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Monday, January 9, 2017

Flat Earth Follies: We should see the stars!

Flat Earth Claim


We should see the stars in NASA photos of Moon or Earth!

The Facts


This is yet another case of Moon Landing Hoaxers and Flat Earthers making false statements about things which they know nothing about.  Ask them how they determined that and you'll get something between a blank stare and a bunch of hand waving.

Truth is, they have NO idea - it's just a stupid meme they pass around.

Here is an image I took of the moon through a very nice set of binoculars I own...

Figure 1. The moon via binoculars & iPhone. 

The moon is probably actually a little overexposed here since it is losing detail in the brightest areas.  But even with that, absolutely NO STARS ARE VISIBLE at this exposure level.

Why can our eye see both but the camera can't?  First of all, a full moon will make it incredibly difficult for you to see all but the brightest stars around it.  If we put you to the test you would fail to see much of anything next to a full moon.  But a deeper answer is that your eye is actually pretty good.

A healthy human eye can see over a range of about 20 stops under scotopic vision conditions (low-light - but only about 10 stops in bright light), which means the brightest parts of the scene you see can be about 1,000,000 times brighter than the dimmest parts (that is, roughly, 2^20).  That is all 'stop' means, in this context 1 stop means the brightness has doubled.  Double that 20 times and you get just a little over 1 million times brighter.  Your eye achieves this in part because the pigments in your retina that sense the light do not have a linear response.

When a camera records 14-bit RAW format it means you could have 2^14 (or 14 stops) of range, but in practice the camera sensor may limit you further than this even though it is recording 14-bits of data it doesn't mean all 14 bits are perfectly recorded and accurate.  But there are some cameras which get pretty close to true 14 stop recording such as the Sony PMWF55, which will also cost you about $35,000 list.  I've little doubt that in the coming years we can push that to 16 bits or even 20 bits eventually (some of which already exist in limited forms).  But dynamic range also comes at a cost in terms of noise and other image quality factors.  When you care about low-light sensitivity you need a large sensor area, that means you usually sacrifice pixels for quality.  There are many other trade-offs that must be made when sending a camera into space for a specific mission.  Whoever is paying for the mission sets those parameters, for example they may need infrared sensitivity which means you aren't going to find a 4K sensor with 14 stop dynamic range in infrared.  You might only get an 8 bit sensor in this case, and it might only be 1024x1024 pixels.


So here is the problem...

The moon from Earth has an apparent brightness magnitude of about -12.5 and even the brightest star, Sirius A, has an apparent magnitude of only -1.5 (and most of the stars are much dimmer than Sirius A).  The Magnitude scale is similar to 'stops' except that 5 magnitude = 100 times brighter.  So that means that the moon is about 25118 times brighter than the brightest star or 14.6 stops.  That's just outside of the range of the best Earth-bound technology sensors -- and it usually takes a few generations before bleeding edge technology can be space hardened to use in the planning stages for a mission and then another decade before the mission is ready to fly.  So even a mission going to space today would be using 10-20 year, space-hardened technology.

So, because of the brightness range of our sensors (dynamic range) and the great disparity between the brightness of the Moon (or Earth) and the stars, it is incredibly unlikely to see stars in an image where a fully lit Moon or Earth are properly exposed.

If some Flat Earther needs to see the stars and the moon in the same shot then I recommend they fund such a mission on their own using a Sounding Rocket and see how well that works out for them.

When you DO find images of the Moon with stars in them you can almost be certain that it is a composite image of different exposures which has later been remixed.  There is a very popular technique for this called HDR Photography (High-Dynamic Range) which does exactly that, you take 2 or more images at different exposures and the software will mix those images together to give you details in the shadows and highlights that would be missing from a single image.

Conversely, there are TONS of images of stars where the Earth or Moon are way overexposed.

There are also images from ISS showing stars and a dimmer side of Earth such as ISS044-E-45215:

Image Credit: NASA ISS044-E-45215

Conclusion


The claim is completely false if not entirely disingenuous in many cases and there are plenty of images of stars from space - even some showing a dimly lit Earth.

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