Dodgy astronomy on TV - for amusement only

On or about 2005-02-13,
Stephen Tonkin illuminated us with:
Mark Ayliffe wrote:
I think the best answer is that the moon doesn't have a year.

Whether or not it is the "best" answer (I guess that depends on your
definition of "best"), it is the wrong answer, for the simple reason
that the Moon does have a year (unless, of course, you are using some
strange definition of "year" of which astronomers are not yet aware).

Could you supply a link to somewhere so that I can understand that better
please? I did spend some time looking around various usually authoritative
resources before posting that.

--
Mark
Real email address | Timing has an awful lot to do with
is mark at | the outcome of a rain dance.
ayliffe dot org |

Was Dodgy astronomy on TV - for amusement only

Stephen Tonkin wrote:

In the case of the Earth this is 24hours (all figures rounded)

Yes, for a *mean* solar day. A sidereal day is a tad shorter.

Any non-astronomer is likely to assume that a single rotation means
360 degrees.

Astronomers always prefer confusion and go straight to sidereal days
or rotation with respect to the stars. Why not make it easy by saying
a sidereal day is 360 degrees? The next step to a solar day of close
to 361 deg then becomes much easier to understand.

I saw the light of understanding in a class of kids the other day when
I got them to think about a bike wheel doing a single rotation first
on a flat road and then over the crown of a hill. Having a bike wheel
in my hand helped...

Is there a pool of shared ideas anywhere of ways that work for
explaining basic astronomy to newbies/children?

Watching teachers covering astronomy for GCSE is generally painful and
half the books I read seem designed to spread confusion.

Cheers

Martin

--
Martin Frey
http://www.hadastro.org.uk
N 51 02 E 0 47

"Mark Ayliffe" wrote in message
...
| On or about 2005-02-13,
| Stephen Tonkin illuminated us with:
| Mark Ayliffe wrote:
| I think the best answer is that the moon doesn't have a year.
|
| Whether or not it is the "best" answer (I guess that depends on your
| definition of "best"), it is the wrong answer, for the simple reason
| that the Moon does have a year (unless, of course, you are using some
| strange definition of "year" of which astronomers are not yet aware).
|
| Could you supply a link to somewhere so that I can understand that better
| please? I did spend some time looking around various usually authoritative
| resources before posting that.
|

The moon's year is the same as the earth's.

Imagine looking down on the earth-moon system from well above one of the
earth's poles. Which way is the moon travelling? Relative to the sun,
*always in the same direction the earth is*.

Don't believe me? Then answer these questions:

1) What is the earth's orbital velocity around the sun?

2) What is the escape velocity from earth?

The answer to (2) is less than the answer to (1) which means the moon cannot
be doing circles round us as some people think. Both bodies always orbit
the sun in the same direction but traversing intersecting curves varying
either side of the orbit traced by the earth/moon system's centre of mass.
The earth is much heavier than the moon so deviates relatively little (a few
thousand miles) from side to side of that orbit. The lighter moon swings
about 250 000 miles either side. It travels faster than we do when "full"
and thus overtaking us, and slower than we do when "new" and we are
overtaking it, but if we are orbiting at 18 miles/ second, the moon must
even at "new" be travelling faster than 11 miles / second or we would be
waving it "goodbye", escape velocity from the system being rather less than
7 miles/second at the moon's distance.

If you look at the whole thing to scale the paths of the two bodies are
almost indistinguishable, so how can you say that one has a "year" and the
other doesn't?

In fact, because Earth is so close to the Sun and so small, it is impossible
for *any* satellite, natural or artificial, to circle us with regard to the
reference frame of the sun. An equatorial satellite will take our path but
with a distorted sine wave modulation (the "trough" on the sunward side
being sharper than the "crest" away from the sun). A polar orbiting
satellite traces a more complex orbit, varying between a helix of which the
earth's orbit is the axis and a sinusoidal modulation at the same angle to
the orbital plane as the inclination of the poles. Perhaps this is why an
astronaut who spends that period of time in the International Space Station
which is equivalent to just over 365 revolutions of the earth on its axis
(wrt the Sun) is still said to have spent "a year" there.
--
- Yokel -
oo oo
OOO OOO
OO 0 OO
) ( I ) (
) ( /\ ) (

"Yokel" now posts via a spam-trap account.
Replace my alias with stevejudd to reply.

