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What is the Darkest Hour of the Night?



 
 
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  #11  
Old October 10th 04, 08:41 PM
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John Ladasky writes:

George Dishman wrote:


It will be darkest at local midnight in midwinter
when the Moon is new and Venus is below the horizon.
I wonder how often that combination occurs (if ever).


How can Venus *not* be below the horizon at local midnight? Venus
reaches a maximum elongation of about 48 degrees relative to the Sun.
If I've done the math correctly, Venus should always be below the
horizon by 3 hours and 12 minutes after sunset.


For locations near the equator, yes. Near the poles, however,
it is possible for the Sun to be down and Venus to be up at
local midnight.

  #12  
Old October 11th 04, 09:39 PM
George Dishman
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"John Ladasky" wrote in message
om...
"George Dishman" wrote in message

...
"Eugene Shubert" wrote in
message om...
"Mr. 4X" wrote in message

...
(Eugene Shubert) wrote in

message
om:

What is the darkest hour of the night?

That depends on a lot of things. There is almost no direct sunlight

2-3
hours after sunset,

Isn't there a measurable amount of sunlight that's scattered by the
atmosphere, reaching further into the night than a mere 2-3 hours of
earth rotation?


Zodiacal light.


I thought that the zodiacal light was scattered off of Solar System
dust in the plane of the ecliptic, rather than Earth's atmosphere?


Yes, I was unclear. When Eugene said "Isn't there a
measurable amount of sunlight that's scattered ..."
I wondered if he was recalling discussion of the
Zodiacal light rather than atmospheris scatter.
I was too economical with my words (most unusual).

It will be darkest at local midnight in midwinter
when the Moon is new and Venus is below the horizon.
I wonder how often that combination occurs (if ever).


How can Venus *not* be below the horizon at local midnight? Venus
reaches a maximum elongation of about 48 degrees relative to the Sun.
If I've done the math correctly, Venus should always be below the
horizon by 3 hours and 12 minutes after sunset.


Again I stand corrected. It should have been obvious
to me since Venus is inside our orbit. Thanks for
picking me up on those.

best regards
George


  #13  
Old October 12th 04, 04:43 AM
John Ladasky
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"George Dishman" wrote in message ...
"John Ladasky" wrote in message
om...
"George Dishman" wrote in message

...
"Eugene Shubert" wrote in
message om...
"Mr. 4X" wrote in message

...


Isn't there a measurable amount of sunlight that's scattered by the
atmosphere, reaching further into the night than a mere 2-3 hours of
earth rotation?

Zodiacal light.


I thought that the zodiacal light was scattered off of Solar System
dust in the plane of the ecliptic, rather than Earth's atmosphere?


Yes, I was unclear. When Eugene said "Isn't there a
measurable amount of sunlight that's scattered ..."
I wondered if he was recalling discussion of the
Zodiacal light rather than atmospheris scatter.
I was too economical with my words (most unusual).

It will be darkest at local midnight in midwinter
when the Moon is new and Venus is below the horizon.
I wonder how often that combination occurs (if ever).


How can Venus *not* be below the horizon at local midnight? Venus
reaches a maximum elongation of about 48 degrees relative to the Sun.
If I've done the math correctly, Venus should always be below the
horizon by 3 hours and 12 minutes after sunset.


Again I stand corrected. It should have been obvious
to me since Venus is inside our orbit. Thanks for
picking me up on those.


Actually, Dave Tholen corrected *me* on this one. Thanks, Dave -- and
apologies to you, George.

If you're near one of the poles, it is possible for a night to be
under 6 hours and 24 minutes long. On such nights, the Sun makes a
really shallow excursion below the horizon. Venus will follow the
same path, more or less. In this case, it is possible for Venus to
be above the horizon at midnight.

Eyeballing a few web pages, I conclude that nights can be this short
above about 57°N, or below 57°S. Hey, seeing Venus at midnight isn't
that infrequent an occurrence, then. Nearly all of Alaska, half of
Canada, Greenland, Iceland, Scandinavia, and half of Russia are above
this line. Unless you count scientific stations on Antarctica, there
aren't any inhabited places below 57°S.

--
Rainforest laid low.
"Wake up and smell the ozone,"
Says man with chainsaw.
John J. Ladasky Jr., Ph.D.
  #14  
Old October 12th 04, 06:03 AM
Mike Schwab
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I recall a complaint from an astronomer in Scotland wanting fall to come
around so he could do some observing, the sun is too close to the
horizon for the stars to come out in the summer.

John Ladasky wrote:
=


"George Dishman" wrote in message news:1097=

...
"John Ladasky" wrote in message
om...
"George Dishman" wrote in message

...
"Eugene Shubert" wrot=

e in
message om...
"Mr. 4X" wrote in message

...

=


Isn't there a measurable amount of sunlight that's scattered by=

the
atmosphere, reaching further into the night than a mere 2-3 hou=

rs of
earth rotation?

Zodiacal light.

I thought that the zodiacal light was scattered off of Solar System=


dust in the plane of the ecliptic, rather than Earth's atmosphere?


Yes, I was unclear. When Eugene said "Isn't there a
measurable amount of sunlight that's scattered ..."
I wondered if he was recalling discussion of the
Zodiacal light rather than atmospheris scatter.
I was too economical with my words (most unusual).

It will be darkest at local midnight in midwinter
when the Moon is new and Venus is below the horizon.
I wonder how often that combination occurs (if ever).

How can Venus *not* be below the horizon at local midnight? Venus
reaches a maximum elongation of about 48 degrees relative to the Su=

n.
If I've done the math correctly, Venus should always be below the
horizon by 3 hours and 12 minutes after sunset.


Again I stand corrected. It should have been obvious
to me since Venus is inside our orbit. Thanks for
picking me up on those.

=


Actually, Dave Tholen corrected *me* on this one. Thanks, Dave -- and
apologies to you, George.
=


If you're near one of the poles, it is possible for a night to be
under 6 hours and 24 minutes long. On such nights, the Sun makes a
really shallow excursion below the horizon. Venus will follow the
same path, more or less. In this case, it is possible for Venus to
be above the horizon at midnight.
=


Eyeballing a few web pages, I conclude that nights can be this short
above about 57=B0N, or below 57=B0S. Hey, seeing Venus at midnight isn=

't
that infrequent an occurrence, then. Nearly all of Alaska, half of
Canada, Greenland, Iceland, Scandinavia, and half of Russia are above
this line. Unless you count scientific stations on Antarctica, there
aren't any inhabited places below 57=B0S.
=


--
Rainforest laid low.
"Wake up and smell the ozone,"
Says man with chainsaw.
John J. Ladasky Jr., Ph.D.

 




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