APOD: Earthgrazer: Great Daylight Fireball (2009 March 02)

Comments and questions about the APOD on the main view screen.
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APOD: Earthgrazer: Great Daylight Fireball (2009 March 02)

Post by Hizairness » Mon Mar 02, 2009 7:07 am

shux, I wanted a new background image...

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Re: APOD 3-1-9 -- earth-grazing comet - low resolution ima

Post by StACase » Mon Mar 02, 2009 9:07 am

Very interesting, we have photos like this, and nothing of "UFO"s. One would think that if such a rare thing as a daylight meteor can be caught with such a great photo, that by now there would be good photos of "UFO"s. There aren't. Perhaps the reason is that there aren't any to photograph.
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Earth Grazing Meteor (2009 March 02)

Post by bystander » Mon Mar 02, 2009 1:21 pm


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Re: APOD 3-1-9 -- earth-grazing comet - low resolution ima

Post by Dr. Skeptic » Mon Mar 02, 2009 1:39 pm

StACase wrote:Very interesting, we have photos like this, and nothing of "UFO"s. One would think that if such a rare thing as a daylight meteor can be caught with such a great photo, that by now there would be good photos of "UFO"s. There aren't. Perhaps the reason is that there aren't any to photograph.
There is a plethora of daylight UFO photos documented, authentic alien spacecrafts - maybe not.
A photo by itself will never be adequate proof of alien technology, it will take an artifact in hand.

Also because we all know that Sunlight reflected off from H2O interferes with their warp drives proving daylight flight pictures are faked :wink:
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Re: Earth Grazing Meteor (2009 March 02)

Post by ta152h0 » Mon Mar 02, 2009 6:00 pm

I remember this and i think the meteor actually came back a year later and crashed somewhere on the planet. he was below the keyhole.
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Re: Earth Grazing Meteor (2009 March 02)

Post by aristarchusinexile » Mon Mar 02, 2009 6:45 pm

Another factor in global warming .. not a canoe in sight, only those infernal combustion engines.
Duty done .. the rain will stop as promised with the rainbow.
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Re: Earth Grazing Meteor (2009 March 02)

Post by neufer » Mon Mar 02, 2009 9:24 pm

ta152h0 wrote:I remember this and i think the meteor actually came back a year later and crashed somewhere on the planet. he was below the keyhole.
It should, indeed, return to the same orbital location but only many months after the earth, itself, had passed the former scene of the crime.

Because it left the earth with a relative northerly (and radially outward) velocity component of ~14 km/s it follows a long looping orbit with a period > 1 year (like most Apollo asteroids).

To hit a bullet with another bullet timing is as important as aim.
http://en.wikipedia.org/wiki/The_Great_Daylight_1972_Fireball wrote:
# 1972-08-10, US19720810 at 15 km/s above United States and Canada (first scientific observation)

<<The Great Daylight 1972 Fireball (or US19720810) is an Earth-grazing meteoroid which passed within 57 kilometres of the surface of the Earth at 20:29 UTC on August 10, 1972. It entered the Earth's atmosphere in daylight over Utah, United States (14:30 local time) and passed northwards leaving the atmosphere over Alberta, Canada. It was seen by many people and recorded on film and by space borne sensors.

Analysis of its appearance and trajectory showed it was a meteoroid about 3 metres (9.8 ft) (if a carbonaceous chondrite) to 14 metres (46 ft) (if made of cometary ices) in diameter in the Apollo asteroid class in an Earth-crossing orbit that would make a subsequent close approach to Earth in August 1997. In 1994, Czech astronomer Zdenek Ceplecha re-analysed the data and suggested the passage would have reduced the meteoroid's mass to about a third or half of its original mass.

The meteoroid's 100 second passage through the atmosphere reduced its velocity by about 800 metres per second (2,600 ft/s) and the whole encounter significantly changed its orbital inclination from 15 degrees to 8 degrees.>>
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Re: Earth Grazing Meteor (2009 March 02)

Post by Bravo4707 » Mon Mar 02, 2009 11:44 pm

Interesting picture and a good selection for APOD. Someone had to be pretty quick to catch it on film! (It's the 1970s.)

The comment in the caption describes the effect of the meteor passing through the earth's atmosphere and then returning to space as like a stone skipping off a lake. Perhaps a better description is the meteor punching through the atmosphere and departing, having missed the earth.

True, the atmosphere increases in density with decreasing altitude (let's say, distance toward the earth's center). However, the resultant outward force from differential drag on the top and bottom of the meteor should be extremely small, and should be overwhelmed by the force of gravity pulling the meteor toward the earth's center. The atmosphere goes from 1 ATM to zero in about 100,000 m (100 km), so the gradient of density across the leading face of a 3 meter crossection projectile is very small. Even with very turbulent drag, the differential outward force (away from earth's center) should be orders of magnitude less than the force of gravity.