JRS: In article , dated Wed, 16 Feb
2005 00:32:02, seen in news:uk.sci.astronomy, Yokel
posted :
The moon's year is the same as the earth's.

Imagine looking down on the earth-moon system from well above one of the
earth's poles. Which way is the moon travelling? Relative to the sun,
*always in the same direction the earth is*.

Don't believe me? Then answer these questions:

1) What is the earth's orbital velocity around the sun?

2) What is the escape velocity from earth?

The answer to (2) is less than the answer to (1) which means the moon cannot
be doing circles round us as some people think.

Your (2) is irrelevant.

If the Earth were to be shrunk, preserving its mass, the Moon's
behaviour would scarcely be affected, and both would follow their
present paths. But the Earth's escape velocity would increase until it
reached c and the Earth vanished within its own Schwarzschild radius, or
whatever.

It is because the moon's orbital speed is less than the earth's that the
moon's path does not cross itself (in plan view, disregarding tilts &
details). Even LEO satellites do not have self-crossing paths.

And because the gravitational field of the Sun at the Moon is less (by a
modest factor) than that of the Earth at the Moon, the Moon's path is
always concave towards the Sun - like a cross between a 3d bit and a 50p
piece.

URL:http://www.merlyn.demon.co.uk/gravity2.htm#Moon

--
© John Stockton, Surrey, UK. Turnpike v4.00 MIME. ©
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
some Astro stuff via astro.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

Martin Frey wrote:
Was Dodgy astronomy on TV - for amusement only

Stephen Tonkin wrote:

In the case of the Earth this is 24hours (all figures
rounded)

Yes, for a *mean* solar day. A sidereal day is a tad shorter.

Any non-astronomer is likely to assume that a single rotation means
360 degrees.

Astronomers always prefer confusion and go straight to sidereal days
or rotation with respect to the stars. Why not make it easy by saying
a sidereal day is 360 degrees? The next step to a solar day of close
to 361 deg then becomes much easier to understand.

I saw the light of understanding in a class of kids the other day
when
I got them to think about a bike wheel doing a single rotation first
on a flat road and then over the crown of a hill. Having a bike wheel
in my hand helped...

Is there a pool of shared ideas anywhere of ways that work for
explaining basic astronomy to newbies/children?

Watching teachers covering astronomy for GCSE is generally painful
and
half the books I read seem designed to spread confusion.

Cheers

Martin

--
Martin Frey
http://www.hadastro.org.uk
N 51 02 E 0 47

It is stomachturning to know that you are teaching kids,given that it
will certainly weaken kids understanding of astronomy and the
principles which constitute the equable day,clocks, the geometry of the
Earth ect ,I'm sure no parent who endeavor to call themselves parents
would put their kids intentionally in harms way and leave them to
'teachers' like you.The basic human instinct is to protect children but
you intellectual weaklings have managed to overide that fundamental
instinct.


You silly ****er are teaching kids that the Earth's axial and orbital
motion is a single sidereal motion when in fact they are independent of
each other.

Maybe your nation is getting what it deserves,by not recognising how
John Harrison worked on the principle of the 24 hour/360 deg
equivalency via the Equation of Time correction and opting for
Flamsteed's erroneous isochronical sidereal 'proof' you will eventually
turn your nation into a bunch of imbeciles.

You should'nt be near children especially when a half wit could tell
you that the longitude co-ordinates you give in your signature also
represent a specific 'time' value of a 24 hour clock allied to axial
rotation through 360 degrees.

Again,maybe your nation is getting what it desrves.

In article . com,
burbled happily...

You should'nt be near children especially when a half wit could tell
you that the longitude co-ordinates you give in your signature also
represent a specific 'time' value of a 24 hour clock allied to axial
rotation through 360 degrees.

