Interesting 'tease' ... Deimos (2009 March 16)

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Expand view Topic review: Interesting 'tease' ... Deimos (2009 March 16)

Re: Interesting 'tease' ... Deimos (2009 March 16)

by Pete » Wed Mar 18, 2009 2:42 am

neufer wrote:
  • A rocket ship travels with velocity v (vis a vis the earth) in direction x.

    The rocket ship sends a laser beam out the side of the ship in direction y;
    the rocket ship sends a stream of ping pong balls out the side of the ship in direction y;
    the rocket ship sticks a yardstick out the side of the ship in direction y.

    The laser beam, stream of ping pong balls & yardstick ALL DEFINE the y axis
    which is unaffected by motion in the direction x (except for translation)
    (Lorentz transformation ONLY affect the x axis & the time axis).

    Hence, the laser beam, stream of ping pong balls & yardstick are ALL
    unaffected by in both length & direction by the Lorentz transformation.
As for the individual photons of velocity c to
keep up with a rocket ship moving with velocity v
they must, indeed, (obviously) have an aberration of theta = arcsin(v/c)
such that [c sin(theta)] = v as you have correctly calculated.

You were simply confusing the aberration of individual photons with
the laser beam locked formation of those photons along the y axis.
*palm to face* I misread the question. As you effectively said, axes perpendicular to the direction of motion are not Lorentz transformed.
To convince myself of the answer to this question, i just picture the standard light clock example with one of the mirrors removed. The individual photons are relativistically beamed in the direction of motion, but the beam itself moves with the ship. Thanks!

Re: Deimos-March 16 APOD

by apodman » Wed Mar 18, 2009 2:17 am

neufer wrote:Why virtually the exact same letter?
Because all the ways to phrase the same simple request without embellishment turn out pretty much the same.

It was one sentence.
neufer wrote:Were you trying to prove something?
No. I was trying to get an application and a catalog. Didn't I say that?
neufer wrote:MIT probably did you a favor by being discouraging.
I didn't find them to be discouraging. I found them to be out to lunch.

Re: Deimos-March 16 APOD

by neufer » Wed Mar 18, 2009 12:08 am

apodman wrote:Four and a half years later, after accumulating impressive academic credentials, when it came time to do it for real, I sent virtually the exact same letter (with more mature handwriting) to MIT.
Why virtually the exact same letter? Were you trying to prove something?

I got a lot out of MIT but I also missed a lot of opportunities there (e.g., Philip Morrison's popular undergraduate astrophysics course). I also knew a lot of very smart guys who crashed & burned at MIT. MIT probably did you a favor by being discouraging.

Re: Deimos-March 16 APOD

by apodman » Tue Mar 17, 2009 10:50 pm

neufer wrote:I can remember a sophomore year physics quiz question from M.I.T. (1964)
Pete wrote:Okay, you went to MIT
In 1964, I dreamed of going to MIT. In 1965, I entered the 7th grade. My 7th grade teacher was substandard, but he gave us one valuable assignment: write to the college of your choice to request an application and a catalog of courses. This was intended as practice for the real thing a few years later. So I sent my request to MIT and they quickly sent me an application and a catalog. I enjoyed having the catalog which showed me what I could expect for coursework in various major fields of study. Four and a half years later, after accumulating impressive academic credentials, when it came time to do it for real, I sent virtually the exact same letter (with more mature handwriting) to MIT. In return I got not an application nor a catalog. Instead I got a letter with a pre-application. The letter explained that catalogs were expensive to print and mail, and they couldn't send them to just anyone. The letter also explained that they couldn't waste their time reviewing just anyone's application, so I would have to fill out the pre-application and send it in with the hope that they would send me a real application. They treated me worse than they had treated a 7th-grader. They showed themselves to be incapable of responding correctly to a simple request. I tossed their letter and pre-application in the garbage and never looked back.

