OT impending lunar eclipse and ABQ

[Frank]

http://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2009Aug06N.pdf

I'd like to use C to calculate whether I will be able to see the lunar
eclipse tomorrow. The calculations are usually trivial once one
understands the ephemera in his own frame of reference.

I hope James Kuyper is here today. Can anyone tell me the physical
significance of P1 and P4?

 

[Frank]

Frank said:



#include <stdio.h>

int main(void)
{
  puts("If you're in Grand Rapids, Michigan, you'll");
  puts("be able to see the lunar eclipse of 6 August");
  puts("2009 at moonrise.");
  return 0;

}

The above C program amply demonstrates the triviality of such
calculations.


They are the leading and trailing edges of the penumbra.

ok I get it now. you're a lucky son of a country, heathfield; this
thing is right on top of you at dusk tomorrow. some integer plus or
minus 2:14

 

[Keith Thompson]

Frank said:

http://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2009Aug06N.pdf [...]
I  hope James Kuyper is here today.  Can anyone tell me the physical
significance of P1 and P4?

They are the leading and trailing edges of the penumbra.

ok I get it now. you're a lucky son of a country, heathfield; this
thing is right on top of you at dusk tomorrow. some integer plus or
minus 2:14

<OT>
But it's not going to be all that impressive. It's just a penumbral
eclipse. At its greatest extent about half the Moon will be
*slightly* shaded, and about half will be in full sunlight.
</OT>

 

[Frank]

Frank said:
http://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2009Aug06N.pdf [...]
I  hope James Kuyper is here today.  Can anyone tell me the physical
significance of P1 and P4?
They are the leading and trailing edges of the penumbra.

ok I get it now.  you're a lucky son of a country, heathfield; this
thing is right on top of you at dusk tomorrow.  some integer plus or
minus 2:14

<OT>
But it's not going to be all that impressive.  It's just a penumbral
eclipse.  At its greatest extent about half the Moon will be
*slightly* shaded, and about half will be in full sunlight.
</OT>

I've got an estimate for the length of it now:


F:\gfortran\dan>type eclipse1.f90


implicit integer (a-k)

real proportion, tja

proportion = .1

tja = 66 * sin(proportion)

print *, "Number of minutes moon is occluded", tja

end program

! gfortran eclipse1.f90 -o e.exe
F:\gfortran\dan>e
Number of minutes moon is occluded 6.5890055

F:\gfortran\dan>

Fortran is a common C extension, and I think we revert to our more
comfortable languages when we have something quick and dirty to
calculate.

By comparison, Keith, you have the booby prize, slightly unable to see
this occlusion. It's a pretty good game when the losing scenario
reveals a perfect and full moon. I'll be out in Moriarty, New Mexico,
with my telescope

 

[user923005]

http://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2009Aug06N.pdf

I'd like to use C to calculate whether I will be able to see the lunar
eclipse tomorrow.  The calculations are usually trivial once one
understands the ephemera in his own frame of reference.

I  hope James Kuyper is here today.  Can anyone tell me the physical
significance of P1 and P4?

This turned up a jillion hits:
http://www.google.com/search?source...US280&q=calculate++"lunar+eclipse"+C+"Math.h"

OK, only 218. But I bet one of them has what you want.

 

[James Dow Allen]

I'd like to use C to calculate whether I will be able to see the lunar
eclipse tomorrow.

What *I* want to know is: what are the odds I will be
still alive in time to see Betelgeuse go supernova?

 

[James Kuyper]

http://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2009Aug06N.pdf

I'd like to use C to calculate whether I will be able to see the lunar
eclipse tomorrow. The calculations are usually trivial once one
understands the ephemera in his own frame of reference.

I hope James Kuyper is here today. ...

I am. Unfortunately, I have no such program already written. I do know
enough to set up the calculations and write such a program, but I have
nowhere near enough free time to do so in time for the eclipse (the way
my life is going, I doubt that I will have enough free time any time
this year).

Why bother? That map should answer your question well enough.

Can anyone tell me the physical
significance of P1 and P4?

