Hi all,

A few days ago I happened across an essay by the late Stephen Jay Gould
describing his observations of "ordinary New Yorkers" observing a near
total solar eclipse visible from that city (some decades ago). This
reminded me of a question that I had been meaning to ask here for
several months, but hadn't gotten around to. Here it is:

On 8 April 2005, it seems that a complete or nearly complete solar
eclipse should be visible from the Pitcairn Islands, with closest
approach to totality occurring at 11:49 AM local time, at an elevation
of about 55 degrees from the horizon. The same eclipse should in
principle be marginally visible near Balboa, Panama, with closest
approach to totality occuring at 5:13 PM local time--- but of course,
too low in the sky, arghghgh, to be really suitable for observation. An
interesting feature of this eclipse is that Venus should be visible only
two degrees away, which should further add to the drama of the event.
Are these predictions correct?

On 3 November 2005, it seems that a complete or nearly complete solar
eclipse should be visible near Avila, Spain, with closest approach to
totality occuring at 10:58 AM local time. Is this prediction correct?
Will these in fact be -complete- solar eclipses?

I also have two postdictions concerning historical events which I don't
have enough historical information to verify myself.

On 21 September 1922, according to Misner, Thorne, & Wheeler,
Gravitation, 1973 (this just happened to be the only book I had at hand
which contains any information at all about historical eclipses!), a
total solar eclipse was visible in Western Australia. Indeed, it seems
that the closest approach to totality, as seen from the vicinity of
Alice Springs, would have occured at 3:25 PM local time. Is this
correct?

On 8 April 2005, as we probably all remember, there occured a transit of
Venus across the visible solar disk. It seems that, weather permitting,
this would have been visible from the island of Diego Garcia from about
9:30 AM to 3 PM local time. Is this correct?

"T. Essel" (virtually stargazing, somewhere in cyberspace)

In article , wrote:
On 8 April 2005, it seems that a complete or nearly complete solar
eclipse should be visible from the Pitcairn Islands,
[SNIP]
An
interesting feature of this eclipse is that Venus should be visible only
two degrees away, which should further add to the drama of the event.
Are these predictions correct?


If you are wanting serious information about past/ present/ future
eclipses, then the SunEarth site at NASA is a very good start :
http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html
Following links there, I see that :
The path of this event begins as an annular eclipse but it changes to
total about 2200 km south of Tahiti. At maximum eclipse (UT), the
duration of totality is 45 seconds. Unfortunately, the total portion
of the track never crosses land. The path becomes annular again about
800 km west of Costa Rica. By the time the shadow reaches the coast
of Costa Rica, the annular phase will already be 12 seconds and
growing. After crossing Panama and Colombia, the central path ends
in Venezuela where a 33 second annular eclipse will occur at sunset.


On 3 November 2005, it seems that a complete or nearly complete solar
eclipse should be visible near Avila, Spain, with closest approach to
totality occuring at 10:58 AM local time.

Err, my friends 'Ammonite' and the 'MudSharks' were finalising
arrangements for this a few months ago. I thought they were talking about
OCTOBER 2005. Again, to NASA's pages:
On Monday, October 03, an annular eclipse of the Sun will be visible
from within a narrow corridor which traverses the Iberian Peninsula
and stretches across the African continent. A partial eclipse will
be seen within the much broader path of the Moon's penumbral shadow,
which includes Europe, western Asia, the Middle East, India and most
of Africa.
so my friend's plans appear to be in the correct month.

On 8 April 2005, as we probably all remember, there occured a transit of
Venus across the visible solar disk.

Huh? Have you got your calendar open at the right page?

I think you need to do some reading at the NASA site I cited
above. It's technically accurate. I used it to plan my eclipse photography
in '99 and I got a diamond ring where my father got rained on.

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

On Wed, 2 Mar 2005, Aidan Karley wrote:

The path of this event begins as an annular eclipse but it changes to
total about 2200 km south of Tahiti. At maximum eclipse (UT), the
duration of totality is 45 seconds. Unfortunately, the total portion of
the track never crosses land. The path becomes annular again about 800
km west of Costa Rica. By the time the shadow reaches the coast of
Costa Rica, the annular phase will already be 12 seconds and growing.
After crossing Panama and Colombia, the central path ends in Venezuela
where a 33 second annular eclipse will occur at sunset.

