Watching Eclipses From Space

[sevenperforce]

Got to watch Sunday's Super Blood Wolf Moon (phew) which was cool, as always.

Made me think...what would it be like to watch a solar or lunar eclipse from the moon? How about seeing a lunar eclipse from high lunar orbit? What about a Phobosian eclipse from Mars? 

Wrote this article for Medium about how it would look to stand on the surface of the moon during an eclipse.

Spoiler

 

Edited January 23, 2019 by sevenperforce

[Xd the great]

Solar eclipse: nothing so special.

Lunar eclipse: earth blocking the Sun.

[Green Baron]

I find satellite images of the moon's shadow on the earth impressive.

[lajoswinkler]

That NASA's artistic drawing is so incorrect it hurts to look at it. It's absurd.

One would not see the stars and most certainly not the human made lights on Earth. Both are way too dim and our eyes would be saturated by the light of the fiery looking atmosphere to notice anything else.

 

 

[Green Baron]

Glad i am not a vampire :-)

From my place, the difference in exposure time for the moon from earth between the penumbral and the fully lit phase was 16 seconds to 1/60s (f/8, ISO100), that is 10ev difference (logarithmic scale, each ev is double the light of the former). The sky was clear due to a foehn effect.

I assume the video is not colour corrected or processed in some way, @lajoswinkler ? It would be interesting to know if the sun rose above the ocean or a continent (dust, moisture), and how much of the bright white is eventually due to saturation of the sensor ...

Btw.: they can do better:

https://www.nasa.gov/content/sunrise-from-the-international-space-station

https://www.nasa.gov/multimedia/imagegallery/image_feature_385.html

 

Edited January 24, 2019 by Green Baron

[YNM]

18 hours ago, sevenperforce said:

what would it be like to watch a solar or lunar eclipse from the moon?

Solar eclipse : you'd be in nighttime. Or daytime.

Lunar eclipse : the whole Moon be in nightime.

Elsewhere : "Oh look, two blobs" ! or "Oh look, one blob !"

Edited January 24, 2019 by YNM

[sevenperforce]

2 hours ago, lajoswinkler said:

That NASA's artistic drawing is so incorrect it hurts to look at it. It's absurd.

One would not see the stars and most certainly not the human made lights on Earth. Both are way too dim and our eyes would be saturated by the light of the fiery looking atmosphere to notice anything else.

Is that realtime? I wonder if the motion of the satellite taking the imagery had anything to do with the appearance.

At the height of totality, the atmospheric distortion could well be low enough that it would be much dimmer.

40 minutes ago, YNM said:

Solar eclipse : you'd be in nighttime. Or daytime.

During a solar eclipse you could see the moon's shadow cast on earth much more clearly than from, say, the Space Station. There wouldn't be a terrific light show or anything, but the sense of movement would be much more visible...watching your own shadow track across the Earth would let you sense your own movement through space.

40 minutes ago, YNM said:

Lunar eclipse : the whole Moon be in nightime.

A glowing red ring in the sky might still be in the cards if you were looking while the moon was at the very center of the Earth's umbra.

The NASA animation clearly showed too broad a dynamic range. No way any part of the Earth would be visible against that much of the sun's disc.

But I played around with contrast and saturation to try and get a closer approximation of what it WOULD look like and I think it's closer:

So a notably red ring is possible, I think.

[Green Baron]

12 minutes ago, sevenperforce said:

So a notably red ring is possible, I think.

Possible, why not. Colour and brightness depend on atmospheric composition and contents and can vary between a yellow/golden and reddish/brown. It has been proposed to try and use lunar eclipses as an indicator for the atmosphere's contents.

Are there no images of a solar eclipse from geostationary orbit or other satellite than the ISS and weather satellites ? These show the lower atmosphere yellowish and the upper blue, just like a clear air sunset.

Edited January 24, 2019 by Green Baron

[YNM]

1 minute ago, sevenperforce said:

During a solar eclipse you could see the moon's shadow cast on earth much more clearly than from, say, the Space Station.

Only if you're on the lunar nighttime.

