Comet 2020 F8 has dimmed well below “eyes only” visibility and seems destined for obscurity. Now that it has passed Perigee (closest distance to the Earth) and is passing Perihelion (closest distance to the sun), there can be no expectation of brightening, based on distance alone. Another outburst of erupted gas and dust also seems unlikely, so this is probably the end of the story for C/2020 F8.
Figure 1. Predicted “distance only” brightness and actual observationsFigure 2: Comet’s path through the Solar System.
Next, I am thinking of a project to confirm the rotation period of a historical comet using the phase analysis as described in my Comet Update of April 26. This will utilize that data at the Comet Observation database. It will serve as proof that I am doing this analysis correctly.
“Comet Observation database (COBS)saw first light in 2010 and is maintained by Crni Vrh Observatory. It is a free and unique service for comet observers worldwide which allows submission, display and analysis of comet data in a single location.
Amateur astronomers can make valuable contributions to comet science by observing comets and submitting their observations to COBS as professional astronomers typically do not have telescope time required to acquire regular observations. We therefore encourage comet observers worldwide to submit their observations and contribute to the COBS database.”
Comet 2020 F8 has dimmed from its last outburst and is now just barely qualified to be “eyes only visible”. I call it that only in the abstract since I have attempted to spot it several times with binoculars without success. I live on the west side of Houston and the place where the comet is theoretically visible is in the northeastern sky – which is awash in city-light at best – just before dawn. My carefully chosen location is down south on a road that leads to Brazos Bend State Park where I was a volunteer telescope operator at the George Observatory.
You may ask why I did not use that telescope to view the comet. It is that the public viewing program at “The George” was suspended late last year for renovations to the observatory and museum facilities. It was all set for a grand re-opening when the current disruption concerning the Communist Chinese Xi Jinping Virus began.
My attempts at viewing the comet took place on mornings this past week when skies were allegedly clear. None were successful – due mostly to the aforementioned urban skies. The path of the comet is from the southern extreme of the Solar System – crossing into the northern skies – where it is now found – and exiting back to the south. Because it is closer to the Sun now, it can only be seen in the early morning. Later this month it will appear in the evening sky just after sunset. More on that later.
The diagram in Figure 1 shows the current positions of the comet and Earth. Mercury and Venus are seen but not labeled. I dotted the comet’s path when it occupies the southern part of the Solar System. With a considerable imaginative effort (and taking into account the direction of Earth and the comet), you can understand why it only appears in the early morning sky now and will appear just after sunset later.
Figure 1: Comet’s path through the Solar System. Orbits of Mercury and Venus are shown but not labeled.
Figure 2 is the updated light curve and shows the decline in brightness. Since it has now passed its closest point to the Earth, we could expect it to dim – if it were not still approaching the Sun. The Sun will illuminate the comet more – and heat it, which may induce another outburst of brightness.
Or…it could fall apart and disappear. No guarantees, you understand. 😉
The observations are being “handed over” from southern hemisphere observers to those in the north. That gap near the 15th is a result. There were single observations each day, but so far from the norm that I did not bother to plot them.
Figure 2. Predicted “distance only” brightness and actual observations
Comet 2020 F8 is now visible with “eyes only” – but just barely. The eruption of dust and gas that has brightened the comet so quickly has abated and the debris has apparently dispersed. Part of that has become the tail that is blown away by the solar wind and gas. The tail has been divided and twisted by the Sun’s magnetic field. Below isyet another photo by Gerald Rhemann @ Farm Tivoli, Namibia on May 4, 2020.
Figure 1:
This is when the comet was at about magnitude 5.3. It is in fact a montage of five images. As of this writing, 2020 F8 is showing at magnitude 5.8. You will recognize the graph below as my calculation of brightness change due to total distance (Sun/Comet/Earth) with the average daily observed magnitude.
Below is an updated “light curve” that shows the distance-based brightness calculation with the daily average observations. The red dotted lines show the dates when the comet will be closest to the Earth (Perigee) an closest to the Sun (Perihelion). The green points show the combined effect on brightness due to the Sun/Comet/Earth distance.
Figure 2. The “distance only” prediction and the observed (daily average) brightness. Distance data from JPL Small Body Database Browser. Observations from Comet Observation Database.