Cool!!!

On 3 November 2005, it seems that a complete or nearly complete solar
eclipse should be visible near Avila, Spain, with closest approach to
totality occuring at 10:58 AM local time.

Err, my friends 'Ammonite' and the 'MudSharks' were finalising
arrangements for this a few months ago. I thought they were talking
about OCTOBER 2005. Again, to NASA's pages:

Oops, month 10 is October, not November, iddnt? :-/

On Monday, October 03, an annular eclipse of the Sun will be visible
from within a narrow corridor which traverses the Iberian Peninsula

Cool, an annular eclipse!

and stretches across the African continent. A partial eclipse will
be seen within the much broader path of the Moon's penumbral shadow,
which includes Europe, western Asia, the Middle East, India and most
of Africa.

On 8 April 2005, as we probably all remember, there occured a transit of
Venus across the visible solar disk.

Er, 2004? ;-/

Thanks, Aidan! This is just what I wanted!

"T. Essel" (hiding somewhere in cyberspace)

in article lid, Aidan
Karley at lid wrote on 03/02/2005 02:04:

If you are wanting serious information about past/ present/ future
eclipses, then the SunEarth site at NASA is a very good start :
http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html
Following links there, I see that :
The path of this event begins as an annular eclipse but it changes to
total about 2200 km south of Tahiti. At maximum eclipse (UT), the
duration of totality is 45 seconds. Unfortunately, the total portion
of the track never crosses land. The path becomes annular again about
800 km west of Costa Rica. By the time the shadow reaches the coast
of Costa Rica, the annular phase will already be 12 seconds and
growing. After crossing Panama and Colombia, the central path ends
in Venezuela where a 33 second annular eclipse will occur at sunset.

how does an annular eclipse only last for 33 seconds. i s'pose there is
only one instant of time when the moon is perfectly smack-dab in front of
the sun (if it is at all), but if you allow any slop in the definition of
the elapsed time of the eclipse, isn't it longer than that?

when i lived in Hanover NH in 1993 and 94, in one of those years (i think it
was 94), i saw a total annular eclipse (i wish it was a total-TOTAL eclipse
of the sun) and it lasted for longer than that as i recall.

--

r b-j

"Imagination is more important than knowledge."

In article , robert
bristow-johnson writes:

how does an annular eclipse only last for 33 seconds. i s'pose there is
only one instant of time when the moon is perfectly smack-dab in front of
the sun (if it is at all), but if you allow any slop in the definition of
the elapsed time of the eclipse, isn't it longer than that?

when i lived in Hanover NH in 1993 and 94, in one of those years (i think it
was 94), i saw a total annular eclipse (i wish it was a total-TOTAL eclipse
of the sun) and it lasted for longer than that as i recall.

Consider how unlikely an eclipse is in the first place. It's not so
unlikely that the Moon passes in front of the Sun, since the entire
solar system is essentially in the same plane (it's about as flat as a
pizza box). However, it is rather unlikely that the Moon is the same
apparent size as the Sun. Earth's Moon is unusually large, compared to
the size of the planet it orbits. (There are larger moons, but the
planets they orbit are giants, so that in relation they are smaller.)
The same apparent size could come from a smaller Moon closer in, but it
would travel faster and the length of an eclipse would be much shorter.
A larger Moon further out would be better, but then the Moon would be
even larger with respect to the Earth.

This is even more astounding since the Moon is moving away from the
Earth (tidal friction slows down the Earth, and the Moon moves out to
compensate, conserving angular momentum). In the past, there was a long
time when there were no solar eclipses, and there will be a long time in
the future when there will also be no solar eclipses.

