There were at some observations, after the comet left SOHO’s field of view. Seven are now documented in the COBS database as bright as magnitude 1.0 – comparable to the brightest stars in the sky.
See it also in the now “standard” graphic for my updates- below.
After the SOHO data (red circle) are “conventional” telescope observations and you might think that a decline is happening. Don’t take that to the bank, because these observations are from telescopes looking just above the horizon and just before dawn. That is a lot of atmosphere to look through and a lot of twilight interfering. Estimates of brightness of the comet might be inexact.
The “Calibrated Prediction” (green dots) has about July 17th as the peak brightness. That is based solely on the distances (Sun to Comet to Earth) and assumes that the comet reflection characteristics never change. That is – of course – never true of comets when they warm up near the sun – emitting gas and dust chaotically. So, why do the “prediction”? Because then we know how much of the brightness variation may be attributed to distance alone. We can take that effect out to study the changes in reflection characteristics…including periodic variations that must be due to rotation.
If this sounds like an “inexact science” – good! All Science is inexact! However, a good Scientist can give you some idea of just how inexact his science is. 😉
Challenging the Dawn
Oscar Martín Mesonero of Salamanca, Spain, also saw the comet in morning twilight. See his photo below (also from Spaceweather.com)
The comet is here seen as more-or-less “head on” and seems to vaguely show a bifurcated (two part) tail. That is not unusual as gas particles may be ionized and affected by the Sun’s magnetic fields and solar wind. The dust particles tend to stream out behind the orbital direction of the comet’s path, while still blown around by solar wind. Sometimes the two line up as viewed from Earth, other times, not so.
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 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.
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.
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.
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.
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.
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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:
It will not be a “Great Comet”.
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
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.
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.
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.
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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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.
Comet 2019 Y4 (hereinafter called simply “Y4”) is still approaching the inner Solar System and still being observed. It occurs to me that I have not posted an actual image of this comet, So, that will be figure 1:
I promised a diagram to explain Y4’s path through the Solar System. To quote my previous comment:
“ I’ll include a diagram in the next update. But, for now, imagine yourself as very small and standing on an old-school LP record. The gaps between songs are the orbits of the planets. You are on the third gap and the comet is at the 4th gap but high above the LP. It will come in past all the rings and dive into the record inside Mercury’s orbit (1st gap) on May 30th. It will emerge on the bottom side and make a similar, but mirrored, exit path. It is moving at a tremendous velocity because it has been falling toward the Sun since about 1844. -Steve”
With this verbal imagery and the diagram below (figure 2), I hope the situation is well-explained.
I have plotted the position of the Y4 on March 13th and April 10th. Those dates were chosen from the a magnitude chart because the comets was at the same brightness on both. In the meantime, the comet has moved much closer to the Sun. Please see the magnitude chart below and pick up the story below that.
Comets don’t shine like stars, they only reflect the sunlight that shines on them. Before I go further, please remember that magnitude is a smaller number for brighter objects.
If the comet were unchanging, then the fact that it is closer should mean that the brightness would increase from magnitude 8.7 to about 7.9 (just take my word for that:-). Clearly, something did change, because the comet brightened too quickly and then dimmed again. What happened is why comets are so unpredictable.
The comet body, warmed by the sun will begin to “evaporate”. Frozen gasses are vaporized and form a gas cloud around the “nucleus” and are blown away by the radiation from the Sun and the rush of sub-atomic particles called the “solar wind”. That is what makes the comet’s “tail”. The bigger ball of gas reflected more light and so the brightening.
The dimming? Maybe:
The vaporizing gas may have “unglued” the body of the nucleus and it started falling apart.
The stuff beneath the frozen gasses is darker rock and reflects less light.
The ice that was volatile at this temperature has all vaporized.
What will happen next? Maybe:
The comet may fall apart completely and disappear.
Less volatile ices may vaporize when the comet is closer – and therefore hotter – and that will renew the brightness
That last option at least leaves open the possibility that the show is not over.