The Comet has undergone three eruptions of brightness. The first was the eruption of Hydrogen (it is thought) that made the comet detectable in the first place. That part is not plotted. The next was around April 19th. That one complicated my rotation calculations. The third was the recent that peaked on May 31st.
2020 F8 is crossing into the Northern Hemisphere and I will attempt to spot it with binoculars or a telescope. If I locate it I will make sky charts for you readers. Orbit diagram below.
Figure 3: Orbit diagram.
No doubt you are wondering what will be next. There could be another eruption. Comets are composed of ice and rocks. The ice can be any light elements or compounds like CO2 or water – all with differing points of sublimation (like evaporation, but straight from solid to gas). As those ices vaporize, dust and rocks are released.
Or, the comet could break apart and fade from view – like 2019 Y4 did recently.
Or, anything in between
That’s just the way comets are. 😉
Let me share a reader’s question:
HI Steve,
Good article. Have you tried to see the comet yourself, or is beyond amateurs ability to view it?
Thanks, (Road Trip Interest Group Member)
_______________________________________________
Dear Road Trip Interest Group Member,
The comet (2020 F8) is just now coming in to a part of the sky where it will be visible in the Northern Hemisphere. It will be near the square of Pegasus in the early morning. It is low on the Eastern horizon at 5 AM now but the Sun rises soon after. I have not yet seen it for two reasons:
1. The City of Houston is East of where I am and drowning out the sky with city-glare.
2. The weather is persistently cloudy.
I have two viewing location in mind out near the George Observatory. The skies out there are darker because the neighbors all practice downward directed lighting – probably by state law since the Observatory is on state property.
If I can get a clear morning, I will drive out and have a look in the next few days. I will attach a finder chart(from Sky and Telescope Website )and include same in the next update. You can use that (which shows you the position relative to the constellations) and the phone app called Heavens-Above (to find where to look for the constellations at any moment) to find the comet.
I won’t encourage others until I – myself – can catch a glimpse.
Another Near Earth Object encounter. This time with a unique announcement:
Figure 1.
Notice that 2020 JJ has an anomalous distance of encounter of zero AU. It is rounded off, of course. The managers of this source will be contacted to encourage more decimal places! By other sources, I find the “miss” distance to be about 16,200 miles which is indeed less than 0.1 Lunar Distances.
This, again is worthy of a more detailed diagram with a better picture of the Earth (Thanks, NASA!).
The approaching asteroid did not pass across the celestial equator – where all the geosynchronous communication satellites are – but further to the South.
The JPL Small Body Database Browser, which is also the source for the “circle and arrows” diagrams you have seen on these pages, has undoubtedly given us a more accurate figure. However, it does have some limitations, which are clearly explained in the website:
“This orbit viewer was implemented using two-body methods, and hence should not be used for determining accurate long-term trajectories (over several years or decades) or planetary encounter circumstances.”
The alert readers (most of you) will point out that “planetary encounter circumstances” is exactly what I am talking about. That statement means that when asteroids get close to a planet, their mutual gravity has a significant effect that is not calculated in this utility. So, that 16,200 miss distance is not keenly accurate and almost certainly too large. Not only that, but it also means that the orbit after the near encounter will have been altered. It will need to be recalculated and replaced in the database.
JPL has a utility for that, called the “Horizons system” and NASA has an organization to keep track of these things (and studies methods to avoid collisions) called the Planetary Defense Coordination Office. That said, rocks this small (about 13 feet across) are not easily detected far in advance. They are also less destructive should they fall to Earth. This one was small compared to the Chelyabinskmeteor.
Comet 2020 F8 is now visible with “eyes only”. But not from the Northern Hemisphere. I hasten to explain that the “crosshairs” appearing (below) on the brighter stars are artifacts of the telescope construction – diffractions caused by the mounting bracket of the secondary mirror.
Figure 1: Taken by Gerald Rhemann on April 27, 2020 @ Farm Tivoli, Namibia
This is when the comet was at about magnitude 6.3. As of this writing, 2020 F8 is showing at magnitude 5.3. You will recognize the graph below as my calculation of brightness change due to total distance (Sun/Comet/Earth) with the average daily observed magnitude. I warned you that comets can’t be predicted with simple models like that and now you see what I meant.
