BBC article suspecting NASA is manipulating the colors, page 2

I almost hate to get involved with this, because it is detracting from the real substance of this thread... but I believe in this site's credo to "deny ignorance", and there's plenty here that needs to be denied.

Originally posted by mikromarius
0.17 the gravity on Earth. That is just as good as nonexisting. There should have been quite a lot of fuzz.... Or in other words. What uses 1 second to fall from one altitude to the ground on Earth, would use about six seconds to reach the ground on the Moon.

Looks to me they are falling down pretty much quicker.....

One-sixth of the gravity of Earth is nowhere NEAR "just as good as nonexisting".

What you are neglecting to take into account is that on Earth, the primary thing that slows down falling objects (instead of having them continue to accelerate to higher and higher speeds) is air resistance. The Earth has a relatively dense atmosphere, while the Moon's atmosphere is truly close to non-existent (much more than its gravity is.)

Air resistance leads to the concept of "terminal velocity". For small particulates like dust, or large-scale objects like feathers with a high surface area, terminal velocity is quite slow. That's why dust falls much more slowly than, say, cannonballs do on Earth.

That means that dust kicked up into the air on Earth reaches terminal velocity quickly, and falls at a constant speed. The air is helping to hold it up.

In a near-vacuum like the Moon, there is almost no air resistance, so you don't get the same "terminal velocity" effects... dust accelerates faster and faster towards the surface as it falls. Thowing dust high on the Moon will mean that the dust will fall back down much faster than on Earth, and each particle will land back down at ground level typically going much faster on the Moon than on Earth.

That's not an intuitive expectation that humans have, because we don't tend to do a lot of work in near-vacuum with things like particulates.

Having a higher gravity on Earth does not compensate for having a much more limited "top speed"... imagine comparing two cars:

Car #1 (the sporty blue-and-green model) can accelerate so hard that every second, it could go 22 MPH faster than the second before... but it has a top speed of only about 3 miles per hour, let's say.

Car #2 (the dingy gray one) accelerates such that it only goes about 3.5 MPH faster each second than the last, but there is no practical top speed.

Which car wins a race of any reasonable distance? Car #2, of course, because it only takes a fraction of a second before Car #1 hits top speed and goes no faster. Meanwhile, Car #2 goes roaring by, even though it has an acceleration only one-sixth of Car #1.

Those speeds are reasonable representations of dust trying to fall on the Earth (Car #1) versus trying to fall on the Moon (Car #2). The top speed matters MUCH more than the acceleration in this case.

One of the missions demonstrated the vacuum on the Moon nicely with a "hammer and feather" experiment... drop both objects at the same time, and they both fall at the same rate on the Moon... not an experience that is familiar to humans, where the atmosphere gives a low terminal velocity to the feather.

In order to descend down from orbit in nearly zero gravity (0.17%) you need quite a lot of jet power to slow down the vessel.

This may be the heart of your problem with "nearly non-existent". You are confusing 0.17 with 0.17%. They are NOT the same thing at all. They are different by a factor of 100.

0.17% can, in many cases, be reasonably called "close to zero". But 0.17 is a substantial fraction.

Let's say you go to dinner, and the bill is $36. What is a reasonable tip? $6.00 is a pretty decent tip, and I don't know of any reasonable person who would compare $6.00 to $36.00 and say that the $6.00 may as well be zero.

That $6.00 tip is about 0.17 of $36.00

How much would the tip be on a $36.00 meal if you use 0.17%? It's about six cents instead of six dollars.

Six cents can be reasonably called "nothing" when compared to $36.00. It's only one part in 600.

3000 lbs of thrust against a sandy surface and no trace from it afterwords? That's not science, that's a miracle my friend....

It's not like there is "no trace"... the problem is with the assumption that the dust would have been deep. The lack of atmosphere ensures that the dust doesn't stay suspended in mid-air as it does on Earth... precisely because there is no air (to speak of) for it to be suspended in!

0.17%. Repeat that 100 times and think about how much lighter they would have been.

Don't bother, because that is a grossly inaccurate number... you are erroneously mixing the decimal fraction with the percent sign.

Instead of repeating it 100 times, multiply it by 100. That's what you need to do in order to make the number reasonably accurate.

In the future, I'd appreciate it if you'd use a moon-hoax related thread for the location to post deniable ignorance like this, instead of this thread, which should remain focused on the NASA logo showing in the so-called "color" photos being put out in press releases.

To the only on-topic point you seem to have made:

It appears that everything blue in the pictures are "more reflective at near-IR ranges". How they manage to do that by simply putting a tinted film before the camera with the Sun as the only light source is quite strange in the first place, unless their camera is infact an IR camera, registering infra red radiation.....

You should use Kano's fine thread about NASA not altering Mars photo colors to educate yourself a bit on how CCD cameras and filters work.

The camera registers LIGHT, not colors. The way that the camera can produce "color" images is to put a filter in front of it that filters out all frequencies EXCEPT the one that you are interested in.

In this case, the use of an infrared (~750 nm) filter with a 20 nm bandpass means that the only light that gets to the camera for an L2 shot, is light that is in the infrared range. All of the other frequencies are filtered out.

Sunlight has a HUGE range of light frequencies in it, including infrared. For a blue shot, you use a blue filter, and likewise for green. If you want to show the component of red light that humans can see in your picture, you should take a shot with a filter that is close to the human red response range of ~575 nm. That is an L4 filter for the Rovers.

When you combine a human-red, green, and blue shot, you can produce a picture that's pretty close to what a human sees.

When you substitute an INFRARED filter instead of a red filter, you get pictures that are "off", because humans don't see in infrared. The only way that the picture can be even CLOSE to accurate in the red channel, is if everything in the picture looks equally as bright at ~750 nm as it does at ~575 nm or so.

The color composites produced by NASA show that this isn't true... not only for the lander itself, but for the terrain as well.

When NASA color-balanced pictures of the rocks Sushi and Sashimi for the January 19th press release, using filters L4-L5-L6, we see that a human-vision picture of the terrain is much more sandy-yellow than the dark orange / reddish-brown pictures that NASA has put out with their L2-L5-L6 shots.

It's not really that surprising that different objects will have different levels of brightness when you examine them at different frequencies that are off by a whopping 150 nm.

To see just how "far apart" the L2 infrared filter is from the L4 (red-orange) filter, consider that 150 nm difference is enough to take a nice blue of 480 nm and compare it to a fairly deep red at 630 nm.

That's not off by "just a touch"... the similarities of the names red and infrared mask just how far apart in human-visible-spectrum terms we are talking about.

It's not off by a touch... it's off way-to-Hell-and-gone.

That's why I've been pointing out how wrong-headed I consider it to be for NASA to be constructing almost all of their so-called "color" pictures using L2-L5-L6, when L4-L5-L6 is the obvious and clear choice that should be used.

As far as "human blue" is from "human red"... that's how far apart the frequency gap is between the L2 filter and the L4 filter.

Of course the "color" pictures are wrong when trying to show what humans would see... they aren't building them using red data that is anything close to human-like.

Is that a conspiracy? Hell, I don't know... and frankly, don't care. Their motivations aren't my prime concern here. I just want NASA to "do it right", instead of doing it wrong and then coming up with excuses to justify doing it wrong.

[Edited on 1-27-2004 by BarryKearns]