Once again, we – on Earth – will be passed by a Near-Earth Asteroid. This time on April 12th. Don’t worry! Its nearest approach will be about 38 thousand kilometers (23,800 miles). For reference, the diameter of the Earth is about 8000 miles. The size of this is a rock that you could hide a Ford Expedition behind.
Near Earth Asteroid…Date……….Miss Distance…..Velocity (km/s)…..Diameter (meters)……
Figure 1: Parameters of Near-Earth encounter with 2021GW4
Figure 2: Orbits of Earth, the Moon and 2021GW4. These are calculated without the Earth’s gravity effect on the asteroid’s orbit. The red line suggests what might happen in reality.
The question on everyone’s lips is always what will happen IF this asteroid were to collide with the Earth. It will not do that, OK?
People just love to imagine catastrophe and asteroids are their greatest opportunity. So, I have developed a macro to calculate such a disaster given the mass of the asteroid and the relative velocity of that asteroid with the Earth. Now, there are many variables (also referred to as “parameters”) that effect such calculations and I have made many assumptions – based on “average” values of density – and so forth. So, if you calculate a different number, please let me know – and show your work!
With all those disclaimers, I will say that the asteroid’s impact – if its course were to coincide with the position of the Earth (which WILL NOT HAPPEN, by the way!) – would generate an explosion equivalent to 1.3 kilotons of TNT. This is calculated by the Kinetic Energy using the estimated mass of the NEA and the velocity from the table in figure 1.
For reference, the bombing of Hiroshima yielded an explosion estimated at 12 to 18 kilotons. For an extreme example the “Tsar Bomba” detonated by the Soviet Union in 1961 yielded about 50 Megatons (50,000 Kilotons). So, we have already done far more damage on our own than this particular object could heap upon us.
The night sky is pretty much a mystery to most City Dwellers. The glare of city light drowns out all but the brightest stars – and planets don’t do much better. If you are interested, I can tell you where to look to see these far-off worlds. If you were not interested, you would have stopped reading after the first sentence. So, at this point, I know my audience.
Astronomers have known – for centuries – a secret that reveals the true nature of God! Doubt me if you must, but listen to what I have to say and see if you do not agree.
These astronomers, from centuries ago until now, have all either learned by experience or have been told of an odd thing called “averted vision”.
This situation comes about because vision is ruled by the light detecting nerves in your eye. There are two types, “rods” (low-light sensitive and color insensitive) and “cones” (color sensitive and high resolution but 40 times less sensitive to light in general)
The center of your field-of-view is just lousy with cones and that’s how you read small fonts and so forth. Your peripheral vision (“in the corner of your eye”) is loaded with rods that detect light quite well, but are not particularly descriptive about it. It is described in more detail at Sky at Night Magazine
So, over the centuries astronomers learned to look away slightly in order to see more of what they wanted to see. Sounds a bit silly, does it not?
“…When I was a child I caught a fleeting glimpse Out of the corner of my eye I turned to look but it was gone…”
You will notice that this short quote pretty much describes what I have been talking about. The rest of the lyrics have been interpreted by others quite differently as you will see at that link above.
So, what of this claim about the true nature of God? This is the first clue I had that God is the biggest (of course) Practical Joker in the Universe.
Imagine this conversation:
God: Do you want to see that better?
Mortal: Well…yes, I do.
God: Don’t look at it!
Mortal: Say What?!
God: You heard me!
Mortal: Hey, wow!
God: Told ya! (chuckle)
Some will tell you that this is just “Evolution”. Others might say that it is God’s Will.
And at least one man asked, what’s the difference?* It was Pope John Paul II – who had no problem with “Evolution”.
*About Life in general, not just averted vision
Somehow a small planet created beings capable of asking how they came to be there. It is the only such place we know of. This even though we have actively looked for extra-terrestrial life and/or intelligence – with steadily increasing range, accuracy and sensitivity – for about a Century.
