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What is the Darkest Hour of the Night?



 
 
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  #1  
Old October 9th 04, 04:28 PM
Eugene Shubert
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Default What is the Darkest Hour of the Night?

What is the darkest hour of the night?

Eugene Shubert
http://www.everythingimportant.org
  #2  
Old October 9th 04, 06:50 PM
Prai Jei
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Eugene Shubert (or somebody else of the same name) wrote thusly in message
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What is the darkest hour of the night?

Eugene Shubert
http://www.everythingimportant.org


Isn't it supposed to be just before dawn?

Sounds unlikely on scientific grounds though, so I'd say it's around the
(real local) midnight.
--
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  #3  
Old October 10th 04, 12:46 AM
Eugene Shubert
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Prai Jei wrote in message ...
Eugene Shubert (or somebody else of the same name) wrote thusly in message
:

What is the darkest hour of the night?

Eugene Shubert
http://www.everythingimportant.org


Isn't it supposed to be just before dawn?


Yes.

Sounds unlikely on scientific grounds though, so I'd say it's
around the (real local) midnight.


Googling the phrase "It's always darkest before dawn" turn up 1750
hits. An astronomer should know when it really is the darkest hour
of the night. I'm looking for a confident, scientifically measured
answer, not a reasonable guess.

Eugene Shubert
http://www.everythingimportant.org
  #8  
Old October 10th 04, 07:49 PM
John Ladasky
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"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?

When a sizable part of the earth's surface and atmosphere is heated up
during the day, doesn't a measurable fraction of that heated material
reradiate energy in the visible spectrum?

To keep the calculations simple, let's ignore artificial lighting but
factor in the reflected light of the Moon if you know how to do that.


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.

George


--
Rainforest laid low.
"Wake up and smell the ozone,"
Says man with chainsaw.
John J. Ladasky Jr., Ph.D.
  #9  
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.

  #10  
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


 




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