Re: Interesting 'tease' ... Deimos (2009 March 16)

by neufer » Tue Mar 17, 2009 10:36 pm

bystander wrote:
neufer wrote:
  • As I was going to St Ives
    I met a man with seven wives
    And every wife had seven sacks
    And every sack had seven cats
    And every cat had seven kits
    Kits, cats, sacks, wives
    How many were going to St Ives?
Only one that I can be sure of, you. Don't know what the man and his wives, sacks, cats, and kits were doing.
  • <<St Ives, Cornwall: In 1999, the town was the first landfall of the Solar eclipse of August 11, 1999.
    A live BBC programme with Patrick Moore was sadly clouded out.

    Sir Patrick was always very close to his mother and she was a talented artist
    who lived with him at his Selsey home which is still colourfully decorated
    with many paintings of "bogeys", little friendly aliens, which she regularly
    produced and were sent out annually as Patrick's Christmas cards.>>
http://antwrp.gsfc.nasa.gov/apod/ap990810.html
http://antwrp.gsfc.nasa.gov/apod/ap990817.html
http://antwrp.gsfc.nasa.gov/apod/ap990818.html
http://antwrp.gsfc.nasa.gov/apod/ap990819.html
http://antwrp.gsfc.nasa.gov/apod/ap990820.html
http://antwrp.gsfc.nasa.gov/apod/ap990830.html
http://antwrp.gsfc.nasa.gov/apod/ap991105.html

Re: Interesting 'tease' ... Deimos (2009 March 16)

by bystander » Tue Mar 17, 2009 8:09 pm

neufer wrote:
  • As I was going to St Ives
    I met a man with seven wives

    And every wife had seven sacks
    And every sack had seven cats
    And every cat had seven kits

    Kits, cats, sacks, wives
    How many were going to St Ives?
Only one that I can be sure of, you. Don't know what the man and his wives, sacks, cats, and kits were doing.

Re: Interesting 'tease' ... Deimos (2009 March 16)

by neufer » Tue Mar 17, 2009 7:58 pm

neufer wrote:I can remember a sophomore year physics quiz question from M.I.T. (1964):

A rocket ship travels with velocity v (vis a vis the earth) in direction x.
The rocket ship sends a laser beam out the side of the ship in direction y.
What angle does the laser beam make with the y axis as observed from earth?

The teachers who posed this question got the answer wrong!
Pete wrote:
neufer wrote:
Pete wrote:sin theta = v_y / c.
Very good, Pete, you got their wrong answer with their wrong reasoning...so you got it right! :)
I'll take it! :) Okay, you went to MIT; what's the "right" answer? :D
--------------------------------------------------
  • A rocket ship travels with velocity v (vis a vis the earth) in direction x.

    The rocket ship sends a laser beam out the side of the ship in direction y;
    the rocket ship sends a stream of ping pong balls out the side of the ship in direction y;
    the rocket ship sticks a yardstick out the side of the ship in direction y.

    The laser beam, stream of ping pong balls & yardstick ALL DEFINE the y axis
    which is unaffected by motion in the direction x (except for translation)
    (Lorentz transformation ONLY affect the x axis & the time axis).

    Hence, the laser beam, stream of ping pong balls & yardstick are ALL
    unaffected by in both length & direction by the Lorentz transformation.
As for the individual photons of velocity c to
keep up with a rocket ship moving with velocity v
they must, indeed, (obviously) have an aberration of theta = arcsin(v/c)
such that [c sin(theta)] = v as you have correctly calculated.

You were simply confusing the aberration of individual photons with
the laser beam locked formation of those photons along the y axis.

(As I recall I failed to get either answer right at the time. :roll: )

Art Neuendorffer
  • As I was going to St Ives
    I met a man with seven wives

    And every wife had seven sacks
    And every sack had seven cats
    And every cat had seven kits

    Kits, cats, sacks, wives
    How many were going to St Ives?

Re: Interesting 'tease' ... Deimos (2009 March 16)

by Pete » Tue Mar 17, 2009 5:04 pm

neufer wrote:
Pete wrote:
neufer wrote:I can remember a sophomore year physics quiz question from M.I.T. (1964):

A rocket ship travels with velocity v (vis a vis the earth) in direction x.
The rocket ship sends a laser beam out the side of the ship in direction y.
What angle does the laser beam make with the y axis as observed from earth?

