
Can you see the flag on the Moon with a telescope? - jaybol
http://www.rocketroberts.com/astro/flag_on_moon.htm
======
showerst
Interestingly, one thing we DID do that's observable from earth is to put an
array of retroreflectors onto the moon, so that we can bounce a laser off of
it.

[https://secure.wikimedia.org/wikipedia/en/wiki/Lunar_Laser_R...](https://secure.wikimedia.org/wikipedia/en/wiki/Lunar_Laser_Ranging_experiment)

My sample size of moon landing skeptics (1) didn't dispute that we've been to
the moon, he just didn't believe that we did it in 1969, but if you do run
into a skeptic this is pretty good evidence that we made it there eventually,
or at least requires the conspiracy to be much more involved =).

~~~
ck2
But so few photons come back, sometimes I wonder if the measurements are
within a margin of error or reflection off atmosphere.

Mythbusters did a good episode on the moon skeptics though.

~~~
gus_massa
If someone say honestly that they _receive_ the photons coming from the moon,
then they _must_ get a number of photons that is bigger than the error margin,
preferably a few times bigger than the error margin. If it is smaller they
can't be sure that it is not some noise.

The data about these measures is hard to find. But after some googling the
best data I could find are in
<http://physics.ucsd.edu/~tmurphy/apollo/highlights.html> . It it possible to
make some estimations from the graphs.

There are three sets of three graphs. They are very similar, so let's see only
the first one.

In the first graph there is a dark line in the center that shows that there
are more photons coming at the expected time, than before or after that time.
The signal is easy to see, but it is difficult to get any numerical values
from this graph.

From the second graph it is possible to read some numerical values. Each bar
shows the number of photons that arrive in a 100 ps interval. They have
probably a Poisson distribution, but for simplicity let's approximate that by
a Normal distribution.

Before the peak, there are approximately 10 +/- 10 photons coming every 100
ps. (These values are estimated from the graph with a lot of zoom, I can't be
very sure about them. The values seem to be scattered between 0 an 20, so I
assume that the average is ~10 and the standard deviation is ~10.) These are
the photons that come from others sources. So if no mirror is present in the
moon, or the laser dos not have enough power, then this is the expected value
during all the experiment.

At the peak, there are approximately 400 photons in the same time interval.
The difference between this value and the average of the first values is like
40 times the standard deviation. So it is almost impossible that they get
these peaks by a random chance. For example, the probability to get a value
that is bigger than 5 standard deviation is less than 1E-6, for 10 standard
deviation it is less than 1E-23, and for 40 standard deviation it is almost
almost 0. And they get not only one, but 8 intervals with more than 100
photons.

After the peak, they get more photons than before the peak for technical
problems. I see something like 20 +/- 20. Whit these numbers, the chance of a
400 photons peak is bigger, but still almost 0, but I think that the correct
way to do the estimations is using the first values.

The third graph is an auxiliary measure with an earth based mirror to get the
dispersion caused by the system.

The analysis in the web page is more elaborated. They estimate the shape of
the mirror and use the data from the third graph to explain the shape of the
peak.

------
weichi
Two things.

1\. The 3.5 mile figure is for resolving the _stripes_ on the flag, not for
seeing the flag. If you just want to see the flag, an aperture diameter of
around 400 m is required.

2\. The "Dawes Limit" is just presented with no explanation. It ultimately
comes from the fact that the achievable angular resolution of an aperture of
size D, using light with wavelength lambda is lambda/D. So if you were willing
to work at 10 nm, then the aperture size goes down by a factor of 50 (of
course working at 10 nm has it's own set of problems).

~~~
teamonkey
I was concerned by the lack of Wiki-fu about the Dawes Limit on this forum,
but it turns out that the wikipedia page is very sparse. This is a more
detailed page on the subject and explains where the Dawes Limit comes from.
<http://en.wikipedia.org/wiki/Angular_resolution>

------
jorgem
Yes. If you are on the moon, you can see the flag with a telescope.

------
rimantas
But when you get closer…:
[http://www.nasa.gov/mission_pages/LRO/multimedia/lroimages/a...](http://www.nasa.gov/mission_pages/LRO/multimedia/lroimages/apollosites.html)

~~~
dwc
If any of you are _really_ interested, <http://lroc.sese.asu.edu/> has more
than the NASA pages. We've also imaged Russian lunar rovers. :)

------
ck2
I would guess things have changed a little with the newest technology?

The correct answer might now be "not with the naked human eye" (through an
optical telescope).

It is only recently possible to correct atmospheric distortion by having a
computer project a laser through the atmosphere and measure the change in
realtime and adapt for it (adaptive optics).

[http://en.wikipedia.org/wiki/File:Laser_Towards_Milky_Ways_C...](http://en.wikipedia.org/wiki/File:Laser_Towards_Milky_Ways_Centre.jpg)

Also, the increase in CCD densities have become enormous in the past few
years. So it might be possible to make a matrix that could resolve the flag in
the near future.

The stereo telescope method they mention at the end has also been improved
recently if I remember reading correctly and they have robotic telescopes that
can pull this off.

ps. the James Webb Telescope that's going up in 2014 will have 6 times the
collection area of the Hubble, so maybe that will be able to do it ! It looks
like it's right out of Star Trek:

<http://en.wikipedia.org/wiki/File:JWST_people.jpg>

~~~
borism
it just isn't physically possible to resolve a flag on the surface of the moon
with anything less than 3.5 mile diameter telescope. The technology used can't
help much with physically impossible things!

