Tag: astronomy

Averted Vision

Posted November 25, 2020

Urban Astronomy

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?


Lyrics from Pink Floyd’s Comfortably Numb:

“…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!

(a pause)

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!  😉

Hasta Luego,




Urban Astronomy -Venus in November

Posted November 1, 2020

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. 

Skymap from Heavens-Above.com  

   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.

Still, Venus would be “A Nice Place to Visit”.  Well, not really nice…more like interesting – and deadly.

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.  [2]

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 the Heavens-Above.com map 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.

Ex Scientia, Trivia!


Urban Astronomy – Mars in October

October 19, 2020

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.  😉

Urban Astronomy

    I used the moon as a pointer for Saturn and Jupiter last time.  On October 29, the moon will be over by Mars in the evening sky.  I include a sky map for that date at 20:00 (8 PM) – from Heavens-Above.com” – below. 

Skymap from Heavens-Above.com  

 The moon will be near full at the time.  Mars happens to be near its closest to the Earth right now, as well.  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.

    When this reporter was young (an era also referred to as the Cretaceous Period), it was thought that Mars must certainly harbor life – at the very least, plant life – since it showed seasonal changes that were attributed to vegetation.  After a fly-by passage of the space probe Mariner 4 past Mars, it became apparent that Mars more closely resembled the crater-covered surface of our own moon.  Measurements of the atmospheric pressure on the Red Planet also made it quite unlikely that life as we know it – could survive on Mars.  Subsequent orbiters and landers have all failed to produce evidence of life on Mars.  The seasonal changes are now known to be dust patterns.  While the seasonal ice caps at the poles do contain water ice, they also are composed of carbon dioxide ice frozen out from the mostly CO2 (and extremely low-pressure) atmosphere.  Despite what many ill-informed Mars enthusiasts think, a human would need – for a walk on Mars – a space suit just like those used by Moonwalkers of the 1960’s/70’s.  Still, Mars would be “A Nice Place to Visit”

   Mars is where the moon is and about as bright as it ever gets.  Ya’ can’t miss it!

   Notice that Jupiter and Saturn are still hanging around at 8 PM – both are not far from where they were previously.  You should be able to spot them unaided,  but use the skymap, if not.

   Mars and the moon will be up all night, not just at 8 PM, so don’t try to use that as an excuse! 😉

Urban Astronomy


October 17, 2020 Introducing a new category

Despite this reporter’s career as a Geophysicist, he was an Astronomer by education.  These fields of study overlap when the Astronomy is “planetary”, since Geophysics involves the study of a particular planet to be found under the feet of a standing Astronomer.

  Your Humble narrator also has the habit of swimming – the only form of exercise he can manage to “stick to”.    If one can manage to show up at the pool early in the morning, a single-use swimming lane is to be obtained.  Large swimmers are particularly disadvantaged when “sharing” lanes – and said narrator is large. 

    Reporters are often instructed – by Editors – to refer to themselves in the third person (as above).  Since I am my own Editor here, I am now putting an end to that.

      If I can snag a lane in the outdoor pool, I am able to swim alone and in relative darkness, but even so there is considerable urban lighting with which to contend – not to mention the glaring lamps in the sides of the pool.  Nevertheless, the Astronomer/Swimmer takes note when there are visible stars and planets available for viewing.  

   A few months back, it happened that there were four planets visible from the outdoor swimming pool.  My natural tendency is to point things like this out perfect strangers.  However, some of the people around at this time of morning know me – by sight at least.  And we are all eccentric individuals, or we would not be swimming at 5 AM.  Since having four “Eyes Only” planets in the sky at once is a fairly rare thing, I pointed these out.  The average reaction was one of surprise.  They had no idea of what was over their heads.

The oldest Astronomer joke in the world is to promise to point out one more than the number of planets actually visible.  So, I promised five and pointed out four.  The punch line of this ancient bit of comedy relies on the audience to ask where the fifth one might be. Then the Astronomer replies,  “You’re standing on it!”.   Of course, no one asked about that fifth planet and the joke went flat.  Don’t you people have any curiosity?  Yes, it is an old joke, but none of them ever heard it before – because it is so old.