And that's precisely what you're doing.

Again,maybe your nation is getting what it desrves.

Does this make some sort of sense on your planet?
--
Craig Oldfield

On 20 Feb 2005 06:04:02 -0800, wrote:

You should'nt be near...

Isn't the apostrophe in the wrong place here? I think it should be
between the "n" and the "t". I believe it represents a missing letter
for example "n't" could be taken to mean "nut".

--
Pete
http://www.digitalsky.org.uk
Global Projects - http://www.globalobservers.net

In message . com,
writes

Martin Frey wrote:
Was Dodgy astronomy on TV - for amusement only

Stephen Tonkin wrote:

In the case of the Earth this is 24hours (all figures
rounded)

Yes, for a *mean* solar day. A sidereal day is a tad shorter.

Any non-astronomer is likely to assume that a single rotation means
360 degrees.

Astronomers always prefer confusion and go straight to sidereal days
or rotation with respect to the stars. Why not make it easy by saying
a sidereal day is 360 degrees? The next step to a solar day of close
to 361 deg then becomes much easier to understand.

I saw the light of understanding in a class of kids the other day
when
I got them to think about a bike wheel doing a single rotation first
on a flat road and then over the crown of a hill. Having a bike wheel
in my hand helped...

Is there a pool of shared ideas anywhere of ways that work for
explaining basic astronomy to newbies/children?

Watching teachers covering astronomy for GCSE is generally painful
and
half the books I read seem designed to spread confusion.

Cheers

Martin

--
Martin Frey
http://www.hadastro.org.uk
N 51 02 E 0 47

It is stomachturning to know that you are teaching kids,given that it
will certainly weaken kids understanding of astronomy and the
principles which constitute the equable day,clocks, the geometry of the
Earth ect ,I'm sure no parent who endeavor to call themselves parents
would put their kids intentionally in harms way and leave them to
'teachers' like you.The basic human instinct is to protect children but
you intellectual weaklings have managed to overide that fundamental
instinct.


You silly ****er are teaching kids that the Earth's axial and orbital
motion is a single sidereal motion when in fact they are independent of
each other.

Is that supposed to mean something, you foul-mouthed little idiot?
Don't forget that abusive language can result in a report to your ISP.
Of course the axial and orbital motions are independent, except that
orbital motion results in a difference between a complete rotation
relative to the stars and one relative to the sun.


Maybe your nation is getting what it deserves,by not recognising how
John Harrison worked on the principle of the 24 hour/360 deg
equivalency via the Equation of Time correction and opting for
Flamsteed's erroneous isochronical sidereal 'proof' you will eventually
turn your nation into a bunch of imbeciles.

Do you really understand what the Equation of Time does? It expresses
the difference between the day length as measured by the sun, and the
civil day of 24 hours of equal length, convenient for human activity.


You should'nt be near children especially when a half wit could tell
you that the longitude co-ordinates you give in your signature also
represent a specific 'time' value of a 24 hour clock allied to axial
rotation through 360 degrees.

Actually, the Earth rotates through 360 degrees relative to the stars in
23 hours 56 minutes.
--
Support the DEC Tsunami Appeal http://www.dec.org.uk/.
Remove spam and invalid from address to reply.

"Pete Lawrence" wrote in message
...
On 20 Feb 2005 06:04:02 -0800, wrote:

You should'nt be near...

Isn't the apostrophe in the wrong place here? I think it should be
between the "n" and the "t". I believe it represents a missing letter
for example "n't" could be taken to mean "nut".

*Could* be taken to mean "nut"? I do not think there is much doubt in this
case.

;-)

Chuck Taylor
Do you observe the moon?
Try http://groups.yahoo.com/group/lunar-observing/

Are you interested in understanding optics?
Try http://groups.yahoo.com/group/ATM_Optics_Software/

************************************

--
Pete
http://www.digitalsky.org.uk
Global Projects - http://www.globalobservers.net

Hi all

In the Magic Roundabout movie there's a scene, where the heroes are in a hot
air balloon, where the Moon is back-to-front.

Neil