If so, then the meteor will actually curve its path toward the earth's center (like a falling stone), rather than curve away from earth's center (like a skipping stone) while it is in transit through the atmosphere. BTW, the loss of speed from drag force has nothing to do with this effect. After all, the skipping stone is slowed by the surface of the water, but still manages to change direction upward.

I haven't gone through the calculations, so these comments amount to a thought experiment. I'd be interested to see someone actually calculate the difference in outward and inward forces from differential drag versus gravity. My guess is at least several orders of magnitude in favor of gravity!

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Re: Earth Grazing Meteor (2009 March 02)

Post by neufer » Tue Mar 03, 2009 1:17 am

Bravo4707 wrote:Interesting picture and a good selection for APOD. Someone had to be pretty quick to catch it on film! (It's the 1970s.)

The comment in the caption describes the effect of the meteor passing through the earth's atmosphere and then returning to space as like a stone skipping off a lake. Perhaps a better description is the meteor punching through the atmosphere and departing, having missed the earth.

True, the atmosphere increases in density with decreasing altitude (let's say, distance toward the earth's center). However, the resultant outward force from differential drag on the top and bottom of the meteor should be extremely small, and should be overwhelmed by the force of gravity pulling the meteor toward the earth's center. The atmosphere goes from 1 ATM to zero in about 100,000 m (100 km), so the gradient of density across the leading face of a 3 meter crossection projectile is very small. Even with very turbulent drag, the differential outward force (away from earth's center) should be orders of magnitude less than the force of gravity.

If so, then the meteor will actually curve its path toward the earth's center (like a falling stone), rather than curve away from earth's center (like a skipping stone) while it is in transit through the atmosphere. BTW, the loss of speed from drag force has nothing to do with this effect. After all, the skipping stone is slowed by the surface of the water, but still manages to change direction upward.

I haven't gone through the calculations, so these comments amount to a thought experiment. I'd be interested to see someone actually calculate the difference in outward and inward forces from differential drag versus gravity. My guess is at least several orders of magnitude in favor of gravity!
Good point, Bravo4707.

The meteor is essentially in a hyperbolic orbit with drag a second order effect
(and lift a third, or higher, order effect).
Art Neuendorffer

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Re: APOD 3-1-9 -- earth-grazing comet - low resolution ima

Post by Steve F Craig » Sat Nov 24, 2012 3:25 am

I observed the earth-grazing-comet as if first appeared, a tiny point of light, to the SSW of my position 7 miles N of Carter, Montana. My family's wheat harvest was underway and I had parked the '52 chevy 2-ton truck at the north end of a wheat strip looking south to watch for the combine drivers signal for a truck. It was a very clear and cloudless day so when I saw the tiny pin point of light appear I assumed what I had seen before that of looking up the exhaust of a fighter jet taking off from Gore Hill Airport in Great Falls, Montana. Much to my surprise the light didn't disappear the light grew bigger around. I got out of the truck and crossing my arms back and forth over my head managed to get my uncle Don to stop the combine he was operating and get out to look at where I was pointing. We watched the bright flaming ball approach very quickly from the deck next to the combine's cab. The meteor's main fireball seemed very large as it passed by just to the west. Coming off the big main ball of fire was a tail of yellow flame that fanned out leaving a monstrous boiling con trail. Inside the outwardly fanning flame was a very bright white flame which came to a sharp point behind the flaming meteor. The white flaming tail wasn't much longer than the diameter of the main fireball. My uncle wondered allowed if 'a satellite was dropping out of orbit'. I said, ' that is much to big for that', appearing much larger than the mid-day sun and moving so fast. The fire ball looked like it was on a trajectory to hit the earth at any moment. However the fireball headed off into the northeast disappearing behind it's billowing thick con trail. I thought a mushroom cloud would mark it's impact point and start a massive fire in the ripe wheat fields at any second. I could hardly believe it when I heard the meteor went back into space. Sincerely, Steve F Craig. Nov.23,2012

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Re: APOD 3-1-9 -- earth-grazing comet - low resolution ima

Post by Beyond » Sat Nov 24, 2012 4:24 am

WOW!!
To find the Truth, you must go Beyond.

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Re: APOD 3-1-9 -- earth-grazing comet - low resolution ima

Post by neufer » Sat Nov 24, 2012 3:30 pm

Steve F Craig wrote:
Coming off the big main ball of fire was a tail of yellow flame that fanned out leaving a monstrous boiling con trail. Inside the outwardly fanning flame was a very bright white flame which came to a sharp point behind the flaming meteor. The white flaming tail wasn't much longer than the diameter of the main fireball. My uncle wondered allowed if 'a satellite was dropping out of orbit'. I said, ' that is much to big for that', appearing much larger than the mid-day sun and moving so fast. The fire ball looked like it was on a trajectory to hit the earth at any moment. However the fireball headed off into the northeast disappearing behind it's billowing thick con trail. I thought a mushroom cloud would mark it's impact point and start a massive fire in the ripe wheat fields at any second. I could hardly believe it when I heard the meteor went back into space.>>
Art Neuendorffer