10 ms·

Is it possible for a lunar eclipse to occur before sunset?

137 points by georgecmu 4y ago

jefftk 4y ago
Wikipedia has a picture from 2014: https://en.wikipedia.org/wiki/File:Lunar_eclipse_at_sunrise_Minneapolis_October_2014.png https://en.wikipedia.org/wiki/File:Lunar_eclipse_at_sunrise_... Here's a nice post thinking through how you might actually observe this: https://photoephemeris.com/articles/the-selenelion-challenge https://photoephemeris.com/articles/the-selenelion-challenge
codetrotter 4y ago
[flagged]
- mendelab 4y ago
  Technically correct, but misses the point :)
  - codetrotter 4y ago
    [flagged]
    - codetrotter 4y ago
      [flagged]
IncRnd 4y ago
Yes, a selenelion will happen just before sunset or just after sunrise when the sun and moon are at opposite points of the horizon. This is also called a horizontal eclipse and is due to the atmosphere not the planet. [1] [2] [1] https://sciencenotes.org/selenelion-eclipse/ https://sciencenotes.org/selenelion-eclipse/ [2] https://www.space.com/27338-total-lunar-eclipse-rare-sunrise-selenelion.html https://www.space.com/27338-total-lunar-eclipse-rare-sunrise...
JEDI-HACKER 4y ago
Yes always possible. If you consider the light spectrum is split during sun set and rise. So you will get more red light spectrum, during set/rise. You will see more green during night ie Nothern lights. And obviously mostly blue during the day.
- jjtheblunt 4y ago
  i just realized you explained the red dawn and red dusk in Arizona, far more scientifically than the urban legend that it's "pollution from California".
  - kadoban 4y ago
    It is mostly caused by particulate matter in the air. Not so much pollution from California, though I'm sure a bit of it is. More likely to be dust and our own pollution.
    - jjtheblunt 4y ago
      is there a citation for that? the reason i ask is the parent comment talks about the scattering of light at sharp incidence levels favoring certain wavelengths, with the reds being what naturally is dominant at dusk and dawn light-hitting-atmosphere angles. https://www.metoffice.gov.uk/weather/learn-about/weather/optical-effects/why-is-the-sunset-red https://www.metoffice.gov.uk/weather/learn-about/weather/opt...
      - kadoban 4y ago
        Looked through a few pages, this one I think explains it fairly well https://demos.smu.ca/index.php/demos/astronomy/35-red-sunsets https://demos.smu.ca/index.php/demos/astronomy/35-red-sunset... The answer it gives is more of a combination of what I thought and what the parent said, tl;dr version: scattering both due to just normal oxygen and nitrogen composition of the air and also pollutants (which I think dust would also qualify, though most things I could find that specified were talking more about sulfur compounds).
supernova87a 4y ago
It is possible (atmospheric effects as stated by others/the article), but not in a useful sense of having something that looks impressively like a lunar eclipse. In other trivia, expect that a solar eclipse will also happen somewhere on Earth in any month that has a lunar eclipse. (exactly because of similar alignment issues)
- deleted 4y ago
  [deleted]
- gweinberg 4y ago
  Isn't that only true the other way around? The earth is bigger than the moon, so I'd think sometimes you'd get a total lunar eclipse when there's only a partial corresponding solar eclipse, and diddly when there's only a partial lunar eclipse.
  - supernova87a 4y ago
    Oh, I don't mean exactly the same magnitude of eclipse -- just that whether annular/partial/etc, if there is a lunar eclipse, there will generally be a solar eclipse (of any type).
deleted 4y ago
[deleted]
Taniwha 4y ago
A lunar eclipse can happen at any time of the day, might only be visible on the other side of the planet - maybe the question he meant to ask was "can you see ...."
- jojobas 4y ago
  Every lunar eclipse happens at every possible time of the day, simultaneously.
  - addaon 4y ago
    And all lunar eclipses, except possibly the last one, precede at least one sunset.
    - dredmorbius 4y ago