Figure 2. The “distance only” prediction and the observed (daily average) brightness
Again, the differences are due to eruptions of gas and dust, making a much more reflective target. The comet now qualifies for “eyes only” visibility. It is still something for which you would need to take a trip outside your sophisticated urban environment. But don’t even bother because – except for my readers in the Southern Hemisphere – it is still below the southern horizon. I am working on some sky charts for Lima, Peru. But that still requires a road trip to a dark sky. There may be something for you city dwellers later.
Figure 3
Update May 5: In Lima, the comet is in the Eastern sky just before dawn (unfortunately looking right across the well-lit city) at about 25 degrees altitude. The sun will be rising soon so here is the standard warning: Do not look at or near the Sun with binoculars or a telescope! Blindness may result.
There is also a meteor shower this morning, coming out of the West East and streaking across toward the city ocean.* Also, look for Mars, Jupiter and Saturn together in the Southeast. There are conflicting weather reports. One says mostly clear. If that works, “Sigrid, te quito la bruma Limeña!”. Otherwise – same as usual.
*Doh!
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In 1979, Skylab – America’s first space station – was falling out of orbit and my sister called me – her space nerd brother – to worry about this thing that she feared would fall on her new baby. I tried to explain that the Earth is so big and the Skylab so small (relatively speaking) that the chances were nil that any person on Earth would be anywhere near where it fell.
I went on to point out that there are natural meteorites that fall to Earth constantly and they could amount to the equivalent of thousands of Skylabs every year. She never worried about those!
After that, she was not just worried – more like terrified!
I have since learned to advise people that they are more likely to be hit by a train, bitten by a shark and struck by lightning – all at the same time – than to be struck by anything falling from the sky. There is exactly one case of a person being hit by a meteorite. The lady was badly bruised, but not fatally.
I told you that to blunt the effect of telling you the following:
Another Near Earth Object passed by the Earth on April 28th, 2020. I have checked a couple of reliable sources and I can tell you that the nearest it came was about 29 thousand miles. And that sounds like a lot, since the earth itself is only about 8000 miles in diameter,
However, the NEO does come into our “territory” since we have satellites orbiting the Earth. You might think that satellites are only hundreds of miles above the Earth and that is where you are mistaken. I decided that those little diagrams with circles and arrows are insufficient for this one. Please see the diagram in Figure 1 for details.
As you see, the NEO this week is close enough to be of definite interest. However, it passed to the South of Earth – nowhere near the “belt” of geosynchronous satellites over the equator and over twice as far as the “cloud” of GPS satellites. And, of course nowhere near the Space Station.
The asteroid is about 60 feet across. Satellites are flimsy aluminum gadgets and would crumble before the NEO. But Space is big and satellites are small.
Another Near Earth Asteroid has zoomed by while no one was looking on April 22nd. It may surprise the readers to learn that these things are so common that I only consider the ones that pass as close as the Moon to be of interest. This one was at 0.4 Lunar Distances or about 95,542 miles.
Figure 1
The culprit is 2020 HF5 – a small rock, as asteroids go – that is only 52 feet across. These encounters are listed at https://spaceweather.com/ – just scroll down a bit to find a table.
The rock in question is very much is roughly the same size as an asteroid that exploded over Челябинске in Russia on my 58th birthday. (Feb 15, 2013) . The heat of re-entry, combined with the tremendous air pressure of its hyper-sonic trajectory caused it to explode at 12 to 15 miles above the surface.
There was a Russian teacher – Yulia Karbysheva – about my age who, like me, had been trained in Civil Defense exercises in elementary school. They taught us what to do in a nuclear attack. When the meteor lit up the sky, she had her students hide under the desks – as she (and I) had been trained to do. When the asteroid exploded and the shock wave arrived, it shattered all the windows and sent shards of glass over the desks – with the students safely beneath same. After almost a half century, that training finally paid off – for the students. Unfortunately, she was so concerned with the fourth-graders that she remained standing and was seriously injured. In all, about 112 people were hospitalized, mostly cuts from flying glass. There were some cases of flash blindness and ultraviolet burns. Don’t look at the flash! I learned that instinctively as a welder.
