That was close. Tunguska was pretty bad, too. Funny how now the two
events have both been in Russia.

Steve

On 2013-02-16, Steve B wrote:
That was close. Tunguska was pretty bad, too. Funny how now the two
events have both been in Russia.

I was thinking about this too, my explanation is that Russia has a
large area of territory, so it is more likely that a meteor would hit
Russia, than Luxembourg or Denmark.

i

Steve B wrote:

That was close. Tunguska was pretty bad, too. Funny how now the two
events have both been in Russia.


The third wasn't.

Ignoramus21620 wrote:

On 2013-02-16, Steve B wrote:
That was close. Tunguska was pretty bad, too. Funny how now the two
events have both been in Russia.

I was thinking about this too, my explanation is that Russia has a
large area of territory, so it is more likely that a meteor would hit
Russia, than Luxembourg or Denmark.

Most likely explanation and two events some 105 years apart isn't a very
big statistical sample. Recall the various known meteor craters in other
parts of the world for other samples and the distribution sure looks
random.

On 2013-02-16, Pete C. wrote:

Ignoramus21620 wrote:

On 2013-02-16, Steve B wrote:
That was close. Tunguska was pretty bad, too. Funny how now the two
events have both been in Russia.

I was thinking about this too, my explanation is that Russia has a
large area of territory, so it is more likely that a meteor would hit
Russia, than Luxembourg or Denmark.

Most likely explanation and two events some 105 years apart isn't a very
big statistical sample. Recall the various known meteor craters in other
parts of the world for other samples and the distribution sure looks
random.

I agree. I am slightly fascinated with asteroids.

i

"Ignoramus21620" wrote in
message ...
On 2013-02-16, Steve B wrote:
That was close. Tunguska was pretty bad, too. Funny how now the
two
events have both been in Russia.

I was thinking about this too, my explanation is that Russia has a
large area of territory, so it is more likely that a meteor would
hit
Russia, than Luxembourg or Denmark.

i

Canada has some very large circular features too:
http://dsc.discovery.com/news/2006/1...ategory=travel
http://en.wikipedia.org/wiki/Manicouagan_crater
The glaciers have wiped away the evidence of surface ejecta.

Long-period comets have orbits above or below the plane of the planets
(which was scrubbed clean?) and so are most likely to strike at the
latitude of their approach angle, which is centered in front of them.
There is relatively little land to leave a crater on south of the
equator.
http://www.astronomynotes.com/solfluf/s8.htm
"The long period comet orbits are oriented in all different random
angles while the short period comets orbits are within about 30
degrees of the solar system plane."

Long period meteors that don't release water vapor trails like comets
are hard to detect. We'd probably never notice one coming straight at
us since it doesn't appear to move over time.
jsw

On 2013-02-16, Jim Wilkins wrote:

"Ignoramus21620" wrote in
message ...
On 2013-02-16, Steve B wrote:
That was close. Tunguska was pretty bad, too. Funny how now the
two
events have both been in Russia.

I was thinking about this too, my explanation is that Russia has a
large area of territory, so it is more likely that a meteor would
hit
Russia, than Luxembourg or Denmark.

i

Canada has some very large circular features too:
http://dsc.discovery.com/news/2006/1...ategory=travel
http://en.wikipedia.org/wiki/Manicouagan_crater
The glaciers have wiped away the evidence of surface ejecta.

Long-period comets have orbits above or below the plane of the planets
(which was scrubbed clean?) and so are most likely to strike at the
latitude of their approach angle, which is centered in front of them.
There is relatively little land to leave a crater on south of the
equator.
http://www.astronomynotes.com/solfluf/s8.htm
"The long period comet orbits are oriented in all different random
angles while the short period comets orbits are within about 30
degrees of the solar system plane."

Long period meteors that don't release water vapor trails like comets
are hard to detect. We'd probably never notice one coming straight at
us since it doesn't appear to move over time.
jsw



Scary and true!