The teachers who posed this question got the answer wrong!
sin theta = v_y / c.
Very good, Pete, you got their wrong answer with their wrong reasoning...so you got it right! :)
I'll take it! :) Okay, you went to MIT; what's the "right" answer? :D

Re: Interesting 'tease' ... Deimos (2009 March 16)

by neufer » Tue Mar 17, 2009 4:14 am

Pete wrote:
neufer wrote:I can remember a sophomore year physics quiz question from M.I.T. (1964):

A rocket ship travels with velocity v (vis a vis the earth) in direction x.
The rocket ship sends a laser beam out the side of the ship in direction y.
What angle does the laser beam make with the y axis as observed from earth?

The teachers who posed this question got the answer wrong!
sin theta = v_y / c.
Very good, Pete, you got their wrong answer with their wrong reasoning...so you got it right! :)

Re: Interesting 'tease' ... Deimos (2009 March 16)

by Pete » Tue Mar 17, 2009 2:17 am

neufer wrote:I can remember a sophomore year physics quiz question from M.I.T. (1964):

A rocket ship travels with velocity v (vis a vis the earth) in direction x.
The rocket ship sends a laser beam out the side of the ship in direction y.
What angle does the laser beam make with the y axis as observed from earth?

The teachers who posed this question got the answer wrong!

The quiz was scored as follows:

1) If you got the right answer with the right (or no) reasoning you got it right.
2) If you got their wrong answer with their wrong reasoning you got it right
3) If you got their wrong answer using some other (or no) reasoning you got it wrong.
4) If you got the right answer with the wrong reasoning you got it wrong.

(So what is the right answer?)
Below, I mistyped "u" instead of "v," and since I'm short on time, let's say the rocket ship travels with velocity "u" relative to Earth. :)
Primed axes belong to the ship; unprimed axes belong to Earth.
The Lorentz transformation equations for motion along the x axis are
Image,

where
Image.

Taking differentials,
Image.

Dividing, we get the transformation equations for some speed v = (v_x, v_y):
Image

Solving for the speed as measured in Earth's frame,
Image

Now, in the spaceship's frame, the laser beam's velocity components are v_x' = 0, v_y' = c. Plug into the above to get
Image

Measure the angle theta from the x axis to the laser beam (in Earth's frame); sorry, no diagram. Then trigonometry gives
Image
...oops, where the above should read: sin theta = v_y / c.

Re: Deimos -- Not a moon ...

by BMAONE23 » Mon Mar 16, 2009 11:38 pm

I believe that, to be a moon,

has yet to be defined

But I believe that a captured comet or asteroid could be considered a moon if it is in orbit around a planet

This ought to muddy up any Moon definition

Re: Deimos -- Not a moon ...

by wannabeastro » Mon Mar 16, 2009 10:20 pm

i had wondered the same thing before, what makes Deimos or other such objects a moon. Most of them appear to be nothing more than asteroids. I thought maybe it was being caught in the planets orbit?

Re: Interesting 'tease' ... Deimos (2009 March 16)

by neufer » Mon Mar 16, 2009 10:10 pm

JohnD wrote:Phobos is markedly 'grooved', or has long, clear crater chains, depending on which church you belong to.
Deimos here looks as smoothly cheeked as a girl.

Is the photograph resolution enough to show up similar markings on Deimos?
Probably not: Mars Reconnaissance Orbiter gets 3.5 times closer
to Phobos (5700 km.) than it does to Deimos (19800 km.)

And Mars Global Surveyor has gotten as close as 1080 km. to Phobos (though, perhaps, with no better resolution).

Art Neuendorffer
-------------------------------------------------------
Note:
http://en.wikipedia.org/wiki/Phobos_(moon) wrote:Recent images from Mars Global Surveyor indicate that
Phobos is covered with a layer of fine-grained regolith at least 100 meters thick.
This should really be "at least 100 centimeters thick."
http://www.jpl.nasa.gov/news/releases/98/mgsphobos.html

Re: Interesting 'tease' ... Deimos (2009 March 16)

by JohnD » Mon Mar 16, 2009 9:02 pm

Phobos is markedly 'grooved', or has long, clear crater chains, depending on which church you belong to.
Deimos here looks as smoothly cheeked as a girl.