P1 and P4, as indicated in the top diagram, are the times at which the
Moon enters and exits the Earth's penumbra. The curves on the map
labeled P1 and P4 are the places on earth where the Moon will be just
barely visible on the horizon (assuming clear skies) at those times. To
a very good approximation, those curves move due west at a constant
angular rate, so you can estimate how much of the eclipse you will see,
and when, just by measuring the horizontal distance from your location
on the map to the P1 and P4 curves.

 

[Frank]

I am. Unfortunately, I have no such program already written. I do know
enough to set up the calculations and write such a program, but I have
nowhere near enough free time to do so in time for the eclipse (the way
my life is going, I doubt that I will have enough free time any time
this year).

Why bother? That map should answer your question well enough.


P1 and P4, as indicated in the top diagram, are the times at which the
Moon enters and exits the Earth's penumbra. The curves on the map
labeled P1 and P4 are the places on earth where the Moon will be just
barely visible on the horizon (assuming clear skies) at those times. To
a very good approximation, those curves move due west at a constant
angular rate, so you can estimate how much of the eclipse you will see,
and when, just by measuring the horizontal distance from your location
on the map to the P1 and P4 curves.

thx james. The full eclipse lasts 66 seconds. I decided that the
amount you would see, if you are in the region between P1 and P4 is
described by the curved line that would intersect P1 and P4 normally
and go through where I set up my telescope, which is near Abq. You
map it onto the unit interval, such that P1 lands on zero and P4 lands
on one. Then there exists a point on the same metric that intersects
abq

tja = 66 * sin(proportion)

 

[Antoninus Twink]

puts("If you're in Grand Rapids, Michigan, you'll");
puts("be able to see the lunar eclipse of 6 August");
puts("2009 at moonrise.");

Typically useless answer, and typically poor Heathfield code.

Why suffer the overhead of three separate function calls, when even the
20-year old C standard that you insist on clinging to guarantees support
for strings of length up to 509 characters?

 

[Keith Thompson]

thx james. The full eclipse lasts 66 seconds.

The penumbral eclipse lasts over 3 hours. I see the
[DELTA] T = 66s
in the document, but that's just the difference between GMT (based on
the Earth's rotation) and TDT (atomic time); see

I decided that the
amount you would see, if you are in the region between P1 and P4 is
described by the curved line that would intersect P1 and P4 normally
and go through where I set up my telescope, which is near Abq.

If Abq is Albuquerque, I don't think you're going to see much. By the
time the Moon rises in your location, the eclipse will be almost over.
Most of the Moon will be fully illuminated by sunlight; a little bit
of the southwest edge will be in partial shade. If you were standing
on that part of the Moon during the eclipse, you'd see most of the Sun
peeking out from behind Earth. It's certainly worth taking a look,
but I think it will be a challenge to see any difference from an
ordinary full Moon. You might see a bit of a reddish tinge.

You
map it onto the unit interval, such that P1 lands on zero and P4 lands
on one. Then there exists a point on the same metric that intersects
abq

tja = 66 * sin(proportion)

What is "tja"?

 

[Frank]

[...]

thx james.  The full eclipse lasts 66 seconds.

The penumbral eclipse lasts over 3 hours.  I see the
    [DELTA] T = 66s
in the document, but that's just the difference between GMT (based on
the Earth's rotation) and TDT (atomic time); see

                                                I decided that the
amount you would see, if you are in the region between P1 and P4 is
described by the curved line that would intersect P1 and P4 normally
and go through where I set up my telescope, which is near Abq.

If Abq is Albuquerque, I don't think you're going to see much.  By the
time the Moon rises in your location, the eclipse will be almost over.
Most of the Moon will be fully illuminated by sunlight; a little bit
of the southwest edge will be in partial shade.  If you were standing
on that part of the Moon during the eclipse, you'd see most of the Sun
peeking out from behind Earth.  It's certainly worth taking a look,
but I think it will be a challenge to see any difference from an
ordinary full Moon.  You might see a bit of a reddish tinge.