1 minute ago, sevenperforce said:

A glowing red ring in the sky might still be in the cards if you were looking while the moon was at the very center of the Earth's umbra.

Definitely it'll be very very thin, and most of it will be bluish. It's the same as our standard sky.

Gah, I forgot the name of the phenomenon where the apparent color of the mineral is different from the 'shadow' color of the mineral...

[sevenperforce]

35 minutes ago, Green Baron said:

Possible, why not. Colour and brightness depend on atmospheric composition and contents and can vary between a yellow/golden and reddish/brown. It has been proposed to try and use lunar eclipses as an indicator for the atmosphere's contents.

Primary cause of color in lunar eclipses is differential Rayleigh scattering. 

35 minutes ago, Green Baron said:

Are there no images of a solar eclipse from geostationary orbit or other satellite than the ISS and weather satellites ? These show the lower atmosphere yellowish and the upper blue, just like a clear air sunset.

ISS and weather satellites don't get far enough from Earth to pick up atmospheric scattering at any point other than local sunrise and local sunset. 

28 minutes ago, YNM said:

Definitely it'll be very very thin, and most of it will be bluish. It's the same as our standard sky.

Gah, I forgot the name of the phenomenon where the apparent color of the mineral is different from the 'shadow' color of the mineral...

100% incorrect. It's not at all the color of the standard sky; it's red. That's why the lunar surface turns red.

Rayleigh scattering scatters higher-energy photons at a higher angle than lower-energy photons. Example:

White light, a broad spectrum of photons, enters the gem from the right. Blue photons are scattered in every direction, causing the entire gem to appear broadly blue in color, while red-orange light is not significantly scattered and instead passes through (with some refraction) to cast an orange glow.

It's the same with the sky. The sky scatters blue photons, which makes the sky look blue, but the sun looks orange when you look at the light it casts on the ground.

When it comes to a lunar eclipse, the Earth occludes ALL sunlight except for what is scattered, and almost all light is scattered at such a high angle that it cannot reach the moon. The only light that is scattered at a low enough angle to reach the moon is red, which is why the moon turns red in a lunar eclipse.

[YNM]

20 minutes ago, sevenperforce said:

The sky scatters blue photons, which makes the sky look blue, but the sun looks orange when you look at the light it casts on the ground.

Yeah, this probably be the case, but I'm sure the ring isn't that red - the "red" portion be very thin down on the earth limb, but the extended sky will still look blue. And 100 km thin air on top of 12700 km diameter ball is probably really thin, barely 1%, and so won't be that visible.

What a 24 km haze + 200 km (176 remaining) tenuous atmo looks like on a 2400 km diameter ball :

Edited January 24, 2019 by YNM

[Green Baron]

Other way round, satellites, because they are closer, must travel through the zone of scattering and show the effect of changes of wavelengths much clearer than the moon. But i was asking for images from GEO as a satellite there spends a longer time traveling through the shadow phases.

Anyway, the moon isn't always that read, this time Anak Krakatau migth have played a role in the hue (not my speculation) and the alignment of the earth's continents (African deserts, densely populated Asia, my speculation).

Such a ring as in the picture is a nice rendering to visualize the principle, but not necessarily reality.

Waiting for the first real picture from the moon :-)

Edited January 24, 2019 by Green Baron

[sevenperforce]

13 minutes ago, YNM said:

Yeah, this probably be the case, but I'm sure the ring isn't that red - the "red" portion be very thin down on the earth limb, but the extended sky will still look blue. And 100 km thin air on top of 12700 km diameter ball is probably really thin, barely 1%, and so won't be that visible.

What a 24 km haze + 200 km (176 remaining) tenuous atmo looks like on a 2400 km diameter ball :

Spoiler

 

I do not believe any blue will be visible at all.

Here's a diagram. Scales are way off, obviously, but the scattering angle is also amplified so it works the same way:

At (A), the moon is fully illuminated.

At (B), we see part of the earth's shadow cast on the moon, but it is so bright that it washes out our ability to see red light cast on the moon. A lunar observer standing exactly on the terminator would see the sun blindingly bright at the edge of the Earth's disc.

