a smudge at first, maybe a wispy patch of clouds but binoculars really help.
posted by efalk at 11:52 PM on July 16, 2020
posted by efalk at 11:52 PM on July 16, 2020
Of course, my skies became overcast just as the comet arrived.
posted by Thorzdad at 4:27 AM on July 17, 2020
posted by Thorzdad at 4:27 AM on July 17, 2020
Awesome post! :-)
posted by Don.Kinsayder at 4:49 AM on July 17, 2020 [1 favorite]
posted by Don.Kinsayder at 4:49 AM on July 17, 2020 [1 favorite]
My lovely wife and I drove around the city looking for decent viewing vantages last night after dark, but never saw it. We understood it to be not far above the horizon, which is obstructed nearly everywhere in a city. This weekend we may try driving well out of town to try again.
posted by Gelatin at 5:24 AM on July 17, 2020
posted by Gelatin at 5:24 AM on July 17, 2020
there all great comits Edmind
posted by glonous keming at 5:48 AM on July 17, 2020 [8 favorites]
posted by glonous keming at 5:48 AM on July 17, 2020 [8 favorites]
NASA's Astronomy Picture of the Day has a lot of great Comet Neowise photos.
posted by ALeaflikeStructure at 6:21 AM on July 17, 2020
posted by ALeaflikeStructure at 6:21 AM on July 17, 2020
It's totally worth seeing. You really need binoculars though unless you have a very dark sky.
posted by bondcliff at 6:55 AM on July 17, 2020
posted by bondcliff at 6:55 AM on July 17, 2020
This comet is very frustrating as someone who lives in a valley. When it was more of a morning comet, it was behind the big hill to the east. In the evening it's in a sort of "hole" where I can see lower on the horizon, but by the time it's dark enough to see it's below the trees. On top of that, I live in Western PA, which is one of the cloudiest regions of the country. Hopefully I'll be able to see it in binoculars or my scope later in the month when it is higher.
posted by dirigibleman at 7:52 AM on July 17, 2020
posted by dirigibleman at 7:52 AM on July 17, 2020
NEOWISE is pretty easy from suburban or better skies in binoculars. In SW Austin, I could see it in binoculars even though it was very low and through the light pollution of Austin.
The trick is to see it before it's too low but after the skies are pretty dark. It's well below the bowl of the Great Dipper about an hour after sunset. At that point it's a hands width or two above the horizon. About an hour to hour and a half after sunset is okay.
Finding it is probably the hardest part for someone unfamiliar with the sky.
It's a far far cry from Hyakutake and Hale-Bopp though. Hyakutake had an enourmus tail when seen from dark skies. Hale-Bopp was so bright and concentrated enough to be easily visible with tail from cities. Those were great comets for the northern hemisphere.
McNaught was so bright it was easily visible in broad daylight even though it put on it's best show under dark skies for the Southern Hemisphere.
posted by jclarkin at 9:08 AM on July 17, 2020 [1 favorite]
The trick is to see it before it's too low but after the skies are pretty dark. It's well below the bowl of the Great Dipper about an hour after sunset. At that point it's a hands width or two above the horizon. About an hour to hour and a half after sunset is okay.
Finding it is probably the hardest part for someone unfamiliar with the sky.
It's a far far cry from Hyakutake and Hale-Bopp though. Hyakutake had an enourmus tail when seen from dark skies. Hale-Bopp was so bright and concentrated enough to be easily visible with tail from cities. Those were great comets for the northern hemisphere.
McNaught was so bright it was easily visible in broad daylight even though it put on it's best show under dark skies for the Southern Hemisphere.
posted by jclarkin at 9:08 AM on July 17, 2020 [1 favorite]
I've also been seeing Neowise on my starfinder app as way too low on the horizon here which has been disappointing. It's basically blocked by the mountains. I keep hoping it'll creep a few degrees higher so I can actually see it...
posted by feloniousmonk at 9:23 AM on July 17, 2020
posted by feloniousmonk at 9:23 AM on July 17, 2020
My urge to procrastinate has never paid such dividends. I couldn't force myself to get up before dawn, but the first night it was an evening event I tracked it down and got some great shots from my deck.
I'm old enough to remember comet Kahoutek, which was somewhat of a let-down. Neowise, on the other hand, has been a pleasant surprise.
posted by OHenryPacey at 9:49 AM on July 17, 2020 [1 favorite]
I'm old enough to remember comet Kahoutek, which was somewhat of a let-down. Neowise, on the other hand, has been a pleasant surprise.
posted by OHenryPacey at 9:49 AM on July 17, 2020 [1 favorite]
This is indeed a great comet. Best since Hale-Bopp! And that was also a great comet!