Heathfield could be looking at it right now. Alright so my delta t is
physically meaningless. I guess the time that anyone in the states in
the P1-P4 range observes the moon after moonrise until 8:14 mountain
is the length of the eclipse. I think that's sixteen minutes for me,
which is a lot better than 6.58 seconds.
http://www.timeanddate.com/worldclock/astronomy.html?obj=moon&n=394

What is "tja"?

Tja is an appropriate word for when you calculate something physically
meaningless and publish it on the web. Tja.

 

[Keith Thompson]

[...]

thx james.  The full eclipse lasts 66 seconds.

The penumbral eclipse lasts over 3 hours.  I see the
    [DELTA] T = 66s
in the document, but that's just the difference between GMT (based on
the Earth's rotation) and TDT (atomic time); see

                                                I decided that the
amount you would see, if you are in the region between P1 and P4 is
described by the curved line that would intersect P1 and P4 normally
and go through where I set up my telescope, which is near Abq.

If Abq is Albuquerque, I don't think you're going to see much.  By the
time the Moon rises in your location, the eclipse will be almost over.
Most of the Moon will be fully illuminated by sunlight; a little bit
of the southwest edge will be in partial shade.  If you were standing
on that part of the Moon during the eclipse, you'd see most of the Sun
peeking out from behind Earth.  It's certainly worth taking a look,
but I think it will be a challenge to see any difference from an
ordinary full Moon.  You might see a bit of a reddish tinge.

Heathfield could be looking at it right now.

No, he couldn't, since it hasn't started yet. The start of the
eclipse is at 23:01:04 UTC, which is more than an hour and a half from
now. Lunar eclipses don't occur at different times in different
places. What you're seeing is an actual shadow on the Moon. Where
you are affects whether you can see it, not when. Solar eclipses, on
the other hand, depend on the spatial relationship among the Moon, the
Sun, and the observer, so they do occur at different times for
different observers.

(Actually, the location of the observer has a very small effect on
what parts of the Moon can be seen, but it's not detectable to the
eye.)

BTW, <http://en.wikipedia.org/wiki/August_2009_lunar_eclipse> says:

A penumbral lunar eclipse will take place on August 6, 2009, the
third of four lunar eclipses in 2009. The moon's small entry into
the earth's penumbral shadow will produce an extremely subtle
dimming of the moon's southern edge, difficult to observe
visually.

(August 6 is when the maximum occurs; the start of the eclipse is late
on August 5.)

[snip]

 

[Frank]

[...]
thx james.  The full eclipse lasts 66 seconds.
The penumbral eclipse lasts over 3 hours.  I see the
    [DELTA] T = 66s
in the document, but that's just the difference between GMT (based on
the Earth's rotation) and TDT (atomic time); see
<http://www.hermetic.ch/lcef/lcef_doc.htm#delta_t>.
                                                I decided that the
amount you would see, if you are in the region between P1 and P4 is
described by the curved line that would intersect P1 and P4 normally
and go through where I set up my telescope, which is near Abq.
If Abq is Albuquerque, I don't think you're going to see much.  By the
time the Moon rises in your location, the eclipse will be almost over.
Most of the Moon will be fully illuminated by sunlight; a little bit
of the southwest edge will be in partial shade.  If you were standing
on that part of the Moon during the eclipse, you'd see most of the Sun
peeking out from behind Earth.  It's certainly worth taking a look,
but I think it will be a challenge to see any difference from an
ordinary full Moon.  You might see a bit of a reddish tinge.

Heathfield could be looking at it right now.

No, he couldn't, since it hasn't started yet.  The start of the
eclipse is at 23:01:04 UTC, which is more than an hour and a half from
now.  Lunar eclipses don't occur at different times in different
places.  What you're seeing is an actual shadow on the Moon.  Where
you are affects whether you can see it, not when.  Solar eclipses, on
the other hand, depend on the spatial relationship among the Moon, the
Sun, and the observer, so they do occur at different times for
different observers.

(Actually, the location of the observer has a very small effect on
what parts of the Moon can be seen, but it's not detectable to the
eye.)