At (C), the moon is fully within the scattering-only region. The ring of atmosphere appears red because the light which is scattered at a low angle is roughly 20 times brighter than the blue diffuse sky radiation (skyshine has an intensity of 5% that of sunlight). 

20 minutes ago, Green Baron said:

Other way round, satellites, because they are closer, must travel through the zone of scattering and show the effect of changes of wavelengths much clearer than the moon. But i was asking for images from GEO as a satellite there spends a longer time traveling through the shadow phases.

Satellites, even geostationary ones, pass through the black triangle of total shadow and thus never would be able to observe the entire atmosphere at once, though there is a chance that geostationary satellites would be able to see a small ring-section of Earth's atmosphere glowing red for a longer time shortly after local sunset or just before local sunrise.

At sunrise or sunset, we are able to get scattering from the light directly above us before the sun's direct rays reach us, which mixes things up. From the moon, you wouldn't see any of that; you'd only see the red light.

 

[Green Baron]

I am not sure if satellites in GEO could not capture the effect, but i am neither sure they would. Anyway, a lot can be done from the surface of the earth. Lets add real world data from observation to the ideal model and we find that the moon's colour and brightness do not always obey and the contents of the atmosphere decisively influence scattering and other optical effects.

Up to a degree that it has been proposed to use the moon's reflected light as an indicator.

[YNM]

15 hours ago, sevenperforce said:

The ring of atmosphere appears red because the light which is scattered at a low angle is roughly 20 times brighter than the blue diffuse sky radiation (skyshine has an intensity of 5% that of sunlight). 

I've tried to drawn one to scale in CAD, and indeed the moon falls within the refraction area (assuming 1 degree refraction).

Still, the red layer is going to be very very thin, and unless you're equipped with an optical instrument it won't be noticeable.

[lajoswinkler]

23 hours ago, Green Baron said:

Glad i am not a vampire :-)

From my place, the difference in exposure time for the moon from earth between the penumbral and the fully lit phase was 16 seconds to 1/60s (f/8, ISO100), that is 10ev difference (logarithmic scale, each ev is double the light of the former). The sky was clear due to a foehn effect.

I assume the video is not colour corrected or processed in some way, @lajoswinkler ? It would be interesting to know if the sun rose above the ocean or a continent (dust, moisture), and how much of the bright white is eventually due to saturation of the sensor ...

Btw.: they can do better:

https://www.nasa.gov/content/sunrise-from-the-international-space-station

https://www.nasa.gov/multimedia/imagegallery/image_feature_385.html

 

Kaguya had two color TV cameras for taking HDTV color video. One telephoto at 15° and one at 44°.

As far as I know, it was not color processed.

http://www.kaguya.jaxa.jp/en/equipment/hdtv_e.htm

 

20 hours ago, sevenperforce said:

Is that realtime? I wonder if the motion of the satellite taking the imagery had anything to do with the appearance.

A glowing red ring in the sky might still be in the cards if you were looking while the moon was at the very center of the Earth's umbra.

Yes, it's realtime, it's taken through a 15° telephoto HDTV color camera.

And yes, we'd notice red only if we're standing near or at the center of umbra.

Reason #1 - color we perceive depends on the amount of photons, too. Intense light will be white, no matter what wavelength it is.

Reason #2 - umbra is not uniform, as many overly simplified diagrams show.

 

In reality, it's a gradual change of color, starting from bluish (this is sometimes not noticeable, if the atmosphere is poopy), to very dark orange-red (hue and lightness depending on the poopiness of the atmosphere).

As you've said, you have to be right there at the center for the light intensity of the ring to be low enough to really see the color in it. It's similar to looking at a low power incadescent bulb filament. The light it gives is obviously cold (around 3000 K) but the fillament is white because it's so damn bright it saturates those cells where it's focused at our retina.

 

Still, even if you were at the exact center of an umbra on lunar surface, and Earth's atmosphere was proper poopy, you would see a brilliant orange-red ring (dominantly orange), and you could see planets and brightest stars, but I really really doubt you'd be able to see other stars and especially artificial lights on Earth. They're very, very dim.

Edited January 25, 2019 by lajoswinkler

[YNM]

1 hour ago, lajoswinkler said:

poopy

you mean like sooty ?