Ignoramus329 wrote in
:

On 2013-02-16, Jim Wilkins wrote:
Long period meteors that don't release water vapor trails like comets
are hard to detect. We'd probably never notice one coming straight at
us since it doesn't appear to move over time.

Scary and true!

It might be scary if it were true, but it's complete nonsense.

There is no such thing as "one coming straight at us" if for no other reason than that we are
not sitting still. The direction from Earth to *anything* changes continually, because we're in
an orbit about 190 million miles wide around the Sun. Anything "coming straight at us" today
certainly won't be tomorrow, because the planet will have moved one and a half million
miles.

On Sat, 16 Feb 2013 10:56:28 -0500, "Jim Wilkins"
wrote:


"Ignoramus21620" wrote in
message ...
On 2013-02-16, Steve B wrote:
That was close. Tunguska was pretty bad, too. Funny how now the
two
events have both been in Russia.

I was thinking about this too, my explanation is that Russia has a
large area of territory, so it is more likely that a meteor would
hit
Russia, than Luxembourg or Denmark.

i

Canada has some very large circular features too:
http://dsc.discovery.com/news/2006/1...ategory=travel
http://en.wikipedia.org/wiki/Manicouagan_crater
The glaciers have wiped away the evidence of surface ejecta.

I've been to Manicouagan 4 times on winter camping trips. We spent
most of the time in the mountains that were thrown up on the west
shore of the lake -- the white area in the bottom of the photo.

There's a series of five dams between the lake and the St Lawrence. In
atlases that predate the dam closest to the lake (Manic 5), the lake
is horseshoe shaped rather than a complete ring.

A large sectioned and polished fragment of nickel-iron collected at
Manicouagan is on display in the Harvard natural history museum.

--
Ned Simmons

"Doug Miller" wrote in message
...
Ignoramus329 wrote in
:

On 2013-02-16, Jim Wilkins wrote:
Long period meteors that don't release water vapor trails like
comets
are hard to detect. We'd probably never notice one coming straight
at
us since it doesn't appear to move over time.

Scary and true!

It might be scary if it were true, but it's complete nonsense.

There is no such thing as "one coming straight at us" if for no
other reason than that we are
not sitting still. The direction from Earth to *anything* changes
continually, because we're in
an orbit about 190 million miles wide around the Sun. Anything
"coming straight at us" today
certainly won't be tomorrow, because the planet will have moved one
and a half million
miles.


If it approaches on a tangent from ahead or behind it won't have much
relative motion against the stars.

So little is known on the Tunguska event - but it might be that the
two are related. Might be a stream in orbit that will hit Russia every
100 years or so. Something to look out for.

Martin

On 2/15/2013 11:45 PM, Steve B wrote:
That was close. Tunguska was pretty bad, too. Funny how now the two
events have both been in Russia.

Steve

"Jim Wilkins" wrote in :

"Doug Miller" wrote in message
...
Ignoramus329 wrote in
:

On 2013-02-16, Jim Wilkins wrote:
Long period meteors that don't release water vapor trails like
comets
are hard to detect. We'd probably never notice one coming straight
at
us since it doesn't appear to move over time.

Scary and true!

It might be scary if it were true, but it's complete nonsense.

There is no such thing as "one coming straight at us" if for no
other reason than that we are
not sitting still. The direction from Earth to *anything* changes
continually, because we're in
an orbit about 190 million miles wide around the Sun. Anything
"coming straight at us" today
certainly won't be tomorrow, because the planet will have moved one
and a half million
miles.


If it approaches on a tangent from ahead or behind it won't have much
relative motion against the stars.

Maybe not immediately -- but just wait an hour or two.

What part of "one and a half million miles a day" are you having trouble understanding?

"Doug Miller" wrote in message
What part of "one and a half million miles a day" are you having
trouble understanding?

If you are chasing another car at 100 MPH on a straight road across
Texas neither the car nor the horizon appears to move. Likewise an
object approaching along the line of Earth's orbital path may not
shift enough to notice against the starfield.
http://en.wikipedia.org/wiki/Blink_comparator

"Jim Wilkins" wrote in :

"Doug Miller" wrote in message
What part of "one and a half million miles a day" are you having
trouble understanding?