      Hrm... The Moon's orbit will decay to the point that solar eclipses are no longer possible in about 600 million years. The Sun will continue to rise and set following that point, in all likelihood. This is however about the same time that the carbon-silicate cycle will have been disrupted to the point that C3 photosynthesis is no longer possible. Humans (or their descendant species) may not be observing either lunar or solar eclipses by that time, at least not from Earth. And by 1.5--4.5 billion years from now, still within the main solar sequence, the Moon will have drifted far enough from the Earth that the Earth's axis is no longer stabilised by the Moon. By this point, even lunar eclipses might no longer be possible. (The other factor is that the Moon drifts so far out that it orbits outside the Earth's umbra, such that total lunar eclipses no longer occur, though "blood moon" penumbral eclipses could still happen. I don't know what the timeline for this might be. But again, so long as the Earth itself rotates and isn't consumed by the Sun, sunsets will still occur.) By 800 my to 1.6 by, solar luminosity will have increased to the point that life on Earth's surface is likely impossible. Wikipedia, "Timeline of the Far Future": <https://en.wikipedia.org/wiki/Timeline_of_the_far_future https://en.wikipedia.org/wiki/Timeline_of_the_far_future> Sidenote: Past events are designated using the abbreviations kya, mya, bya, etc., (thousand, million, billion years ago). I'm not aware of a standard abbreviation for time in the future, though it would seem kyf, myf, byf, etc., might be reasonably used for this. Or perhaps "kyp" or "kyn" (thousand years from present, thousand years from now). Seems that "FY" has at least some support: <https://www.abbreviations.com/abbreviation/future%20years https://www.abbreviations.com/abbreviation/future%20years>
yuliyp 4y ago
Sunset is kind of a fluid thing. The lunar eclipse on May 15 last year happened right around sunset as viewed in the SF bay area. A little way further south or west would have been an even brighter sky for the eclipse. https://photos.app.goo.gl/pjbefmFcv2THZEQ19 https://photos.app.goo.gl/pjbefmFcv2THZEQ19 are a few photos I took of this. The red of the eclipse was initially almost invisible due to how much light there still was in the sky, and it only became clearer as the ambient light diminished.
antognini 4y ago
Back in Classical Greece there was some debate as to what the cause of a lunar eclipse was. By this time it was generally accepted that it was due to the Earth coming between the Moon and the Sun and casting a shadow. But one point of evidence that was presented against this theory was that on occasion lunar eclipses were observed at sunset. You could clearly see both the Sun and the Moon, so the Earth did not appear to be between the two. This issue with the idea that lunar eclipses are due to the Earth's shadow wasn't really satisfactorily addressed until the 1700s or so when the refraction of light was systematically studied (though by the Hellenistic Era no one seriously doubted it). This actually wasn't the only time when the refraction of the Earth's atmosphere produced surprising observations in the ancient world. One of the devices the Greeks used to determine the time of an equinox was what is called an equatorial ring. It's basically just a metal hoop oriented at an angle equal to 90 degrees minus the latitude. (Here's a diagram: https://en.wikipedia.org/wiki/Equatorial_ring#/media/File:Equatorial_ring.png https://en.wikipedia.org/wiki/Equatorial_ring#/media/File:Eq...) During an equinox the Sun would be right on the celestial equator, and the shadow cast by the upper half of the hoop would fall exactly on the bottom half. But it was noticed that sometimes, the shadow would fall on the bottom half early in the morning, then cross to the other side, cross back, and then later cross over once again --- it seemed that there was three equinoxes! Ptolemy explained this away as being due to instabilities in the device's orientation --- somehow it was very slightly tilting and so it wasn't possible to measure the time of the equinox to better than half a day or so. But today we know that this was also due to the refraction of the atmosphere. Early in the morning, the Sun would be refracted to appear to be just above the celestial equator, but as it rose, the refraction would lessen and it would fall back to its original place. Then later in the day it would cross the celestial equator "for real" when the equinox actually occurred. So the device was much more accurate than ancient astronomers gave it credit for!
- TheSpiceIsLife 4y ago
  That's the canonical version of the story. I wonder if anyone back then, say an armchair astronomer, tried to argue that it was due to the atmosphere, and backed their argument up by comparing the atmosphere to how a pool of water bends light. We'll never know.
amelius 4y ago
Betteridge says no, but the headline says yes. https://en.wikipedia.org/wiki/Betteridge%27s_law_of_headlines https://en.wikipedia.org/wiki/Betteridge%27s_law_of_headline... Perhaps there should be an exception for Stackoverflow.
- omnicognate 4y ago
  This is the difference between a title and a headline.