Our more recent visitor was similar in size, but with only about 1/2 the relative velocity as that meteor and would have about the one fourth the explosive potential. About 117 kilotons – 9 Hiroshima bombs equivalent.
What’s that? Oh…it’s the town’s name – “Chelyabinsk”.
Comet C/2019 Y4 has broken into pieces that are scattering and fading in brightness despite being closer to the Sun and Earth. I will include a Hubble Space Telescope photo here:
Figure 1
It will not be a “Great Comet”.
However…
Comet 2020 F8 is now visible in a small telescope or binoculars and will probably be – at the very least – visible without such aids very soon. Below is a recent image from Universetoday.com
Figure 2
But, you won’t see it now because it is in the Southern sky and is being observed from New Zealand and Australia and other points in the Southern Hemisphere. It will arc over the Northern sky soon. In the previous update, I graphed the brightness to be expected due to distance alone. You can take this as a prediction of 6.3 as the peak magnitude. But, we all know that is almost certainly wrong – because we don’t have enough information. I have added the daily average observed magnitude (orange dots) in Figure 3, below.
Figure 3.
The observations are, indeed following the prediction – somewhat. The differences can be attributed to eruptions of gas and dust, but also to the comet’s rotation. In college, I learned a method of analyzing sparsely collected observations to detect periodic changes. It goes something like this:
We cannot monitor objects in telescopes with enough resolution in time to detect a periodic variation along one cycle of rotation or pulsation. However, since we expect the oscillations to be more-or-less uniform over time, we can collect points from different oscillations, over an extended period and graph them as a single cycle.
But this requires that we know the period of the cycle. Astronomers have been historically starved for data and come up with some desperate solutions. In this case, we can try every possible period of oscillation, put the resulting data on graphs, and pick the one that looks like we think it should for a single cycle. In the olden days, this laborious amount of calculation could be out-sourced to graduate students or assigned as homework for undergraduates. If you want to imagine doing such calculations “by hand” go ahead. Me, I don’t have to use imagination because I did it – a few times.
The observations have a time associated with them. We establish a “zero point” and calculate a time value for each magnitude. Then each observation time is divided by the trial period. That leaves a fraction that is the position in the single “combined” oscillation we intend to graph. Then we change the trial period and repeat – a lot. Below is a “perfect” theoretical graph to be kept in mind while looking through all the trial graphs.
Figure 4. Ignore the numbers, which are “made-up” anyway. Concentrate on the shape.
And before you ask “why didn’t you use a computer at UT in 1976, Steve?”, I should tell you that in the 70’s, a computer with a tiny fraction of your telephone’s capability was a huge machine in a large room attended by several “operators” who scheduled calculations on that hideously expensive device for days in advance. The data and the programs (apps) were read in on punch cards and the output was printed on green-and-white paper. What “memory“ was available held the simple operating system and your bare-bones program and input data for the time it took to complete the “job”. Then your data and program were immediately replaced with the next job. No time was available for undergraduate homework.
Now we have Excel spreadsheets instead of graduate students or IBM 360 “mainframes”. The needed calculations and a graph on the screen for one trial period is accomplished in a split second with a single click. The graph below was selected as “plausible” after 291 clicks. This indicates a period of four hours, 51 minutes.
Figure 5
The points plotted come from 74 observations over 14 days. I should mention that these were not the “raw observations” but were adjusted to remove the distance-related brightening (that green curve in Figure 3).
This was the “best-looking” result, but there were other “candidates” at six hours, seven minutes and at eight hours, 10 minutes. Nothing even close to “plausible” was found after that, up to and including a 30-hour trial period.
So, if you hear later that the comet has been determined to be rotating at a period like any of those – remember that you heard it here first! Otherwise, well I was wrong. Science has a long history of being wrong, so that’s OK. The important part is to not insist on your theory in the face of contrary evidence and accept that you were wrong. (Are you listening, Global Warming Devotees?) 😉
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Comets are particularly unpredictable phenomena. The current case is C/2019 Y4, which has apparently broken up into at least three pieces – which at last sight were drifting away from each other. It’s visual magnitude has gone from a sudden brightening to 7.8, but then dropped to 8.8 after the break-up and shows no sign of recovering. This, despite the fact that is nearer to the Sun and the Earth than before. It is not visible to the naked eye, even in clear, dark skies. You might find it with a medium amateur telescope.
