APOD: Moonrise Through Mauna Kea's Shadow (2019 Mar 10)

[APOD Robot]

Moonrise Through Mauna Kea's Shadow

Explanation: How can the Moon rise through a mountain? It cannot -- what was photographed here is a moonrise through the shadow of a large volcano. The volcano is Mauna Kea, Hawai'i, USA, a frequent spot for spectacular photographs since it is one of the premier observing locations on planet Earth. The Sun has just set in the opposite direction, behind the camera. Additionally, the Moon has just passed full phase -- were it precisely at full phase it would rise, possibly eclipsed, at the very peak of the shadow. The Moon is actually rising in the triangular shadow cone of the volcano, a corridor of darkness that tapers off in the distance like converging train tracks. The Moon is too large and too far away to be affected by the shadow of the volcano. Refraction of moonlight through the Earth's atmosphere makes the Moon appear slightly oval. Cinder cones from old volcanic eruptions are visible in the foreground.

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[Ann]

This is a very nice picture!

I once saw something very slightly similar, except that the dark blue Earth shadow didn't look like a mountain peak at all, just like an opaque cloud bank. The Moon shone right through it, and it looked really weird. I pointed it out to a colleague who was walking with me, and she was so impressed when I could explain it to her.

Ann

[orin stepanek]

Amazing picture of a shadow at dusk!

[Guest]

Repeat from https://apod.nasa.gov/apod/ap031203.html

[NHcycler]

Repeat from https://apod.nasa.gov/apod/ap031203.html

Thank you so much for pointing out that this APOD is a repeat from almost 0.16 centuries ago. I'm curious as to why you found it necessary to point this out? My point is that the original APOD publication date is so long ago that many APOD fans were not even born then!

[MarkBour]

Repeat from https://apod.nasa.gov/apod/ap031203.html

Thank you so much for pointing out that this APOD is a repeat from almost 0.16 centuries ago. I'm curious as to why you found it necessary to point this out? My point is that the original APOD publication date is so long ago that many APOD fans were not even born then!

And https://apod.nasa.gov/apod/ap150503.html
and a similar photo by another photographer as the https://apod.nasa.gov/apod/ap161021.html

If anyone ever gets this shot with the Moon partially eclipsed ...

[Nitpicker]

To play devil's advocate ... one possible reason to provide links to previous APODs of the same image is that, if the previous APOD is younger than this discussion forum (The Starship) it can provide easy access to previous discussions of the image.

[D Briscoe]

I think this part of the caption is incorrect or at least misleading :

The Moon is too large and too far away to be affected by the shadow of the volcano.

The projected tip of the mountain's shadow is well above the moon, and in space I think the shadow of the Earth would be mainly below that tip's projected point. But evidently the Earth's shadow is just not large enough to overlap the Moon since there is not a lunar eclipse happening. My point about the caption is mainly that the volcano's shadow is just not projected into space at a place that would intersect the Moon, and not related to the Moon's size or distance, but mainly the Moon's location.

[alter-ego]

I think this part of the caption is incorrect or at least misleading :

The Moon is too large and too far away to be affected by the shadow of the volcano.

The projected tip of the mountain's shadow is well above the moon, and in space I think the shadow of the Earth would be mainly below that tip's projected point. But evidently the Earth's shadow is just not large enough to overlap the Moon since there is not a lunar eclipse happening.
...

Interestingly, the original 2003 APOD image shows it was taken at 5:48PM, Nov 8 local time. There was in fact a total lunar eclipse 2½ hours earlier (below the horizon) but the penumbral phase was active when the image was taken, but too faint to be seen. The penumbral phase ended at 6:20pm when the moon was roughly 7°above the observatory's horizon.

[neufer]

I think this part of the caption is incorrect or at least misleading :

The Moon is too large and too far away to be affected by the shadow of the volcano.

The projected tip of the mountain's shadow is well above the moon, and in space I think the shadow of the Earth would be mainly below that tip's projected point. But evidently the Earth's shadow is just not large enough to overlap the Moon since there is not a lunar eclipse happening.
...