Say, perhaps all of Life is God’s Practical Joke on the Universe! 😉
The night sky is pretty much a mystery to most City Dwellers. The glare of city light drowns out all but the brightest stars – and planets don’t do much better. If you are interested, I can tell you where to look to see these far-off worlds. If you were not interested, you would have stopped reading after the first sentence. So, at this point, I know my audience. 😉
Our story so far: Your Humble Reporter has shown you Saturn and Jupiter and Mars in October– in both cases using the moon as a pointer. This time the crescent moon will be the landmark for Venus – and possibly Mercury. I include a sky map for November 12 at 6:00 (6 AM) – from Heavens-Above.com – below.
The moon is always near “crescent” phase when it is over by those planets, because they are always near the Sun. I will pause now while y’all think about that! 😉
The sky map can be used by printing it out and holding it (or your phone, with the chart displayed) over your head. You need to orient the chart with the sky, of course. If you know where the North Star is, use that – or there are more than one compass apps for your phone to be downloaded for free.
In the early-to-mid part of the Twentieth Century, it was thought that Venus might be a steamy jungle-covered planet – beneath the all-concealing clouds that made such speculations plausible. An alternate speculation was that Venus was covered with a vast ocean of soda water – created by absorption of the thick carbon dioxide atmosphere. Carbons dioxide does not rule out life – quite the reverse! Plants love the stuff! Also, the exact composition of the atmosphere was not known until relatively recently (if you are as old as I am) 😉
All that interesting imagination did not come close to the real story, which is a crushing, thick atmosphere, dry as a bone and hot enough to melt Lead on the surface.
There is a more welcoming place on Venus, however. This is an exert from my article “Habitability” (as yet unpublished):
“So, if by “habitable” we mean: A natural environment where we could walk around “in shirt-sleeves” (as they say) while breathing the unaltered atmosphere: No, there is no such place beyond Earth.
Well, perhaps if we allow that we might have to bring our own air, but keep the “shirt-sleeve” aspect? There are some interesting possibilities. What’s needed is something like the atmospheric pressure that we tolerate here and that can actually be found at Venus. Not on any surface, you understand, but high in the atmosphere. 
At about 50 kilometers (30 miles) above the surface of Venus, the atmospheric pressure is about half that of Earth at sea level. The temperature is roughly 27 °C (81° F). This should be survivable while breathing air that you’ve brought with you. The temperature changes with altitude as the pressure does and some combination of the two might be found where outdoor activity might be possible. Details of what sort of oxygen/nitrogen (helium?) mixture to breathe at what pressures will have to be determined. High-altitude aerospace engineers and deep-sea divers could probably work this out in no time.
The alert reader will notice that this CO2 rich environment – with its Earthlike pressure and temperature (and sunlight) could well support unprotected plant life. There is no reason that a crop of fast- growing plants could not supply food, as well as the oxygen required for breathing and buoyancy.
*Note that this “outdoor” activity will be limited to walking around on exposed decks in some sort of zeppelin – we had such vehicles in the early years of the previous century. No great leap of technology there. This hypothetical airship – suspended by balloons filled with any combination of oxygen or nitrogen – would float in the heavier CO2. There is, however a haze of sulfuric acid in the carbon dioxide of the Venusian atmosphere that must be considered.”
Habitability – Steve Campbell
Back to the viewing on Nov 12: The elusive Planet Mercury may also be visible – about half-way between the Moon and the horizon. Not for me, mind you, since I have the enormous, glaring Houston Metroplex to the East of me – but maybe for you. Once again, you can change the viewing location on theHeavens-Above.commap to depict your own sky.
