Need help explaining: NASA images of Earth from 2017 eclipse show different shadow sizes

[Patrick Gonzalez]

This is the first time I create a thread on this site. I've read the posting guidelines as required and I'm doing all I can to stay within those guidelines.

https://svs.gsfc.nasa.gov/12698

: NASA and its partner’s satellites had a unique vantage point to watch the eclipse. Several Sun-watching satellites were in a position to see the Moon cross in front of the Sun, while many Earth-observing satellites – and NASA’s Lunar Reconnaissance Orbiter, which typically images the Moon’s landscape – captured images of the Moon’s shadow on Earth’s surface.

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As seen from NOAA's DSCOVR and GOES-16 and NASA's LRO, the shadow seems to be the size of the entire continental United States while in ISS and high-altitude balloon footage it seems to be just the umbra. I vaguely remember a flat-Earther using this footage as "proof" that NASA was faking footage from those satellites (even though both DSCOVR and GOES are from NOAA) but that was months ago and I don't remember which YouTube channel was it.

My guess is that the images from DSCOVR and GOES are darker while the ISS and high-altitude balloon images have a higher exposure and different color settings. This could definitely be the case for the LRO images as it's designed to take pictures of the Moon (i.e. gray and dark imagery). As I know very little about photography I don't know. Would some of you please help me with this? Thanks. :^)

 

[Mick West]

As seen from NOAA's DSCOVR and GOES-16 and NASA's LRO, the shadow seems to be the size of the entire continental United States while in ISS and high-altitude balloon footage it seems to be just the umbra.

The umbra (region of total eclipse) is quite small. If you are at relatively low altitude and can see the umbrae, then you can't really see the edge of the penumbra, because it's over (or near) the horizon.

 

[Jon Adams]

Hi Patrick:

One would also need to know what the dynamic range of the imager is, as the chewy dark center is a lot dimmer than the bright Earth. Like if you were inside a black-walled house with a photo hanging on the wall next to an exterior window through which the sun was streaming, while your camera was pointed out the window at the sun, and you wanted to make out the detail of the photo.

While I have no personal data for the brightness of the sky during a total lunar eclipse, according to information posted at this site, the umbral magnitude of a particular 2018 total lunar eclipse was predicted to be magnitude 1.3, and the full sun is about magnitude -26, so that's 27+ magnitudes, which is about 7E10 difference. (5 astronomical magnitudes equals a difference of 100 in brightness.) That's about a illumination difference of 70 billion to one, which would require an imaging sensor to have a heck of a lot of dynamic range. Because of this, it's quite possible the sensor gain was set to not wash out the the normal Earth brightness, and so the umbral center would be way way lower than the sensitivity of the sensor. It'd just be black.

Trying to estimate the size and darkness of the umbra from an image like this, using a sensor not purposed for this, is not very useful.

Cheers and 73 - Jon N7UV

 

[Vaeltaja]

I made a small recording with space engine to show this phenomenon from space with different exposures:


Source: https://streamable.com/usdq3z