Except for the whole UFO cult mass suicide thing.
posted by jquinby at 10:22 AM on July 17, 2020
Except for the whole UFO cult mass suicide thing.
posted by jquinby at 10:22 AM on July 17, 2020
Well, this thing made me drive up into the mountains and hike to the peak through a dark forest in the middle of the night, which was an adventure I'd have never undertaken otherwise, so obviously it's the greatest comet.
posted by dominik at 10:33 AM on July 17, 2020 [7 favorites]
posted by dominik at 10:33 AM on July 17, 2020 [7 favorites]
Hale-Bopp was so amazing. I remember at its height someone telling me that they hadn't taken the time to hunt for it and I was baffled. The subject came up because we were indoors in a brightly-lit room and the comet was clearly visible out the window.
I don't do pre-dawn observing, and it's been cloudy for me since Neowise moved into the evening sky. Good to know that it's an averted-vision object.
posted by fantabulous timewaster at 11:03 AM on July 17, 2020 [1 favorite]
I don't do pre-dawn observing, and it's been cloudy for me since Neowise moved into the evening sky. Good to know that it's an averted-vision object.
posted by fantabulous timewaster at 11:03 AM on July 17, 2020 [1 favorite]
I went to a nearby park last night, which was the best place I could walk to that wasn't obscured by trees. Had a good view of the relevant patch of sky, but couldn't see a thing in it due (I'm presuming) to local light pollution. Like, not even normal stars; nothing at all between the big dipper and the horizon.
If I had been able to get a sense of where the smudge is, I probably would have pulled my telescope to the park, but I didn't have it in me to try and search through the scope. I don't have binoculars.
Thinking about driving out of town some evening; unfortunately it looks like the last couple of nights were really great viewing conditions and now it's going to start being cloudier for a while...
posted by nickmark at 12:48 PM on July 17, 2020
If I had been able to get a sense of where the smudge is, I probably would have pulled my telescope to the park, but I didn't have it in me to try and search through the scope. I don't have binoculars.
Thinking about driving out of town some evening; unfortunately it looks like the last couple of nights were really great viewing conditions and now it's going to start being cloudier for a while...
posted by nickmark at 12:48 PM on July 17, 2020
Also, all these time-lapse and long-exposure photos that make it look like the comet is super bright and easy to find are annoying. Especially when they don't say they're time-lapse. They're pretty pictures, but feels like a bait-and-switch to the general public, y'know?
posted by nickmark at 12:52 PM on July 17, 2020 [1 favorite]
posted by nickmark at 12:52 PM on July 17, 2020 [1 favorite]
I went down to the banks of the Mississippi River on Wednesday and got a really good view of the comet with my binoculars. I also got a whole bunch of mosquito bites, but that's to be expected.
posted by vibrotronica at 1:15 PM on July 17, 2020
posted by vibrotronica at 1:15 PM on July 17, 2020
It'll make more of a difference as it gets higher above the horizon but the further you can get from city lights, the better your view should be. I drove from downtown Toronto to Orangeville (70km) to see Hyakutake back in 96 and it was a splendid sight. I'm guessing 24 years of sprawl will mean driving a fair bit further for this comet.
posted by bonobothegreat at 2:00 PM on July 17, 2020
posted by bonobothegreat at 2:00 PM on July 17, 2020
If you have even a vague idea of the general area of the sky the comet is in, you can get a pic by pointing a recent-ish phone that direction.
Low-light mode on an iPhone, for example, works automatically. An exposure of 3-4 seconds is all you need to get a shot of the comet. There are also tons of apps that allow you to manually do long exposures. Just brace the phone on a solid surface and make sure the flash is off. Same for even the cheapest cameras that don't have much manual control.
If you just want to see the comet, even low-power binoculars will show a lot of detail regardless of whether you're in an urban area and despite it not being very apparent to the naked eye.
posted by theory at 2:05 PM on July 17, 2020 [1 favorite]
Low-light mode on an iPhone, for example, works automatically. An exposure of 3-4 seconds is all you need to get a shot of the comet. There are also tons of apps that allow you to manually do long exposures. Just brace the phone on a solid surface and make sure the flash is off. Same for even the cheapest cameras that don't have much manual control.
