Expert: Tom Whiting - 7/31/2006

Question
Foremaost i am grateful that you have made yourself available free of charge.

Now then, my brothers and i have been wondering abotu shooting stars, which as you know are really space debris that burn up i the earth's atmosphere.

we are not recisely certain why they burn, but are generally disposed to the idea that they are movign at such tremendous speeds that the friction presented by the particles in earth's upper atmosphere cause tem to deterorate in the shinign streaks we commonly call shootign stars.

if this is true, would it be correct to assume that if they were to somehow entewr at a much slower rate, that they would not burn up? after all, on the surface of earth there is are much mroe particles, and we are in now danger of combusting due to friction with them.

also, when the strek of a shootign star ends, does it verify that the debris is completely deterorated or is it possible for the streak to end but not all of the space rock to jave burned up?

also, can you suggest a suitably enjoyable telescope for amateur star gazers. something we could see some planets with, although ina reasonable price range and not extensively difficult to assemble and operate.

also, i seem tor ecall that soemthign burned up into jupiter a decade or so ago, and that many astonomers watched it. can you tell me what it was, and if it was visible from earth with bare eyes?

i apologise for the length of my inquiry.

-willem  

Answer
Hi Willem (and your brothers),
Well, thank you for the questions and I am very glad to help
you out.
Last Question First....Yes, that was Comet Shoemaker-Levy 9
that collided with Jupiter back in July 1994, and no, it was
not visible to the naked eye....but it was visible in a very
small telescopes, as small as 6 inch mirrors  (typical beginners
telescope).  About a year earlier, that comet made a very close
approach to Jupiter, so Jupiter's immense gravity ripped the
comet into over 20 separate pieces  (see Roche's limit and
tidal forces) which went into an elliptical orbit, ending with a known collision on the back side of Jupiter, as viewed from the Earth,  about a year later, July 1994.
So since the collision point was about 10 degrees of longitude on the back side of Jupiter, no one on the Earth
could view the actual collisions....but in about 30 minutes
later (Jupiter rotates very fast, one rotation is 9 Hr 55 minutes)
us Earth observers could see the black spots, the results of
the collision.  Also, since the collisions were near the limb
(edge of the planet) many big telescopes were also able to
record the resulting plume or fireball of the tremendous
explosions as the hot gases rose very high, and could be
observed at the limb a few minutes later.
Although it's a little technical, you can read all about it at
http://www.physics.sfasu.edu/astro/sl9/cometfaq2.html

So  now, on to your other questions, in the proper order.
But first, we astronomers prefer you use the term "meteor"
rather than falling, or shooting stars....as you properly guessed, the incoming particles have nothing to do with
stars, it's small space junk, so we prefer the "meteor" term.  and by the way, it's a meteoroid before atmospheric entry, and if it hits the surface of the Earth, then it's called a meteorite.
So it's only a meteor when it's giving off light and heat,
interacting with the upper atmosphere.

Most of your reasoning is exactly correct.....
1.  Yes, it's the tremendous velocity of the particle and friction
with the upper atmosphere that causes the "burning" and light we see...most are only a grain of sand size....a pea or
marble size is generally a bright fireball or bolide!
A baseball sized meteor will make a spectacular show across
the sky!  Most meteors burn up and are completely destroyed
in the upper atmosphere, say from 100 down to 60 miles,
and usually very quickly, like one or two seconds.
Yes, it's the velocity, because recall your basic kinetic
energy formula, which equals 1/2 the mass, times  the
velocity SQUARED.   It's that velocity squared factor that
produces all the energy and friction with the air.
Most meteors enter the atmosphere at anywhere from a
couple of miles per second, up to 100 miles per second.

2.  You ask, could a meteor enter so slowly that it would not
burn up, but just fall to the Earth....Yes, but....that would
be very very rare (and probably no one would then see it)!
Remember, most of the speed is the Earth itself...we rotate
at 1000 miles per hour at the Equator (which isn't very fast),
but the Earth is moving at 18.5 miles per SECOND around
the sun...that's pretty fast....AND the entire Solar System
is moving around the Milky Way Galaxy at about
200 miles per second...that's pretty fast too.
The only situation I can think of where that could happen
would be a particle that the Earth is very slowly overtaking
in the eastern sky (since we rotate and revolve around the
sun eastward)....but even then, the Earth's gravity would
begin to accelerate the overtaken particle down toward the
ground.....so in most cases, even at only 1 mile per second,
the meteor particle will probably still slowly burn up.
But theoretically, I guess it's still possible not to burn up,
in very rare cases.

