APOD: Into the Shadow (2020 Jan 24)

[APOD Robot]

Into the Shadow

Explanation: On January 21, 2019 moonwatchers on planet Earth saw a total lunar eclipse. In 35 frames this composite image follows the Moon that night as it crossed into Earth's dark umbral shadow. Taken 3 minutes apart, they almost melt together in a continuous screen that captures the dark colors within the shadow itself and the northern curve of the shadow's edge. Sunlight scattered by the atmosphere into the shadow causes the lunar surface to appear reddened during totality (left), but close to the umbra's edge, the limb of the eclipsed Moon shows a remarkable blue hue. The blue eclipsed moonlight originates as rays of sunlight pass through layers high in Earth's upper stratosphere, colored by ozone that scatters red light and transmits blue. The Moon's next crossing into Earth's umbral shadow, will be on May 26, 2021.

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[Ann]

Lovely picture with lovely colors. And to think that all the lunar colors originate from the Earth, or more precisely from the atmosphere of the Earth, and what happens when Sunlight shines through it at different angles and different heights of the atmosphere.

In the end, I find this a fantastic picture of the shadow of the living Earth on the barren Moon, whose gray uniformity is all too obvious when the Earth's shadow has passed.

Ann

[orin stepanek]

Lovely picture with lovely colors. And to think that all the lunar colors originate from the Earth, or more precisely from the atmosphere of the Earth, and what happens when Sunlight shines through it at different angles and different heights of the atmosphere.

In the end, I find this a fantastic picture of the shadow of the living Earth on the barren Moon, whose gray uniformity is all too obvious when the Earth's shadow has passed.

Ann

[MarkBour]

This is an amazing combined sequence of images.

I'll confess that (as a person who has not much studied the aspects of a lunar eclipse) I had the following theory in my head:

• When the Earth's umbra first strikes the Moon, because of the stark contrast, the human eye, or human psyche, sees it as black on white (or gray or yellow, depending on the color we're seeing for the full Moon at that point.)
• Then, I had many times seen that as it all gets dark, the Moon takes on a reddish hue (or sometimes orange). I assumed this was always the actual hue of the darkened Moon (and had learned that the reddish light is scattered light from earth's atmosphere, bathing the Moon in a very dim shade based on the light that best passes through our skies to reach the eclipsed Moon.

So, why would the edge of the umbra appear black in this sequence? And I never suspected there was any place in the shadow that would have a blue hue!

So, what is this sequence teaching me in today's APOD ?

• Clearly, as the caption pointed out, the edge of the umbral shadow actually has a faint blue hue, and they have an explanation I'm happy to accept -- that Earth's stratosphere has a realm that actually transmits blue and scatters red, as opposed to the lower, main part of our atmosphere. I wonder if it is quite consistently there, or if it is a variable phenomenon in lunar eclipses, depending on Earth's atmospheric conditions.
• But I'm not at all sure about the seemingly black edge of the umbra in these images. Is the outer edge of the umbra actually blacker than the rest, or is it that those images had to be adjusted to much lower contrast due to the overpowering moonlight from the uneclipsed part of the Moon in those images? In other words, does that edge band appear black in the photos for the same reason I thought it appeared black to the human eye -- because of the need to lower the exposure in those images?

[Chris Peterson]

This is an amazing combined sequence of images.

I'll confess that (as a person who has not much studied the aspects of a lunar eclipse) I had the following theory in my head:

• When the Earth's umbra first strikes the Moon, because of the stark contrast, the human eye, or human psyche, sees it as black on white (or gray or yellow, depending on the color we're seeing for the full Moon at that point.)
• Then, I had many times seen that as it all gets dark, the Moon takes on a reddish hue (or sometimes orange). I assumed this was always the actual hue of the darkened Moon (and had learned that the reddish light is scattered light from earth's atmosphere, bathing the Moon in a very dim shade based on the light that best passes through our skies to reach the eclipsed Moon.

So, why would the edge of the umbra appear black in this sequence? And I never suspected there was any place in the shadow that would have a blue hue!

So, what is this sequence teaching me in today's APOD ?

• Clearly, as the caption pointed out, the edge of the umbral shadow actually has a faint blue hue, and they have an explanation I'm happy to accept -- that Earth's stratosphere has a realm that actually transmits blue and scatters red, as opposed to the lower, main part of our atmosphere. I wonder if it is quite consistently there, or if it is a variable phenomenon in lunar eclipses, depending on Earth's atmospheric conditions.
• But I'm not at all sure about the seemingly black edge of the umbra in these images. Is the outer edge of the umbra actually blacker than the rest, or is it that those images had to be adjusted to much lower contrast due to the overpowering moonlight from the uneclipsed part of the Moon in those images? In other words, does that edge band appear black in the photos for the same reason I thought it appeared black to the human eye -- because of the need to lower the exposure in those images?

I believe that a photometrically consistent image would have as its lightest pixels newly exposed material on the uneclipsed Moon, and as its darkest pixels the center of maria in the fully eclipsed Moon. So yes, I think the processing of the shadow edge represents a non-linearity. If you follow a single pixel near the limb it goes from bright to dim and then its brightness increases again towards totality. That doesn't seem realistic. That said, while photometrically inaccurate, it perhaps gives a better representation of the visual experience than a more accurate processing flow would achieve.

[neufer]

Into the Shadow

Explanation: Sunlight scattered by the atmosphere into the shadow causes the lunar surface to appear reddened during totality (left), but close to the umbra's edge, the limb of the eclipsed Moon shows a remarkable blue hue. The blue eclipsed moonlight originates as rays of sunlight pass through layers high in Earth's upper stratosphere, colored by ozone that scatters red light and transmits blue.

Space Shuttle Endeavour appears to straddle the stratosphere and mesosphere in this photo. The orange layer is the troposphere, where all of the weather and clouds which we typically watch and experience are generated and contained. This orange layer gives way to the whitish Stratosphere and then into the Mesosphere. (The shuttle is actually orbiting at more than 320 km in altitude, far above this transition layer.)

---

The weak 650 nm electronic Chappuis absorption band of ozone
ABSORBS STRATOspheric RED LIGHT turning the ISS stratospheric sunset into a white band.

Single Rayleigh SCATTERING of nitrogen/oxygen molecules makes both our sky blue and turns the ISS MESOspheric sunset into a BLUE band. Ozone scattering has nothing to do with the blue moon