137 points by georgecmu 4y ago

Wikipedia has a picture from 2014: https://en.wikipedia.org/wiki/File:Lunar_eclipse_at_sunrise_Minneapolis_October_2014.png https://en.wikipedia.org/wiki/File:Lunar_eclipse_at_sunrise_... Here's a nice post thinking through how you might actually observe this: https://photoephemeris.com/articles/the-selenelion-challenge https://photoephemeris.com/articles/the-selenelion-challenge

codetrotter 4y ago

[flagged]

mendelab 4y ago
Technically correct, but misses the point :)
- codetrotter 4y ago
  [flagged]
  - codetrotter 4y ago
    [flagged]

IncRnd 4y ago

Yes, a selenelion will happen just before sunset or just after sunrise when the sun and moon are at opposite points of the horizon. This is also called a horizontal eclipse and is due to the atmosphere not the planet. [1] [2] [1] https://sciencenotes.org/selenelion-eclipse/ https://sciencenotes.org/selenelion-eclipse/ [2] https://www.space.com/27338-total-lunar-eclipse-rare-sunrise-selenelion.html https://www.space.com/27338-total-lunar-eclipse-rare-sunrise...

JEDI-HACKER 4y ago

Yes always possible. If you consider the light spectrum is split during sun set and rise. So you will get more red light spectrum, during set/rise. You will see more green during night ie Nothern lights. And obviously mostly blue during the day.

jjtheblunt 4y ago
i just realized you explained the red dawn and red dusk in Arizona, far more scientifically than the urban legend that it's "pollution from California".
- kadoban 4y ago
  It is mostly caused by particulate matter in the air. Not so much pollution from California, though I'm sure a bit of it is. More likely to be dust and our own pollution.
  - jjtheblunt 4y ago
    is there a citation for that? the reason i ask is the parent comment talks about the scattering of light at sharp incidence levels favoring certain wavelengths, with the reds being what naturally is dominant at dusk and dawn light-hitting-atmosphere angles. https://www.metoffice.gov.uk/weather/learn-about/weather/optical-effects/why-is-the-sunset-red https://www.metoffice.gov.uk/weather/learn-about/weather/opt...
    - kadoban 4y ago
      Looked through a few pages, this one I think explains it fairly well https://demos.smu.ca/index.php/demos/astronomy/35-red-sunsets https://demos.smu.ca/index.php/demos/astronomy/35-red-sunset... The answer it gives is more of a combination of what I thought and what the parent said, tl;dr version: scattering both due to just normal oxygen and nitrogen composition of the air and also pollutants (which I think dust would also qualify, though most things I could find that specified were talking more about sulfur compounds).

supernova87a 4y ago

It is possible (atmospheric effects as stated by others/the article), but not in a useful sense of having something that looks impressively like a lunar eclipse. In other trivia, expect that a solar eclipse will also happen somewhere on Earth in any month that has a lunar eclipse. (exactly because of similar alignment issues)

deleted 4y ago
[deleted]
gweinberg 4y ago
Isn't that only true the other way around? The earth is bigger than the moon, so I'd think sometimes you'd get a total lunar eclipse when there's only a partial corresponding solar eclipse, and diddly when there's only a partial lunar eclipse.
- supernova87a 4y ago
  Oh, I don't mean exactly the same magnitude of eclipse -- just that whether annular/partial/etc, if there is a lunar eclipse, there will generally be a solar eclipse (of any type).

deleted 4y ago

[deleted]

Taniwha 4y ago

A lunar eclipse can happen at any time of the day, might only be visible on the other side of the planet - maybe the question he meant to ask was "can you see ...."