~~~
mrb
It is perfectly possible to resolve a (6-foot) flag with a telescope.

The article states "the Earth's atmosphere is never steady enough to allow
resolution below about _one arc second_ for most locations". But according to
the European Southern Observatory one can do 1000x better:

"With AMBER on the Very Large Telescope Interferometer (VLTI), the astronomers
were able to see details on the scale of _one milli-arcsecond_ , corresponding
to being able to distinguish, from the Earth, the headlights of a car on the
Moon." \-- <http://amber.obs.ujf-grenoble.fr/spip.php?article154>

Therefore a 6-foot-wide flag ("headlights of a car") would be visible as 1 or
2 pixels with the VLTI, which is made of four 8.2 meter reflectors.

I presume the actual flag left by the astronomers was somewhat smaller, so one
would need a tad better telescope, but certainly not something with a "3.5
mile diameter".

Upvote me. HN readers need to be educated :-)

~~~
borism
yes, but the article explicitly defines "flag being visible" as stripes of the
US flag being visible. for that you would need a tad better than 6-foot
resolution.

~~~
mrb
Fair enough.

On a side node, the VLTI should be able to produce a 2x2 or 3x3 pixel image of
one of the russian or american lunar landers (14-foot wide). It would be a
cool thing to accomplish to demonstrate the resolution of the VLTI...

------
cschmidt
> What could Hubble see on Earth if it were to be aimed at the Earth? ... > it
> can be shown that Hubble could just make out something that is 5.56 inches
> wide on Earth.

I found that quite odd. I've always heard that spy satellites could read the
headline on a newspaper. Why would the Hubble be so much worse? That makes the
math in the article a little suspect.

~~~
tokenadult
The claims about what spy satellites can see have been exaggerations at least
since the 1960s. They are still exaggerations today. I hope everybody knows
that the "satellite" view on Google Maps is from conventional aerial photos
(taken from airplanes) as you zoom in.

~~~
mturmon
To tell the truth, you don't know that they are still exaggerations.

It is a fact that the NRO has been working on optical interferometers, and
deployable reflectors, and probably has launched at least one.

------
RyanMcGreal
> Therefore it is _not even close_ to possible to see the Flag on the Moon
> from Earth with telescopes available today.

How ... _convenient_.

/fusionparanoia

------
borism
_The only method that could be used to (in theory) see something as small as
the Flag on the Moon would be to use two optical telescopes set (for example)
1000 miles apart. This would easily provide the required resolution, the huge
problem however is combining the images from both telescopes in such a way to
realize the resolution. As far as I know right now that technology is not
available. Even if the technology was available, the unsteadiness of the
Earth's atmosphere would likely render the method useless._

I've read about this method being used a lot in radioastronomy. But how does
one proceed to use it in optical astronomy?

And surely if it is possible to algorithmize this it wouldn't be a problem to
write a program that will take care of such "technology"?

~~~
cletus
The method you're referring to is called _optical interferometry_ [1] (well,
interferometry in general but optical for visible light obviously). Great
strides have been made in this department in recent years and I believe it's
been used for exoplanet detection [2].

[1]: <http://en.wikipedia.org/wiki/Optical_interferometry>

[2]:
[http://en.wikipedia.org/wiki/Astronomical_optical_interferom...](http://en.wikipedia.org/wiki/Astronomical_optical_interferometry)

~~~
borism
mkey, but one will have to build 3.5+ mile wide optical interferometer...

largest being built right now is 400m wide:
[http://en.wikipedia.org/wiki/Magdalena_Ridge_Observatory_Int...](http://en.wikipedia.org/wiki/Magdalena_Ridge_Observatory_Interferometer)

------
gcb
A: No.

------
bloodbought
Slightly off topic...

I don't consider myself a conspiracy theorist but in my opinion the demeanor
of Armstrong and crew during the Apollo 11 press conference is indicative of
deception.

Have a look: <http://www.youtube.com/watch?v=-RcKLAo62Ro>

~~~
burgerbrain
_"I don't consider myself a conspiracy theorist..."_

Do conspiracy theorists ever?

~~~
bloodbought
Fair enough. To clarify, I don't subscribe to really any of the doctrine or
ideas presented by the conspiracy "mainstream." I do believe American
astronauts have walked on the moon during six individual Apollo missions. I
also believe in the instance I referenced previously, that those three men are
lying about something.

~~~
ars
I watched it, and see no deception, just nervousness mixed with formality.

Also a little regret knowing they will never go back.

~~~
ddbeck
"Also a little regret knowing they will never go back."

Wow, I had never thought of that aspect of the Apollo program. It's a little
sad that of the 22 people to orbit the moon, land on the moon, or both, it
appears just four of them ever made a subsequent space flight.

~~~
mturmon
From Buzz Aldrin's bio on wiki:

"In March 1972, Aldrin retired from active duty after 21 years of service, and
returned to the Air Force in a managerial role, but his career was blighted by
personal problems. His autobiographies Return To Earth, published in 1973, and
Magnificent Desolation, published in June 2009, both provide accounts of his
struggles with clinical depression and alcoholism in the years following his
NASA career."