The Moon's orbit isn't exactly circular, so the exact distance varies a
bit from eclipse to eclipse, and thus the apparent size. If the Moon is
too far away, we get an annular eclipse. All things being equal, the
further away, the longer the (annular) eclipse will last. Also, the
more exact the alignment, the longer the eclipse. Also, the Earth is
spinning underneath, faster at the equator than at the poles, so the
length will depend on latitude and, since the transverse velocity is the
important one, also on the time of day.

Thus, the length of an eclipse varies from 0 to about 7 minutes.

robert bristow-johnson wrote:
how does an annular eclipse only last for 33 seconds. i s'pose there is
only one instant of time when the moon is perfectly smack-dab in front of
the sun (if it is at all), but if you allow any slop in the definition of
the elapsed time of the eclipse, isn't it longer than that?

when i lived in Hanover NH in 1993 and 94, in one of those years (i think it
was 94), i saw a total annular eclipse (i wish it was a total-TOTAL eclipse
of the sun) and it lasted for longer than that as i recall.


If the sun and moon have exactly the same angular size, the moon will
exactly cover the sun, and the eclipse duration will be zero seconds.
It gets longer on either side.

Cheers,

Phil Hobbs

In article , Robert
bristow-johnson wrote:
how does an annular eclipse only last for 33 seconds.

The last part of the eclipse (anything after 33 seconds) is
invisible due to the sun going below the horizon. There are quite
likely some assumptions about the levelness of the horizon there, the
air's refractive index (temperature?) ,and other stuff.

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57=B010'11" N, 02=B008'43" W (sub-tropical Aberdeen), 0.0212=
33

"robert bristow-johnson" wrote in message
...
in article lid, Aidan
Karley at lid wrote on 03/02/2005 02:04:

If you are wanting serious information about past/ present/ future
eclipses, then the SunEarth site at NASA is a very good start :
http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html
Following links there, I see that :
The path of this event begins as an annular eclipse but it changes to
total about 2200 km south of Tahiti. At maximum eclipse (UT), the
duration of totality is 45 seconds. Unfortunately, the total portion
of the track never crosses land. The path becomes annular again about
800 km west of Costa Rica. By the time the shadow reaches the coast
of Costa Rica, the annular phase will already be 12 seconds and
growing. After crossing Panama and Colombia, the central path ends
in Venezuela where a 33 second annular eclipse will occur at sunset.

how does an annular eclipse only last for 33 seconds. i s'pose there is
only one instant of time when the moon is perfectly smack-dab in front of
the sun (if it is at all), but if you allow any slop in the definition of
the elapsed time of the eclipse, isn't it longer than that?

No, an annular is when the sun appears as a ring surrounding the Moon, and it
may last a couple of minutes to as short as a second or so. The length depends
on the apparent size of the Moon; the smaller the size, the longer the annular.


when i lived in Hanover NH in 1993 and 94, in one of those years (i think it
was 94), i saw a total annular eclipse (i wish it was a total-TOTAL eclipse
of the sun) and it lasted for longer than that as i recall.

I believe "total" only refers to those cases where apparent size of the Moon is
large enough to cover the entire disk of the Sun. These are the ones where you
see the Corona of the Sun around the dark disk of the Moon. With an annular,
even that little bit of the Sun peeking around the edge of the Moon is
sufficient to prevent you from seeing the Corona.
--
Sincerely,
--- Dave
----------------------------------------------------------------------
It don't mean a thing
unless it has that certain "je ne sais quoi"
Duke Ellington
----------------------------------------------------------------------

In message lid, Aidan
Karley writes
In article , wrote:

On 3 November 2005, it seems that a complete or nearly complete solar
eclipse should be visible near Avila, Spain, with closest approach to
totality occuring at 10:58 AM local time.

Err, my friends 'Ammonite' and the 'MudSharks' were finalising
arrangements for this a few months ago. I thought they were talking about
OCTOBER 2005. Again, to NASA's pages:
.

This thread should probably be on an unmoderated group, but here goes!
"Finalising"? I haven't started planning yet, apart from marking the
date :-)
Where do they plan to go?
--
Mail to jsilverlight AT merseia DOT fsnet DOT co DOT uk is welcome.


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