Mercury, back in the “old days” was thought to be “tidally locked” (always with the same side to the Sun). Mercury is in an elliptical orbit and it turns out that it is weirdly revolving in a 2/3 resonance that is also a stable response to tides. They thought Venus was “tidally locked”, as well. The truth about Venus is that its day is longer than its year. So weird is this story that I don’t have time to explain it. This is another illustration of how Scientists are always right, except when they are wrong. When somebody wants to talk to you about “Settled Science” read them this article! 😉
Mercury’s rotation axis is almost perfectly oriented at 90 degrees to its orbit, which means that the craters at its poles are permanently shadowed from the Sun. Observations of those polar regions of Mercury have produced evidence of water ice in those always-dark craters. So, the closest planet to the Sun has been proven to have water ice, as does the third planet (that’s us!). Yet, the second planet is the hottest and driest (i.e., no water- solid or liquid but perhaps some gas). Again, nobody thought so until it was made obvious to them.
Before we sent space probes to those planets in the 60’s and 70’s (as witnessed by your Science Nerd Humble – and Ancient – Reporter), we didn’t know this stuff and what we thought we knew turned out to be wrong.
7/31/2020 Comet 2020 F3 is now receding back into the distant reaches of the Solar System. As yet, however, it is still closer to the Earth than the Sun and closer to the Sun than the Earth is. This should make one appreciate just how rare and fleeting is the opportunity to see these events with “Eyes Only”.
In point of fact, I – your humble narrator – did not actually see this comet without the use of binoculars. And even then, it was only a fleeting glimpse – out of the corner of my watering eye (1).
“Above the planet on a wing and a prayer My grubby halo, a vapour trail in the empty air Across the clouds I see my shadow fly Out of the corner of my watering eye A dream unthreatened by the morning light Could blow this soul right through the roof of the night”
That was on July 24th when a rare cloudless Northern sky presented itself and I was awake at the proper time. I attempted to show this to all the immediate family. For the record, it is painfully difficult to describe how to point the binoculars to another person, despite placing the student in the recently vacated footprints of the Astronomy Nerd and the use of tree branches as reference points. And even when it works, the family member is underwhelmed by the dim little streak that is seen.
In figure 2, below is seen the orbital configuration of the comet as of July 31st. The comet – known by the mundane press as ”NEOWISE” (which is the name of the space probe that discovered the comet, modified by its extended mission prefix) is actually named only “C/2020 F3”
A Norwedian collegue and reader was also able to spot the comet – despite being so far North that he had to wait until a half-hour before Midnight for the sky to be dark enough. As he pointed out, that left him with about one hour of observation time until the sky woould be brightening again.
Spotted it now with a Nikon 10-22×50
Still hard, but knowing where to look is key.
I have searched for a definition of “Wola” and can only come up with a Polish district:
Comet 2020 F3 is creeping up in the post-sunset sky. On July 14, I may have seen it dimly through the distant haze – in moments when the nearer and opaque clouds drifted out from in front. In those 20 seconds, I saw what could be the nucleus of the comet through a pair of binoculars. Any hint of a tail was not to be seen. But, the sky map doesn’t show anything else in that part of the sky that would be bright enough to show through the haze.
I don’t call out family or friends for these desperate attempts at observation. Mostly because – when asked to point out this astronomical wonder – I am forced to say,
“See that cloud over there?”
“Yes, I see it.”
“The comet is behind that cloud.”
“How do you know?”
“Because that’s where the sky map says it should be.”
“I mean, how do you know for sure?”
That’s why astronomers have been considered lunatics – for centuries. You may think I’m joking, so look up a Danish fellow named Tycho Brahe. (Teak – oh Bra-hay)
Figure 2: Sky map as found at the July 14 link on the previous update.
On the next day, July 15, the forecast was for clear skies after sunset, but I made the Rookie Mistake of not setting an alarm and slept through the opportunity. Astronomers have to set their schedule by when the observation presents itself.
As Shakespeare wrote, “It is the stars, the stars above us, govern our condition.”
Shakespeare also wrote, “The fault, dear Brutus, is not in our stars, but in ourselves”.
So, I have no excuse for not setting the alarm.
July 16-19, 2020 9:00 PM See that cloud? The comet is behind it.