If you just want to see the comet, even low-power binoculars will show a lot of detail regardless of whether you're in an urban area and despite it not being very apparent to the naked eye.
posted by theory at 2:05 PM on July 17, 2020 [1 favorite]
Hale Bopp was the best I’ve seen. Was fortunate to be on a camping trip out in a very dark-sky part of west Texas & we put our chairs out & watched it for a couple hours while yakking & smoking cigars. One of the more memorable evenings of my life.
Pan Starrs a few years ago was good, but was just barely naked-eye visible, all the way out in the Davis Mountains. Was still worth the trip though, as one evening it was only a couple degrees to the left of the thin new crescent moon.
posted by Devils Rancher at 4:32 PM on July 17, 2020
Pan Starrs a few years ago was good, but was just barely naked-eye visible, all the way out in the Davis Mountains. Was still worth the trip though, as one evening it was only a couple degrees to the left of the thin new crescent moon.
posted by Devils Rancher at 4:32 PM on July 17, 2020
It's a far far cry from Hyakutake and Hale-Bopp though.
This, very much this. I drove out to Isanti County, Minnesota to escape the city light pollution last night, and got a fairly good view. It's worth seeing, but it's not super bright the way Hale-Bopp was.
Turn around and look in the other direction, though, and Jupiter and Saturn are putting on a nice show as well. They're the two planets to the south, if you're viewing from Northern latitudes about an hour after sunset.
posted by gimonca at 8:38 PM on July 17, 2020
This, very much this. I drove out to Isanti County, Minnesota to escape the city light pollution last night, and got a fairly good view. It's worth seeing, but it's not super bright the way Hale-Bopp was.
Turn around and look in the other direction, though, and Jupiter and Saturn are putting on a nice show as well. They're the two planets to the south, if you're viewing from Northern latitudes about an hour after sunset.
posted by gimonca at 8:38 PM on July 17, 2020
I was looking for it from High Park in Toronto this evening and couldn’t see anything with the naked eye. A guy asked me what I was looking for and I answered in a friendly manner which was his opening to tell me about radiation coming from geo-stationary satellites and his concern around their effects on the human body.
posted by bonobothegreat at 10:31 PM on July 17, 2020
posted by bonobothegreat at 10:31 PM on July 17, 2020
Too many times to count I’ve set alarms to view sky events and awoken to cloudy skies. So it was a huge treat to find the comet this evening! With binoculars it’s lovely; without, yes, it looks like a smudge but is still very cool.
posted by kinnakeet at 12:51 AM on July 18, 2020 [2 favorites]
posted by kinnakeet at 12:51 AM on July 18, 2020 [2 favorites]
Finally saw it last night! It was still above the trees after the sky got dark enough for it to be naked-eye visible.
posted by dirigibleman at 9:32 AM on July 18, 2020
posted by dirigibleman at 9:32 AM on July 18, 2020
bonobothegreat, I've been driving towards Uxbridge for things like the Perseids for the last couple of years as dark sky maps show that it's relatively dark out there. Basically go up the 404 up to Davis and then head east. You'll hit relatively dark skies before you get to Uxbridge, just stop off the side of the road and you're good. I have a friend who just moved outside Uxbridge and yesterday I asked him if he had seen the comet yet, he went out later at night and was able to see it. I'm going to take my kids out on Friday night to hopefully see it as long as the weather holds up.
posted by any portmanteau in a storm at 1:57 PM on July 21, 2020
posted by any portmanteau in a storm at 1:57 PM on July 21, 2020
Cool. Thanks for the tip.
posted by bonobothegreat at 9:14 AM on July 23, 2020
posted by bonobothegreat at 9:14 AM on July 23, 2020
I went up on Friday night and once the app told us exactly where to look we could see the comet but it just looked like any other star. We also saw a shooting star as well as a satellite. The satellite was pretty neat to see, it was like a star quickly moving across the sky in a straight line.
posted by any portmanteau in a storm at 1:56 PM on July 27, 2020
posted by any portmanteau in a storm at 1:56 PM on July 27, 2020
If it looked like any other star then it wasn't the comet you were looking at. I've been able to see it every night for the past weeks and it has consistently had a visible tail heading in the 2 o'clock direction. the head of the comet is bright, but a smudge that does not twinkle, again, unlike a star.
posted by OHenryPacey at 10:06 AM on July 28, 2020
posted by OHenryPacey at 10:06 AM on July 28, 2020
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And it's observed nearly 160,000 of them (over 30,000 of them being new objects not observed before), including the NEOWISE comet.
posted by tclark at 8:56 PM on July 16, 2020 [10 favorites]