So, you were warned – and that last part may well be happening now. Below is a collection of all photometric (CCD) observations of Comet 2019Y4 from March 7. Below that is a graph of the distance from the comet to the Sun (orange) and from the comet to Earth (blue) for the same period. The distances are in Astronomical Units – the distance from the Earth to the Sun – about 93 Million miles
You see that:
* The comet was brightening until about April first. Then it declined rapidly until today April 7th.
* In that time, it has gotten closer to the sun, which illuminates the comet better than before and closer to the Earth – where we should see it brighter than before – even without the additional illumination by the Sun.
* See the Conclusions below the charts
One expects a comet to lose mass as it is blown away by the solar wind – that is what makes the “tail”. That would cause a dimming due to a smaller reflective surface and smaller “gas ball” surrounding. This will be offset by brightening by being nearer to the Sun and Earth.
In this case, the dimming is faster than the brightening due to being nearer. The comet is probably wasting away quickly – on its way to disappearing for good.
But, I could be wrong. 🙂
Hasta Luego, Steve
P.S. If you have any questions please use the comments section (Leave a Reply) below and I will answer for all the readers who may have had the same question. Thanks SBC
The weather has been even worse than usual for astronomy. Don’t misunderstand – around here, there are just awful conditions for viewing at the best of times. But cloudy weather has been unusually frequent lately. The comet is still not very bright, in an area of the sky that is devoid of any bright stars for guidance and in a direction that is particularly afflicted with trees and city-light. Nevertheless, I have attempted to spot the comet with binoculars several times – without success.
Attempting to photograph what could not be seen visually of Comet 2019 Y4, I am struggling with an unfamiliar DSLR (digital single lens reflex) camera. Just the camera on a tripod and guessing at various settings of exposure, “film” speed, focus and aperture. No, I didn’t see the comet. I was barely able to detect any stars in the city-light washed-out sky.
One thing that stood out was some much more concentrated and colorful points of light. I wondered what these could be since they were far to point-like to be anything in the sky that was not even properly focused. Despite that these were intense and focused bits of light.
The bright spot in the red circle of figure 1 – what could make such undeniable point-like events? The answer came back – after considerable snaky-eyed concentration – these must be traces of cosmic rays. As it turns out – I was right. The lens of the camera has nothing to do with these images. The high-energy particles pass through the camera body from any and all directions. If at a low angle to the “chip”, the image extends to an oblong shape, like the examples below.
The irony is that the comet, which is right here in the Solar System – along with stars that are in the visible “neighborhood” are so elusive, while cosmic rays, which may originate half-way across the universe, are showing up clearly as “volunteers”
It has become clear that I will have to make a trip out to a dark sky location to see this comet. That may take a while, so I will hone my skills with the binoculars and camera, in the meantime.
Others are not so unfortunate in their efforts to see this comet. Collected observations of the comet show that it has dimmed in the last week. Please see figure 4.
Comets show up all the time and are observed by telescope. The rarity is of “naked eye visible” comets. My personal experience is that they show up aboutonce per decade (click here).
I was due for another comet and it has shown up.
The media are incorrectly calling it “Comet Atlas”. Search for that name and about three dozen comets will pop up because ATLAS is the acronym for the name of the observing system that discovered it, not that of the comet itself. The Asteroid Terrestrial-impact Last Alert System is – as the name reveals – a project to find asteroids. It does occasionally discover a comet and it finds thousands of supernovas – in other galaxies – none are even close to “naked-eye objects”.
As most nerdy people know, comets frequently defy prediction and disappoint millions of viewers. Thus far, Comet 2019 Y4 has only defied prediction by rapidly brightening far in excess of prediction. Please see graphic below.
The green line plots the predicted brightness. Points in blue are from actual observations. Note that this comet has grown to near naked eye visibility (from a dark sky, not in city lights).
Where to see this? A screen grab of a sky map from Heavens-Above.com for 3/25 to 3/27 (with text and markings by your humble narrator to “Un-nerd” same) appears below.
Update: I tried, unsuccessfully, to see this comet with binoculars – in glaringly lit-up Houston skies on March 24. The latest brightness observed (by professionals) is Mag. 7.6 as of 3/25. But, it will get brighter, soon.