neufer wrote: ↑Tue Mar 12, 2019 2:15 pm
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.
Mauna Kea Lunar Eclipse 2003 - Ephemeris Overlay_2.jpg
- 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
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