Interestingly, the original 2003 APOD image shows it was taken at 5:48PM, Nov 8 local time. There was in fact a total lunar eclipse 2½ hours earlier (below the horizon) but the penumbral phase was active when the image was taken, but too faint to be seen. The penumbral phase ended at 6:20pm when the moon was roughly 7°above the observatory's horizon.

Very good!

The Earth's umbra is centered slightly (about a moon width's) below the tip's projected point due to the same tropospheric refraction that provides dark red illumination well into the Earth's umbra. Slightly (again about a moon width's) above the tip's projected point the Earth's dark umbra is a fraction of a percent darker thanks to the blocking of red sunset light by the (one latitude degree wide) island of Hawaii.

Hence, Mauna Kea's penumbral Shadow does extend out into space (just above the observed peak of Mauna Kea's umbral Shadow) such that it darkens the upper half of the Earth's umbra by a fraction of a percent out at the distance Moon. A dark total eclipse of the Moon just above Mauna Kea's shadow tip might have been measurably darker... but that didn't occur this time.

[MarkBour]

I think this part of the caption is incorrect or at least misleading :

The projected tip of the mountain's shadow is well above the moon, and in space I think the shadow of the Earth would be mainly below that tip's projected point. But evidently the Earth's shadow is just not large enough to overlap the Moon since there is not a lunar eclipse happening.
...

Interestingly, the original 2003 APOD image shows it was taken at 5:48PM, Nov 8 local time. There was in fact a total lunar eclipse 2½ hours earlier (below the horizon) but the penumbral phase was active when the image was taken, but too faint to be seen. The penumbral phase ended at 6:20pm when the moon was roughly 7°above the observatory's horizon.

Very good!

The Earth's umbra is centered slightly (about a moon width's) below the tip's projected point due to the same tropospheric refraction that provides dark red illumination well into the Earth's umbra. Slightly (again about a moon width's) above the tip's projected point the Earth's dark umbra is a fraction of a percent darker thanks to the blocking of red sunset light by the (one latitude degree wide) island of Hawaii.

Hence, Mauna Kea's penumbral Shadow does extend out into space (just above the observed peak of Mauna Kea's umbral Shadow) such that it darkens the upper half of the Earth's umbra by a fraction of a percent out at the distance Moon. A dark total eclipse of the Moon just above Mauna Kea's shadow tip might have been measurably darker... but that didn't occur this time.

This is quite interesting!

I read that the radius of the Earth's umbral shadow at the distance of the Moon is about 2.65 that of the Moon (varying +/- 0.07 radii, depending on the Moon's distance at the time). If I sketch that onto the 2003 APOD image, together with the comment that it is still just grazing the Moon, I get ...

[alter-ego]

...
The Earth's umbra is centered slightly (about a moon width's) below the tip's projected point due to the same tropospheric refraction that provides dark red illumination well into the Earth's umbra. Slightly (again about a moon width's) above the tip's projected point the Earth's dark umbra is a fraction of a percent darker thanks to the blocking of red sunset light by the (one latitude degree wide) island of Hawaii.

An interesting description. An analysis of the local circumstances show mountain's shadow points near the center of the Earth's shadow. The image below shows a partially transparent, ephemeris-generated Moon and Earth's shadow image (colored, umbra and penumbra visible) overlaid on the APOD. Here, the penumbra covers about half the moon. The dashed lines show the relative changes in altitudes for the shadows and moon without refraction. The colored overlay is anchored to the moon's position and size. Refraction is important, and accurate refractive correction for the low altitude objects is not possible here. 
 

 
Edit:

• Ephemeris calculations used the standard atmospheric refraction model as in JPL HORIZONS

• Refraction matters for shadow altitudes, not for the relative Moon / Earth's Shadow geometry

 

Hence, Mauna Kea's penumbral Shadow does extend out into space (just above the observed peak of Mauna Kea's umbral Shadow) such that it darkens the upper half of the Earth's umbra by a fraction of a percent out at the distance Moon. A dark total eclipse of the Moon just above Mauna Kea's shadow tip might have been measurably darker... but that didn't occur this time.