Is the photograph resolution enough to show up similar markings on Deimos?

John

Re: Deimos -- Not a moon ...

by neufer » Mon Mar 16, 2009 8:59 pm

DavidACaruso wrote:Re: APOD, March 16, 2009
Why call Deimos a moon? We usually think of moons as something spherical, and probably relatively significant in size. Common sense (which may be incorrect) tells us Deimos is an asteroid caught in Mars orbit. Following the logic of categorizing Deimos as a moon, then perhaps categorize even the smallest rocks that fit in your hand that orbit a planet as "moons". Deimos even looks like your stereotypical asteroid.
You may call them natural satellites if you prefer.
---------------------------------------------------------------
Satellite, n. [F., fr. L. Stelles, -itis, an attendant.]

1. An attendant attached to a prince or other powerful person; hence, an obsequious dependent.

2. (Astron.) A secondary planet which revolves about another planet; as, the moon is a satellite of the earth.
------------------------------------------------
"My little love apprencisses, my dears, the estelles, van Nessies" - Finnegans Wake page 365.28
.....................................................
"Stella" (Esther) Johnson (March 18, 1681 – January 28, 1728) was the English friend of Jonathan Swift. A curious collection of her witticisms was published by Swift under the titles of "Bon Mots de Stella" as an appendix to some editions of Gulliver's Travels.
.....................................................
"Vanessa" (Esther) Vanhomrigh(c. 1688 – 2 June 1723), an Irish woman of Dutch descent, was a longterm lover and correspondent of Jonathan Swift. Swift's letters to her were published after her death. She was fictionalized as "Vanessa" in Swift's poem Cadenus and Vanessa (1713).
---------------------------------------------------------------
http://en.wikipedia.org/wiki/Natural_satellite wrote:
<<A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called the primary. The first known natural satellite was the Moon (luna in Latin). Until the discovery of the Galilean satellites in 1610, however, there was no opportunity for referring to such objects as a class. Galileo chose to refer to his discoveries as Planetæ ("planets"), but later discoverers chose other terms to distinguish them from the objects they orbited.

Christiaan Huygens, the discoverer of Titan, was the first to use the term moon for such objects, calling Titan Luna Saturni or Luna Saturnia – "Saturn's moon" or "The Saturnian moon", because it stood in the same relation to Saturn as the Moon did to the Earth.

As additional moons of Saturn were discovered, however, this term was abandoned. Giovanni Domenico Cassini sometimes referred to his discoveries as planètes in French, but more often as satellites, using a term derived from the Latin satelles, meaning "guard", "attendant", or "companion", because the satellites accompanied their primary planet in their journey through the heavens.

The term satellite thus became the normal one for referring to an object orbiting a planet, as it avoided the ambiguity of "moon". In 1957, however, the launching of the artificial object Sputnik created a need for new terminology. The terms man-made satellite or artificial moon were very quickly abandoned in favor of the simpler satellite, and as a consequence, the term has come to be linked primarily with artificial objects flown in space – including, sometimes, even those which are not in orbit around a planet.

As a consequence of this shift in meaning, the term moon, which had continued to be used in a generic sense in works of popular science and in fiction, has regained respectability and is now used interchangeably with satellite, even in scientific articles. When it is necessary to avoid both the ambiguity of confusion with the Earth's moon on the one hand, and artificial satellites on the other, the term natural satellite (using "natural" in a sense opposed to "artificial") is used.

There is no established lower limit on what should be considered a moon. Every body with an identified orbit, some as small as a kilometer across, has been identified as a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets. Small asteroid moons, such as Dactyl, have also been called moonlets.