There is another, more recently discovered comet in the Solar System called C/2020 F8. It, too has undergone a sudden brightening, but is still a bit to dim to see – even in that theoretical dark, clear sky. Since it is in the Southern sky right now, you could not see it anyway.
I have made some diagrams of both comets with the JPL Small-Body Database Browser and added some explanatory text. The planets are all in the same orientations and positions in both.
Figure 1
Figure 2
“So, what next? “, you may ask. Well, as these comets approach the Earth and Sun – at different rates since the Earth and Sun are 1 AU apart – they will brighten. We cam predict the change due to distance alone. Below is a graph of distances predicted over time for C/2019 Y4 (refer to figure 1). The data are from the aforementioned JPL Small-Body Database Browser The graph was generated by your humble narrator in Excel.
Figure 3
The increase of brightness to be expected (if nothing about the comet itself changes) can be predicted by the total distance involved. Keep in mind that light spreads out such that a reduction of ½ the distance will result in 4 times the brightness. Remember that on this stellar Magnitude scale a reduction of 1 magnitude is the equivalent of more than a doubling (about 2.5 times) in brightness. I don’t make these rules, OK?
This needs some calibration since it calculates only differences. That calibration is taken from a recent observation as noted on the graph (also Excel) that follows.
Figure 4
The conclusion is that the peak brightness will be still below naked-eye visibility – around May 28th. Having said that, you will remember that this exercise assumes that the comet itself will not change. But that’s silly! We just saw it increase suddenly in brightness (far in excess of expectation) and then dim again! That was from eruptions of vaporizing ices, that apparently broke this comet into pieces. I told you these things are unpredictable, did I not?
So, why do this calculation of brightness due to proximity? Because it is all we can do! Keep that in mind the next time someone tells you they can predict the climate. 😉
C/2020 F8
The same sort of calculation can be done for this Johnie-come-lately comet that just showed up. I will skip all the intermediate explanations and go straight to the prediction chart.
Figure 5
You see that the new comet is likely to be brighter than poor old C/2019 Y4. It will probably become magnitude 6.3 – bright enough to see without binoculars or a telescope – out of city lights, in a dark clear sky -but just barely!
And, just now we have news of an observation from the Comet Observation Database . For April 19th (late in the day) the brightness was measured at magnitude 6.8. You can see the red cross on the graph. That is, however, one of four observations on that day – the other three were all magnitude 7.5. To change the whole prediction on a single observation would not be reasonable, so I will wait to do so until a few more observations are made. Did I mention that these things are unpredictable?
You may ask, “Steve, why did you choose such an uncertain occupation?”
I did not choose Astronomy. Astronomy chose me. It is actually a hobby because, while I wanted to be Carl Sagan, I found out they already had one. So, I wound up looking down through the Earth instead, because someone would pay me for that. Now I have nothing better to do. Well, I have other things to do – yes. But, who wants to mow the yard again?
Before you write me to say, “Why didn’t you photograph the comet, Steve?” – this image is from a telescope with 8 times the light-gathering power of mine. Add to that, the fact that they took 120 second exposures…twenty of them. To do that they had to track the comet as it moved through the background stars that make the streaks you see. Their telescope is guided by sophisticated computerized servos, while my ‘scope is on a mount made from a plywood box and is guided by “pushing with your hand”. Then they stacked those 20 photos together to make this image. These are professional Astronomers in a Swiss observatory while I am just a guy in a driveway in Houston.
I warn you that this is what Literature students call “a bear”! But my preliminary read tells me that the comet fragmentation could pre-sage a disappearance or it may be associated with sudden eruptions of activity that result in a brightening. A long-winded way of saying “Anything could happen”, this is. 😉
There are many reasons a comet might break up but the main two in this case (in my humble opinion) are probably thermal stress and gaseous eruptions of sub-surface ice bodies.
Update: A recently discovered comet in the Southern sky has undergone an “outburst” and is already as bright as Y4. It is not yet in the databases, so no cool diagrams, yet. Details in the next post.