I don't know. Given how small the mountain is to the Earth, any illumination perturbation due to the mountain would be immeasurable. A simple estimate yields the attenuation of light reaching the moon to be of the order 10^-5.

[neufer]

Hence, Mauna Kea's penumbral Shadow does extend out into space (just above the observed peak of Mauna Kea's umbral Shadow) such that it darkens the upper half of the Earth's umbra by a fraction of a percent out at the distance Moon. A dark total eclipse of the Moon just above Mauna Kea's shadow tip might have been measurably darker... but that didn't occur this time.

I don't know. Given how small the mountain is to the Earth, any illumination perturbation due to the mountain would be immeasurable. A simple estimate yields the attenuation of light reaching the moon to be of the order 10^-5.

The umbra is lit by a 360º red ring of tropospheric sunrises/sunsets much of which is blocked by clouds and mountains.

Mauna Kea blocks the bottom half of 1º of that tropospheric ring that has an otherwise clear path from the Sun to the Moon.

[alter-ego]

Hence, Mauna Kea's penumbral Shadow does extend out into space (just above the observed peak of Mauna Kea's umbral Shadow) such that it darkens the upper half of the Earth's umbra by a fraction of a percent out at the distance Moon. A dark total eclipse of the Moon just above Mauna Kea's shadow tip might have been measurably darker... but that didn't occur this time.

I don't know. Given how small the mountain is to the Earth, any illumination perturbation due to the mountain would be immeasurable. A simple estimate yields the attenuation of light reaching the moon to be of the order 10^-5.

The umbra is lit by a 360º red ring of tropospheric sunrises/sunsets much of which is blocked by clouds and mountains.

Mauna Kea blocks the bottom half of 1º of that tropospheric ring that has an otherwise clear path from the Sun to the Moon.

I digitized the worst case elevation profile across the island of Hawai'i which includes Mauna Kea and Mauna Loa. Down to a couple hundred meters elevation, the cross-sectional area amounts to 288km². Assuming a 12km tropospheric ring, the island of Hawai'i blocks < 0.1%. Given clouds around the world, the fraction blocked would indeed increase the fraction blocked by the island. My calculation used about a 20X smaller cross-section.

Recent research sheds new light on this subject. Lowest Earth’s atmosphere layers probed during a lunar eclipse concludes that 4km to 5km is the lowest altitude range the sunlight get through the atmosphere and is limited by Rayleigh scattering. Their measurements during the Dec 2011 total lunar eclipse support a minimum altitude to be 9km to 10km for most light reaching the moon. Clouds are considered to be the dominant attenuation source preventing a lower-altitude light source. I'd say the bottom line appears to be the same. Mauna Kea's (and even the entire island of Hawai'i) contribution to lunar eclipse brightness is not measurable.

[Nitpicker]

Hawaii contributes to the lunar eclipse darkness, however.

[neufer]

I don't know. Given how small the mountain is to the Earth, any illumination perturbation due to the mountain would be immeasurable. A simple estimate yields the attenuation of light reaching the moon to be of the order 10^-5.

The umbra is lit by a 360º red ring of tropospheric sunrises/sunsets much of which is blocked by clouds and mountains.

Mauna Kea blocks the bottom half of 1º of that tropospheric ring that has an otherwise clear path from the Sun to the Moon.

I digitized the worst case elevation profile across the island of Hawai'i which includes Mauna Kea and Mauna Loa. Down to a couple hundred meters elevation, the cross-sectional area amounts to 288km². Assuming a 12km tropospheric ring, the island of Hawai'i blocks < 0.1%. Given clouds around the world, the fraction blocked would indeed increase the fraction blocked by the island. My calculation used about a 20X smaller cross-section.

Recent research sheds new light on this subject. Lowest Earth’s atmosphere layers probed during a lunar eclipse concludes that 4km to 5km is the lowest altitude range the sunlight get through the atmosphere and is limited by Rayleigh scattering. Their measurements during the Dec 2011 total lunar eclipse support a minimum altitude to be 9km to 10km for most light reaching the moon. Clouds are considered to be the dominant attenuation source preventing a lower-altitude light source. I'd say the bottom line appears to be the same. Mauna Kea's (and even the entire island of Hawai'i) contribution to lunar eclipse brightness is not measurable.