If you are chasing another car at 100 MPH on a straight road across
Texas neither the car nor the horizon appears to move.

True, but completely irrelevant, since neither the Earth nor any object that may be on a
collision course with us move in a straight line.

Likewise an
object approaching along the line of Earth's orbital path may not
shift enough to notice against the starfield.

Nonsense, for two reasons.

First, anything close enough to pose any danger of hitting us certainly will exhibit enough
apparent motion against the star field to be readily obvious.

Second, there is no such thing as "an object approaching along the line of Earth's orbital
path": the orbital path is an ellipse, not a straight line. The only way anything can be
*always* in "the line of Earth's orbital path" is if it is in the same exact orbit -- and if it's in the
same orbit, it can't be approaching us, because two objects in the same orbit are
necessarily moving at the same velocity.

Not to mention the fact that we would have noticed another body in the same orbit a long,
long time ago.

http://en.wikipedia.org/wiki/Blink_comparator

You didn't actually read that article, did you?

"In photographs taken a few days apart, rapidly moving objects such as asteroids and
comets would stand out, because they would appear to be jumping back and forth between
two positions, while all the other fixed stars stood still."

Which is exactly my point: only the stars would appear motionless. The Earth's motion
around the sun changes the direction to any nearby object enough that its motion relative to
the background will be immediately obvious after only a few days. We're not in danger of
being hit by a star. The things that might pose a danger -- asteroids and comets -- move
enough in just a few days to make their position and motion obvious.

"Doug Miller" wrote in message
...
"Jim Wilkins" wrote in
:


Second, there is no such thing as "an object approaching along the
line of Earth's orbital
path": the orbital path is an ellipse, not a straight line. The only
way anything can be
*always* in "the line of Earth's orbital path" is if it is in the
same exact orbit -- and if it's in the
same orbit, it can't be approaching us, because two objects in the
same orbit are
necessarily moving at the same velocity.


Okay, I took a nap and daydreamed of orbits, and realized that
anything nudged loose from the Oort cloud would have to pass through
Earth's orbit at a significant angle. The only way to make it tangent
is to assume a high initial velocity as it enters the Sun's gravity
well, so its hyperbolic path grazes our elliptical one.
Observationally that would mean it has higher than Solar escape
velocity.

"Jim Wilkins" wrote in
:

"Doug Miller" wrote in
message ...
"Jim Wilkins" wrote in
:


Second, there is no such thing as "an object approaching along
the line of Earth's orbital
path": the orbital path is an ellipse, not a straight line. The
only way anything can be
*always* in "the line of Earth's orbital path" is if it is in
the same exact orbit -- and if it's in the
same orbit, it can't be approaching us, because two objects in
the same orbit are
necessarily moving at the same velocity.


Okay, I took a nap and daydreamed of orbits, and realized that
anything nudged loose from the Oort cloud would have to pass
through Earth's orbit at a significant angle.

You're still not quite grasping this, I'm afraid. The point is that *anything*, regardless of
*where* it's coming from, will have to be at a significant angle to the planet's current path at
some seaon of the year. We're not at a fixed point in space, we're moving on an elliptical
orbit that's nearly two hundred million miles wide -- meaning that whatever its angle to us
today, that angle is going to be radically different three or six months from now, unless it's
light-years away (in which case it poses no danger).

The only way to
make it tangent is to assume a high initial velocity as it
enters the Sun's gravity well, so its hyperbolic path grazes our
elliptical one.

OK, let's assume the existence of an object on such a path. For it to pose any danger to us,
we'd have to be at the point of tangency at roughly the same time as the object. Let's further
suppose that to be the case.

A week *before* that, the Earth was ten million miles away from the point of intersection;
three months before, some 120 million miles -- and the object's path then would have not
been even remotely close to being tangent to ours, then. There would have been more than
enough of a difference in position for it to be spotted.

Bottom line: the probability of being hit by something big, without ever seeing it coming, is
effectively zero.