jojobas 4y ago
Every lunar eclipse happens at every possible time of the day, simultaneously.
- addaon 4y ago
  And all lunar eclipses, except possibly the last one, precede at least one sunset.
  - dredmorbius 4y ago
    Hrm... The Moon's orbit will decay to the point that solar eclipses are no longer possible in about 600 million years. The Sun will continue to rise and set following that point, in all likelihood. This is however about the same time that the carbon-silicate cycle will have been disrupted to the point that C3 photosynthesis is no longer possible. Humans (or their descendant species) may not be observing either lunar or solar eclipses by that time, at least not from Earth. And by 1.5--4.5 billion years from now, still within the main solar sequence, the Moon will have drifted far enough from the Earth that the Earth's axis is no longer stabilised by the Moon. By this point, even lunar eclipses might no longer be possible. (The other factor is that the Moon drifts so far out that it orbits outside the Earth's umbra, such that total lunar eclipses no longer occur, though "blood moon" penumbral eclipses could still happen. I don't know what the timeline for this might be. But again, so long as the Earth itself rotates and isn't consumed by the Sun, sunsets will still occur.) By 800 my to 1.6 by, solar luminosity will have increased to the point that life on Earth's surface is likely impossible. Wikipedia, "Timeline of the Far Future": <https://en.wikipedia.org/wiki/Timeline_of_the_far_future https://en.wikipedia.org/wiki/Timeline_of_the_far_future> Sidenote: Past events are designated using the abbreviations kya, mya, bya, etc., (thousand, million, billion years ago). I'm not aware of a standard abbreviation for time in the future, though it would seem kyf, myf, byf, etc., might be reasonably used for this. Or perhaps "kyp" or "kyn" (thousand years from present, thousand years from now). Seems that "FY" has at least some support: <https://www.abbreviations.com/abbreviation/future%20years https://www.abbreviations.com/abbreviation/future%20years>

yuliyp 4y ago

Sunset is kind of a fluid thing. The lunar eclipse on May 15 last year happened right around sunset as viewed in the SF bay area. A little way further south or west would have been an even brighter sky for the eclipse. https://photos.app.goo.gl/pjbefmFcv2THZEQ19 https://photos.app.goo.gl/pjbefmFcv2THZEQ19 are a few photos I took of this. The red of the eclipse was initially almost invisible due to how much light there still was in the sky, and it only became clearer as the ambient light diminished.

antognini 4y ago

Back in Classical Greece there was some debate as to what the cause of a lunar eclipse was. By this time it was generally accepted that it was due to the Earth coming between the Moon and the Sun and casting a shadow. But one point of evidence that was presented against this theory was that on occasion lunar eclipses were observed at sunset. You could clearly see both the Sun and the Moon, so the Earth did not appear to be between the two. This issue with the idea that lunar eclipses are due to the Earth's shadow wasn't really satisfactorily addressed until the 1700s or so when the refraction of light was systematically studied (though by the Hellenistic Era no one seriously doubted it). This actually wasn't the only time when the refraction of the Earth's atmosphere produced surprising observations in the ancient world. One of the devices the Greeks used to determine the time of an equinox was what is called an equatorial ring. It's basically just a metal hoop oriented at an angle equal to 90 degrees minus the latitude. (Here's a diagram: https://en.wikipedia.org/wiki/Equatorial_ring#/media/File:Equatorial_ring.png https://en.wikipedia.org/wiki/Equatorial_ring#/media/File:Eq...) During an equinox the Sun would be right on the celestial equator, and the shadow cast by the upper half of the hoop would fall exactly on the bottom half. But it was noticed that sometimes, the shadow would fall on the bottom half early in the morning, then cross to the other side, cross back, and then later cross over once again --- it seemed that there was three equinoxes! Ptolemy explained this away as being due to instabilities in the device's orientation --- somehow it was very slightly tilting and so it wasn't possible to measure the time of the equinox to better than half a day or so. But today we know that this was also due to the refraction of the atmosphere. Early in the morning, the Sun would be refracted to appear to be just above the celestial equator, but as it rose, the refraction would lessen and it would fall back to its original place. Then later in the day it would cross the celestial equator "for real" when the equinox actually occurred. So the device was much more accurate than ancient astronomers gave it credit for!

TheSpiceIsLife 4y ago
That's the canonical version of the story. I wonder if anyone back then, say an armchair astronomer, tried to argue that it was due to the atmosphere, and backed their argument up by comparing the atmosphere to how a pool of water bends light. We'll never know.

amelius 4y ago

Betteridge says no, but the headline says yes. https://en.wikipedia.org/wiki/Betteridge%27s_law_of_headlines https://en.wikipedia.org/wiki/Betteridge%27s_law_of_headline... Perhaps there should be an exception for Stackoverflow.

omnicognate 4y ago
This is the difference between a title and a headline.