[Green Baron]

1 hour ago, YNM said:

you mean like sooty ?

Many kinds of aerosols. It was mentioned that volcanoes, cloud cover, unspecific moisture, dust over desert/arid regions and continent wide effects over densely populated areas have their share in it. The state of the lower atmosphere (the troposphere to be exact) contributes more to the colouring and brightness than for example the stratosphere. Which is not surprising, the troposphere is the densest part and the place where weather occurs.

Edited January 25, 2019 by Green Baron

[sevenperforce]

3 hours ago, lajoswinkler said:

Kaguya had two color TV cameras for taking HDTV color video. One telephoto at 15° and one at 44°.

As far as I know, it was not color processed.

http://www.kaguya.jaxa.jp/en/equipment/hdtv_e.htm

Probably a much poorer dynamic range than human eyes.

3 hours ago, lajoswinkler said:

And yes, we'd notice red only if we're standing near or at the center of umbra.

Reason #1 - color we perceive depends on the amount of photons, too. Intense light will be white, no matter what wavelength it is.

Reason #2 - umbra is not uniform, as many overly simplified diagrams show.

As you've said, you have to be right there at the center for the light intensity of the ring to be low enough to really see the color in it. It's similar to looking at a low power incadescent bulb filament. The light it gives is obviously cold (around 3000 K) but the fillament is white because it's so damn bright it saturates those cells where it's focused at our retina.

Still, even if you were at the exact center of an umbra on lunar surface, and Earth's atmosphere was proper poopy, you would see a brilliant orange-red ring (dominantly orange), and you could see planets and brightest stars, but I really really doubt you'd be able to see other stars and especially artificial lights on Earth. They're very, very dim.

Yeah, seeing artificial lights on Earth was clearly artistic license. I'm not sure about stars. If I was far, far better at math than I am (or had a few hours to devote to it), I could take the cross-sectional volume of Earth's atmosphere tangent to the lunar-facing disc and solve the Rayleigh cross-sectional scattering equation to determine the scattering angle and attenuation for visible-spectrum light at the lunar distance. This would give apparent magnitude of scattered solar insolation which would tell you how many stars would be visible.

[cubinator]

On 1/25/2019 at 10:01 AM, sevenperforce said:

 

Yeah, seeing artificial lights on Earth was clearly artistic license. I'm not sure about stars. If I was far, far better at math than I am (or had a few hours to devote to it), I could take the cross-sectional volume of Earth's atmosphere tangent to the lunar-facing disc and solve the Rayleigh cross-sectional scattering equation to determine the scattering angle and attenuation for visible-spectrum light at the lunar distance. This would give apparent magnitude of scattered solar insolation which would tell you how many stars would be visible.

Apollo astronauts could see stars in broad daylight as long as they weren't looking at the Moon's surface. I'm sure it would be better than during a solar eclipse on Earth.

[lajoswinkler]

19 hours ago, cubinator said:

Apollo astronauts could see stars in broad daylight as long as they weren't looking at the Moon's surface. I'm sure it would be better than during a solar eclipse on Earth.

Only if they would wait for minutes with their gold plated visor off, and if nothing was illuminated anymore (like the helmet edges).

But there was simply not enough time to stargaze.

Eyes aren't fast enough to respond just like that to a sudden switch from a blindingly illuminated surface to starlight. Sure, Venus, Jupiter, brightest stars like Sirius, Antares, etc. That's pretty much it.

[Green Baron]

The unadapted human eye has around 10 good old exposure values of dynamic range. If i set it into relation to the exposure times of the bright full moon to it entering the umbra (10) then we are at the edge of what the eye can do without adaptation. The full moon on earth overshines most but the brightest stars. I can imagine that on the lunar surface without an atmosphere and everything being lit the contrast is much sharper and the surface reflection may overshine nearly all of the stars. One would probably have to enter the shadows and wait a while to actually see stars. Adaptation broadens the dynamic range to ~16ev (there may be individual differences).

Adaptation of the eye from a normally lit scene to a starlit night takes around half an hour.

 

Edited January 27, 2019 by Green Baron