November 2003 lunar eclipse

---

.
Let's push this Umbral shadow to the left by ~3 hours such that the eclipse would actually have taken place at ~4:19UT = 6:19PM HST (after sunset). The (pre 6:19PM HST) sunset shadowing of Mauna Kea should then have affected the overall brightness of the Moon.

Now lets have sent those Ultima-Thule star occultation teams to the dark skies of Paranal and La Silla to measure the temporal eclipse brightness variation for a moon location that passes through the center of the Umbra from 3:19UT to 5:19UT (with perhaps a nearby patch of dark sky as a control).

Those teams should observe an temporal asymmetry in that patch of moon brightness around the revised 4:19UT (= 1:19AM Chile) eclipse time due in small (though measurable) part to the sunset shadowing of Mauna Kea (prior to eclipse).

[MarkBour]

Now lets have sent those Ultima-Thule star occultation teams to the dark skies of Paranal and La Silla to measure the temporal eclipse brightness variation for a moon location that passes through the center of the Umbra from 3:19UT to 5:19UT (with perhaps a nearby patch of dark sky as a control).

Those teams should observe an temporal asymmetry in that patch of moon brightness around the revised 4:19UT (= 1:19AM Chile) eclipse time due in small (though measurable) part to the sunset shadowing of Mauna Kea (prior to eclipse).

So, I'm a happy little photon who just left the Sun, headed toward the Moon. At the time of my travel, the Earth is coming into my path and rotating so that Mauna Kea is just turning into the "sunset edge" of Earth, perfectly so that Mauna Kea sticks out at its very maximum profile elongation, right as I come zipping by. Now if Mauna Kea gets in my way, I'm toast, and I cannot illuminate the Moon. But if it weren't there, and I just miss planet Earth, going through the atmosphere at a minimum altitude of 2 km above the gentle Pacific ocean, will I get to the Moon? According to alter-ego, a finding is that most every photon that gets that low into Earth's atmosphere is not going to get through. I think even from the ISS it would be very difficult to see the contour of a mountain on the edge of the Earth. As an effect that merely increases the darkness of the edge nicely timed at an ISS-sunset or ISS-sunrise, it probably would require some rather sensitive equipment focused in on the region. Any such effect would be very diffuse because of all of the scattering.

[neufer]

Now lets have sent those Ultima-Thule star occultation teams to the dark skies of Paranal and La Silla to measure the temporal eclipse brightness variation for a moon location that passes through the center of the Umbra from 3:19UT to 5:19UT (with perhaps a nearby patch of dark sky as a control). Those teams should observe an temporal asymmetry in that patch of moon brightness around the revised 4:19UT (= 1:19AM Chile) eclipse time due in small (though measurable) part to the sunset shadowing of Mauna Kea (prior to eclipse).

So, I'm a happy little photon who just left the Sun, headed toward the Moon. At the time of my travel, the Earth is coming into my path and rotating so that Mauna Kea is just turning into the "sunset edge" of Earth, perfectly so that Mauna Kea sticks out at its very maximum profile elongation, right as I come zipping by. Now if Mauna Kea gets in my way, I'm toast, and I cannot illuminate the Moon. But if it weren't there, and I just miss planet Earth, going through the atmosphere at a minimum altitude of 2 km above the gentle Pacific ocean, will I get to the Moon? According to alter-ego, a finding is that most every photon that gets that low into Earth's atmosphere is not going to get through. I think even from the ISS it would be very difficult to see the contour of a mountain on the edge of the Earth. As an effect that merely increases the darkness of the edge nicely timed at an ISS-sunset or ISS-sunrise, it probably would require some rather sensitive equipment focused in on the region. Any such effect would be very diffuse because of all of the scattering.

The Ultima-Thule star occultation teams weren't bothered much by Ultima-Thule "scattering".

The effect is diffuse because of the Sun is a large & close light source.