   Now, the interesting part about that stale humor – if you think about it – is the point it makes.  Specifically, that all those small round lights that this Swimmer is pointing out are actually massive worlds – a lot like the one we are standing on.  Some of them are stunningly larger, some smaller than our own planet.  Some are closer to – or farther from – the Sun.  There are places where “the world” is profoundly different from the “world” we experience.  With those thoughts, the human imagination is expanded beyond the mundane existence of day-to-day life.

  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 paragraph.  So, at this point, I know my audience.  😉

Some description of how far apart objects in the sky is needed, and “degrees” are another unfamiliar subject for Urbanites.  Extend your thumb and put it at arm’s-length and close one eye.  Now your thumb covers one degree of sky.  For Apollo 13 fans – this is why Jim Lovell was making the same weird gestures.  He was, in fact measuring the sky in degrees.

  Most Sophisticated Urbanites are also unfamiliar with compass directions.   The moon shows up pretty well, however.  So, I will use the moon to “landmark” where you Urbanites should look to find points of interest in the sky.  Those will be planets mostly, since at least four of same are bright enough to be seen in the City Glare.  The moon moves quickly across the starry sky, so pay attention to the dates and times. This first installment is for the night of October 22nd at 20:00 (8PM). 

Skymap from Heavens-Above website:  https://heavens-above.com/SkyChart2.aspx This link is calibrated from my patio. If you are near me, it will work for you. If not, you can change the location to your own house, with one of the links at left of the homepage.

At that date and time the moon will be near Jupiter and Saturn in the South-Southwestern sky.  Jupiter and Saturn are approaching a conjunction which will peak in December when the two planets will be within a tenth of one degree of each other – in the Earth’s sky, only.  They will actual be separated by about five Astronomical Units.  And – an AU is the distance from the Earth to the Sun (about 93,000,000 miles).

   All of my description, the thumb-and-one-eye-closed bit and the skychart are just illustrations.  This is Urban Astronomy – just look where the moon is!  😉

Comet Update 7/19/2020

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?”

“…I don’t.”

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 1:  The “Standard” graphic updated for July 19, 2020.  Green series: calculated for distance alone.  Blue series: Daily average of Observations (COBS)

Figure 2:  Sky map as found at the July 14 link on the previous update.

Figure 3: Sky map as modified by your humble narrator to reflect actual field conditions.

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:


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…”

My reply:

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.

Sky maps (from  Spaceweather.com): July 18, 19, 20.

And a 3 ½ minute exposure by James W. Young – also from spaceweather.com

Figure 4 Three and ½ minute exposure (tracked – or the stars would smear) by James W, Young – from Spaceweather.com

Clear Skies!




COBS:  https://cobs.si/analysis

Comet Update 7/3/2020


Comet 2020 F3 is still in one piece and still brightening.  As in the previous update it is rounding the Sun in the fast, sharp curve that includes the Perihelion (closest approach to the Sun).

See Figure 1, below

C2020_F3_Orbit_July 2
Figure 1:  Orbit of Comet 2020 F3 generated by JPL Small Body Database Orbit Diagram Widget.  Augmented and annotated by your humble narrator.

Spaceweather.com features a four-day movie of the comet’s appearance in  the LASCO instrument onboard the Sun-watching SOHO probe.

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.

Figure 2:  The Standard Graphic.

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.

Note that:

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)

Figure 3:  Mesonero’s photo of C/2020 F3

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.

Hasta Luego,


Comet Update – 6/26/2020

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.

Figure 1: Predicted vs. observed magnitude for Comet C/2020 F3

Below is the SOHO image of the comet for today, June 26.    

Figure 2: SOHO image of Comet 2020 F3 (they call it NEOWISE)

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.

Hasta Luego,


Comet Update 6/16/20

Comet Update C/2020 F3

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.)

Figure 1. Comets can originate from most any part of the sky. Many orbit near the plane of the solar system. This one does not.

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.

Figure 2. You can see why comet nerds are predicting this as a spectacular sight – it has far exceeded expectations already Remember Magnitude 6 is “eyes only” brightness. One prediction in “cometnerdland” is 2 to 3.

I will be watching this one as well.  Updates as they occur.

No, you can’t see it yet and neither can I.

Hasta Luego,


Comet Update 5/19/2020

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

Hasta Luego – Steve

NEO 2020 JJ 5/04/20

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 Chelyabinsk meteor.