In a message from my long-time reader and cousin:
My friend is in OK right now. I gave her all the info last week. I just got this message:
“WE SAW NEOWISE!!!!!
It was so awesome!! I was so excited like a kid walking into Disney World!! It took us awhile to see it but it has to be very dark and we were out in the country.. The tail was very clear and all the stars around it just highlighted the beauty…”
I am happy to hear that someone has seen this comet. It is starting to dim now as it recedes from the Sun. It has yet to make its closest approach to the Earth, but any brightening by proximity is more than canceled by a more distant Sun and a calming of gas and dust emissions due to less Solar heat and radiation.
Comet 2020 F3 is making the promised rise in the Northern sky. It shows no sign of breaking up. It is approaching its closest point to Earth and should hold its brightness until then.
Now is your chance.
The comet is as bright as can be expected. It is coming into a position where it should be visible in the early evening sometime in the next week or two. Infra-red observations indicate that the nucleus of the comet is about five kilometers (three miles) across, so it is not likely to fall apart. The brightness should be comparable to the stars of the Big Dipper, at least.
Sky Maps for July 13 through 17 (from SpaceWeather.com) are linked here:
Comet 2020 F3 is now “eyes only” visible in the morning sky, low in the East, just before sunrise. I have not been able to see it because of persistent clouds in the Houston area. But, other, more fortunate readers may want to check Spaceweather.com for photosand finder charts. Clear Skys and Good Viewing! – Steve
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 C/20020 F3 (hereinafter mostly referred to simply as “F3”) is now very close to the Sun as viewed from Earth. Pointing highly complicated and hideously expensive telescopes near the sun is a process to be avoided and so there have been few observations of F3 lately.
Let me make this perfectly clear – do not try to see the comet at this time when it is near the Sun!
On the other hand, some instruments are specifically designed to look at the part of the sky around the Sun. One is aboard a probe called Solar and Heliospheric Observatory (SOHO*) that orbits between Earth and Sun in what is called a “halo orbit” around a “Lagrange point” (which has nothing to do with any personal service establishments in the City of La Grange, Texas).
*Note that the acronym should be SHO or SAHO, but SOHO sounded cooler so they use that.
The short story is that SOHO studies the Sun and its atmosphere and comets appear in its field of view from time to time. F3 has made an appearance there and somebody has measured the brightness about once per day and added that to the COBS (another fractured acronym) database.
As the comet nears the Sun, it heats up, emits more gas and dust and brightens in excess of distance effect. In the figure below, you can see that the brightness has come close to second magnitude. Nevertheless – do not try to see it! SOHO is out in Space and has specially designed instruments – you aren’t and don’t. There will come a time when you can look at it safely and I will be glad to tell you when.
Below is the SOHO image of the comet for today, June 26.
NEOWISE is a project name associated with the Wide Field Infrared Survey Explorer (WISE) which has discovered 28 comets and 313 Near Earth Objects. That is why Your Humble Narrator does not use “NEOWISE” or any other project or imaging system name as the name of a comet (or other object), like the mundane press so often do. Because…which one?! You would think that the SOHO people would realize this…but NO! 😉
Update: I find that the text additions on this graphic are not from the SOHO folks, but added by a third party who shall remain nameless!
In the future, I will quote SOHO graphics myself and add any text for clarification – with attribution to myself alone.
Yet another comet approaches and has already been promoted as an “eyes only” event. Not by me, of course – because I have learned the hard way that comets almost always disappoint – mostly because astronomy nerds are too quick to get excited about such things.
It is called C/2020 F3 and is approaching from the southern part of the Solar System. I include (figure 1 below) a diagram (made with JPL’s Small Body Orbit Diagram Utility and appropriately annotated by your Humble Narrator.)
As before, I have calculated the expected change of brightness due to distance alone (green curve on the graph below) and plotted the observed brightness (blue dots) for the comet. See figure 2 below.
I will be watching this one as well. Updates as they occur.