3. Well, we're in no danger of "burning up" because we don't
move through our atmosphere at those speeds....one exception to that is the returning Space Shuttle, at about
5 miles per second, (18,000 miles per hour) and as you know, it lights up the sky like a meteor on re-entry.  The other exception is (was- the plane has been decommissioned) the USA  SR-71 spy plane, "the Black Bird, the Habu, etc.....which traveled through the air at close to 3000 miles per hour....it wing leading edges actually started to glow red due to friction with the air, at those high speeds.
But for the rest of us, I don't think we'll ever be traveling at
close to 3000 miles per hour.

4.  Yes, in nearly every case, 99.99+% of the time, maybe even
higher....the  high speed "grain of sand" is completely destroyed, but the remaining "soot" does fall to the Earth eventually...that soot can be found on freshly fallen snow on mountain tops, but it is very small, like just several microns in diameter.  But it's been sampled, generally on Antarctica snowfalls, and detected and analyzed.
But every so often, a meteoroid is big enough, say football
size, that it survives the flight through the atmosphere, and
impacts the Earth....of course, since 70% of our planet is
water, unseen ocean falls are the most common, for the very
few that survive.   But even those that survive the plunge,
typically they slow to terminal velocity, 120 miles per hour,
so the meteor falls AS IF dropped from an aircraft.
That is all 'science fiction' for those people that report a
"hot, flaming meteor" hitting the Earth....IN FACT, most
freshly fallen meteorites are usually super cold and have
a layer of frost on them!  There is just not enough time
in the atmospheric flight to heat up the interior of a space
rock that is probably hundreds of degrees below zero
prior to it's flight through the atmosphere...and only the
very outer layers are burning off...so the remaining "rock"
is typically stone cold, or colder!  (You guys didn't know that, did you?)  ;-)   The only exception to that would be if
the meteor was huge, like 100 meters or greater in diameter,
and if you ever saw one of those flaming into the Earth, you'd
probably be dead in a few minutes anyway, from the pressure and shock wave created, or the water tsunami created by an
ocean impact!

5.  Ok, in our great hobby of astronomy, equipment (scopes)
come LAST, not first.  Knowledge comes first...so, make
your first "scope" a cheap pair of binoculars and a good
star chart....(Sailors of the seas need great charts (maps), and so do sailors of the stars).
Then go out at night and learn...that's right...self-teach
yourself, the constellations.  It's not really that hard...if you
can learn and memorize four adjoining countries...like
Portugal, Spain, France, Germany...then you can also learn
4 adjoining constellations...they are simply areas of the sky
for identification purposes.....so you can also learn and
memorize Gemini, Cancer, Leo, and Virgo.  YOU need this
background....you can't find the Armory in Columbus, Ohio
until you first know where Ohio (constellation) is, then the
city of Columbus (a naked-eye star), then offset 10 Km to
the south to find the Armory....this ain't rocket science....we
do exactly the same thing in the night sky.
Also, what do you want to specialize in?  Deep sky objects,
Lunar/Planetary details, comet hunting, variable stars,
splitting doubles/multiple stars, asteroid hunting, nova
hunting, etc etc?  (And you WILL specialize because there is just too much out there to view)  There is a scope you can purchase, or build, that maximizes each one of those activities..................scopes are like airplanes,
all airplanes fly, but you don't send a bomber to do a
fighter's job...scopes are also like that.....Otherwise, we'd
all have the SAME type of scope....but we don't , because
different amateur astronomers have different interests in
the night sky.  So this is another reason, equipment comes
LAST, not first.  Besides, if you can't point your finger to
the Andromeda Galaxy, the Beehive star cluster, the beautiful
double star Albireo, the Lagoon Nebula, Saturn, Uranus....ALL naked eye objects in a dark sky....how on Earth are you going to point a telescope that typically only "sees"
a 1/2 degree circle (about the size of the naked-eye moon)
toward those objects?  You can't.  Right now, a telescope is
probably useless to you because, except for the moon and
a few bright planets, you don't know where else to point it!)
So your first task is to learn the naked-eye night sky.  For more information and advice for the novice observer, please see our club website at
http://www.velocity.net/~bwhiting/
and punch on Tom Whiting's Sound Advice to the Novice Astronomer.....
But if you really do buy a scope, keep it SIMPLE...get a Dobsonian mounted scope with no computer or goto aids....those make you lazy and you won't learn the night sky...and plan on a minimum of $500 USD and a 6  or  8 inch mirror,  Newtonian Design, for your first scope.  Any smaller, is almost worthless, and any cheaper, and you'll have a piece
of junk that won't work except on the moon and the boats
in the lake.  Sorry, but it's just the laws of optics....see our
club website, as I said, as to why.

Well, hope all this has helped you guys,
Clear Skies,
Tom Whiting
Erie, PA  USA
President...ECMOG