The upper limit is also vague. When the masses of two orbiting bodies are similar enough that one cannot be said to orbit the other, they are described as a double body rather than primary and satellite. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition as to what constitutes a moon. Some authors consider the Pluto-Charon system to be a double (dwarf) planet. The most common dividing line on what is considered a moon rests upon whether the barycentre is below the surface of the larger body, though this is somewhat arbitrary, as it relies on distance as well as relative mass.

As of September 2008, 335 bodies are formally classified as moons. They include 167 orbiting six of the eight planets, 6 orbiting three of the five dwarf planets, 104 asteroid moons, and 58 satellites of Trans-Neptunian objects, some of which will likely turn out to be dwarf planets. Some 150 additional small bodies were observed within Saturn's ring system, but they were not tracked long enough to establish orbits. Other stars and their planets are likely to have natural satellites as well, although none have been observed.>>

Deimos -- Not a moon ...

by DavidACaruso » Mon Mar 16, 2009 8:22 pm

Re: APOD, March 16, 2009

Why call Deimos a moon? We usually think of moons as something spherical, and probably relatively significant in size. Common sense (which may be incorrect) tells us Deimos is an asteroid caught in Mars orbit. Following the logic of categorizing Deimos as a moon, then perhaps categorize even the smallest rocks that fit in your hand that orbit a planet as "moons". Deimos even looks like your stereotypical asteroid.

Re: Interesting 'tease'.....

by aristarchusinexile » Mon Mar 16, 2009 5:01 pm

orin stepanek wrote: The moon looks almost like it's made of glass. Or is that just a product of the photography used? Orin
Excellent Wiki article on Diemos including animation of the orbits of Phobos and Diemos around Mars.
http://en.wikipedia.org/wiki/Deimos_(moon)

Re: Deimos (2009 March 16)

by aristarchusinexile » Mon Mar 16, 2009 4:54 pm

watch24 wrote: Thing is, these guys were no dumber than we are--maybe smarter in terms of deductive reasoning, but they were blinded to new truth by intellectual pride and arrogance. Surely none of this goes on in today's scientific community! And most assuredly no scientific conclusions are influenced by recognition, acceptance, or grant money! :wink:
... or the green eyed god Consensus.

Titus/Bode : Fibonacci assumption?

by neufer » Mon Mar 16, 2009 4:49 pm

bystander wrote:See the 16Mar09 APOD link Kepler's prediction. It means Altissimum planetam tergeminum observavi.
http://en.wikipedia.org/wiki/Moons_of_Mars wrote: <<The astronomer Johannes Kepler (1571-1630) even predicted their number correctly, although with faulty logic:
he wrote that since Jupiter had four known moons and Earth had one, it was only natural that Mars should have two.

Perhaps inspired by Kepler, Jonathan Swift's novel Gulliver's Travels (1726) refers to two moons in part 3, chapter 3 (the "Voyage to Laputa"), in which the astronomers of Laputa are described as having discovered two satellites of Mars orbiting at distances of 3 and 5 Martian diameters, and periods of 10 and 21.5 hours, respectively.

Code: Select all

"Titus/Bode : Fibonacci assumption?"

Fibonacci
Jupiter
diameters  km.   actual
--------------------------------------
_3  __415,038  __421,700   Io
_5  __691,730  __671,034   Europa
_8  1,106,768  1,070,412   Ganymede
13  1,798,498  1,882,709   Callisto
-----------------------------------------
[/b]
  • They [the Laputan astronomers] have likewise discovered two lesser stars, or 'satellites', which revolve about Mars, whereof the innermost is distant from the centre of the primary planet exactly three of his diameters, and the outermost five; the former revolves in the space of ten hours, and the latter in twenty-one and a half; so that the squares of their periodical times are very near in the same proportion with the cubes of their distance from the centre of Mars, which evidently shows them to be governed by the same law of gravitation, that influences the other heavenly bodies...
Phobos and Deimos are in fact about 1.4 and 3.5 diameters from Mars' centre, and their periods are 7.7 and 30.3 hours, respectively. A similar discovery was described by Voltaire in his interplanetary romance Micromegas, published in 1752.