BTW, <http://en.wikipedia.org/wiki/August_2009_lunar_eclipse> says:

    A penumbral lunar eclipse will take place on August 6, 2009, the
    third of four lunar eclipses in 2009. The moon's small entry into
    the earth's penumbral shadow will produce an extremely subtle
    dimming of the moon's southern edge, difficult to observe
    visually.

(August 6 is when the maximum occurs; the start of the eclipse is late
on August 5.)

ok This is a strange thing to get ones head around. Luckily it
doesn't depend on my calculations. My gf and I have a motel in
Moriarty, NM, which is one of the clearest places to skywatch on this
planet. The radar looks clear.

I don't know how long moonrise takes, but I'll know a lot more later
today. out the door

 

[James Kuyper]

Frank wrote:
....

ok This is a strange thing to get ones head around. Luckily it
doesn't depend on my calculations. My gf and I have a motel in
Moriarty, NM, which is one of the clearest places to skywatch on this
planet. The radar looks clear.

I don't know how long moonrise takes, but I'll know a lot more later
today. out the door

Don't expect much; judging from that map, in New Mexico moonrise is
going to pretty much coincide with the end of the eclipse. Partial
eclipses are not very impressive even at the darkest point of the
eclipse, and what you'll see will be pretty much indistinguishable from
an ordinary full moon. If even part of the Earth's Umbra was going to
touch the Moon, the eclipse would be significantly more impressive, but
it's not coming close to the Umbra.

 

[Nick Keighley]

What *I* want to know is: what are the odds I will be
still alive in time to see Betelgeuse go supernova?

and apparently we are likely to survive it. it should be as bright
as a full moon.

 

[Richard Bos]

What is "tja"?

It is a Dutch word (or non-word, really) which the recurring kook and/or
troll Merrill&Michelle (a.k.a. Wade Ward, George, Frank and several
others) habitually misuses, relying on c.l.c'ers atrocious mid-term
memory to keep pulling replies.

Richard

 

[Frank]

Frank wrote:

...



Don't expect much; judging from that map, in New Mexico moonrise is
going to pretty much coincide with the end of the eclipse. Partial
eclipses are not very impressive even at the darkest point of the
eclipse, and what you'll see will be pretty much indistinguishable from
an ordinary full moon. If even part of the Earth's Umbra was going to
touch the Moon, the eclipse would be significantly more impressive, but
it's not coming close to the Umbra.

It was fun to make an event out of something that was perilously close
to being a non-event. It took till 8:06 for me to see the moon. I
guess I wasn't expecting it so far south, but it certainly rose where
predicted with a declination of -19 degrees. I wonder if there's a
convention for determining what counts as moonrise (leading edge,
trailing edge)

By 8:08 I had the telescope focused on it. All that was left was a
red hue on the bottom which is reversed in the scope. The whole thing
was then officially done at 8:14. It was a bit like snipe hunting but
great fun.

As for what I was calculating, I'm not sure that I have data enough to
determine how long the eclipse lasts at a given point. Tja.

 

[Frank]

It is a Dutch word (or non-word, really) which the recurring kook and/or
troll Merrill&Michelle (a.k.a. Wade Ward, George, Frank and several
others) habitually misuses, relying on c.l.c'ers atrocious mid-term
memory to keep pulling replies.

Richard

Again we have this dyspectic, dutch turd to remind why usenet isn't
worth the price of a newsfeed. His name means Dick Evil, and I
suspect he lives under the bridges of Amsterdam, throwing his poop at
people. I've never disliked a Hollander I've met in real life and
never liked a Hollander that I liked on the net.

 

[user923005]

With my luck, if it were to happen during my lifetime, it would probably be
while the full moon were at "perigeuse" during a cloudy night, with the
opposite side of the Earth facing it.

On the other hand, imagine a cloudless, moonless night, and you just happen
to be looking a Orion when the first light hits Earth.

I guess that it would scare the wee out of me.

 

[Sjouke Burry]

Frank said:



This would appear not to be true. Bos, it seems, translates as
"bunch".

<snip>

A "bos" is a big area planted with trees(in the Netherlands).