In recognition of these 'predictions', two craters on Deimos are named Swift and Voltaire.
Image>>
--------------------------------------
Laputan astronomer Art Neuendorffer (retired) :wink:

Re: Interesting 'tease' ... Deimos (2009 March 16)

by Indigo_Sunrise » Mon Mar 16, 2009 3:57 pm

Thank you, bystander, for your helpful reply. (And for editing my post & title for clarity. At least, I'll guess that you were the one that edited it....)
But anyway, I hadn't had time to follow all the links in the description and the direct link you provided was very interesting.
Galileo was one multi-faceted guy! 8)

Re: Deimos-March 16 APOD

by neufer » Mon Mar 16, 2009 3:37 pm

watch24 wrote:I found the hyperlink for 'Kepler's prediction' particularly interesting. I'd heard that the moons were predicted long before they were actually discovered but was disappointed to find out why--and I always thought so much of Kepler!
Kepler provided testable hypotheses based upon the assumption
that the real world was best explained by elegant mathematics.

Some of his hypotheses panned out while others didn't.

(A few were apparently just lucky guesses.)
---------------------------------------------------------------------------
I can remember a sophomore year physics quiz question from M.I.T. (1964):
  • A rocket ship travels with velocity v (vis a vis the earth) in direction x.
    The rocket ship sends a laser beam out the side of the ship in direction y.
    What angle does the laser beam make with the y axis as observed from earth?
The teachers who posed this question got the answer wrong!

The quiz was scored as follows:
  • 1) If you got the right answer with the right (or no) reasoning you got it right.
    2) If you got their wrong answer with their wrong reasoning you got it right
    3) If you got their wrong answer using some other (or no) reasoning you got it wrong.
    4) If you got the right answer with the wrong reasoning you got it wrong.
(So what is the right answer?)

Kepler got his right answer (2 moons) with the wrong reasoning...so he got it wrong.

Re: Interesting 'tease'.....

by bystander » Mon Mar 16, 2009 3:19 pm

Indigo_Sunrise wrote: smaismrmilmepoetaleumibunenugttauiras ?????????

I saw this 'wording' listed as "Tomorrow's Image" for Sunday's APoD, 15Mar09, but was not able to figure out what it meant/stood for then, or now - even after seeing the image for today. Anybody able to translate?
See the 16Mar09 APOD link Kepler's prediction. It means Altissimum planetam tergeminum observavi.

Re: Interesting 'tease'.....

by neufer » Mon Mar 16, 2009 2:59 pm

orin stepanek wrote: http://apod.nasa.gov/apod/ap090316.html
The moon looks almost like it's made of glass.
Reminds me of an unripe strawberry (Fragaria Rosaceae):
Image

Fra. Rosacea. Blinis
Alcofribas Nasier

Deimos (2009 March 16)

by watch24 » Mon Mar 16, 2009 2:49 pm

I found the hyperlink for 'Kepler's prediction' particularly interesting. I'd heard that the moons were predicted long before they were actually discovered but was disappointed to find out why--and I always thought so much of Kepler! The real punch line is at the end of the story where the Aristotelian establishment refused to even view Galileo's discoveries through his scope because they didn't want to see physical appearances that conflicted with their tightly-held conclusions.

Thing is, these guys were no dumber than we are--maybe smarter in terms of deductive reasoning, but they were blinded to new truth by intellectual pride and arrogance. Surely none of this goes on in today's scientific community! And most assuredly no scientific conclusions are influenced by recognition, acceptance, or grant money! :wink:

Re: Interesting 'tease'.....

by orin stepanek » Mon Mar 16, 2009 12:55 pm

Indigo_Sunrise wrote: smaismrmilmepoetaleumibunenugttauiras ?????????

I saw this 'wording' listed as "Tomorrow's Image" for Sunday's APoD, 15Mar09, but was not able to figure out what it meant/stood for then, or now - even after seeing the image for today. Anybody able to translate?

Thank in advance! :mrgreen:
Eventually It became this: http://apod.nasa.gov/apod/ap090316.html :lol: I saw it also last night! Maybe a cat walked across the keyboard. :shock:

The moon looks almost like it's made of glass. Or is that just a product of the photography used?

Orin

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