[Roger Röhrig]

Roger Röhrig asked the Naked Scientists:
   
With the mission to repair the Hubble telescope finally under way, I was wondering if this incredible instrument would react to things closer at home.

Would it be able to spot the footprints left by the astronauts on the moon or can't it focus that closer or would its optic be scorched by the intense
light?

What do you think?

[syhprum]

  "Hubble's keen vision (0.085 arc seconds.)"
This equates to 500 feet at 250,000 miles,quite inadequate for viewing footprints.

See http://www.telescope-optics.net/telescope_resolution.htm [Links inactive - To make links active and clickable, login or click here to register]
 

[lyner]

The Chandrayaan-1 lunar orbiter is, apparently, able to resolve objects of 5 to 10m. Fine enough to see a landing site but no footprints.

[Vern]

  "Hubble's keen vision (0.085 arc seconds.)"
This equates to 500 feet at 250,000 miles,quite inadequate for viewing footprints.
 

Very interesting information! I was just watching a news report about the space Shuttle repair attempt for Hubble. It is supposed to improve its image resolution a hundred fold. I wonder what will be the new fine field resolution?

[Fortran]

  "Hubble's keen vision (0.085 arc seconds.)"
This equates to 500 feet at 250,000 miles,quite inadequate for viewing footprints.
 

Very interesting information! I was just watching a news report about the space Shuttle repair attempt for Hubble. It is supposed to improve its image resolution a hundred fold. I wonder what will be the new fine field resolution?

Probably one tenth of an olympic sized swimming pool, almost everthing these days seems to be compared to this new? OSSP measurement - I've heard it used twice today on two seperate news items.

[Vern]

But this OSSP unit requires another component to be meaningful. It needs to be OSSP per some distance value. []

[Fortran]

1 OSSP Per 26 miles 385 yards to keep with the same system []

[syhprum]

There is no hope that Hubble's resolution could be increased a hundredfold, assuming everything is made perfectly the resolution is determined by the size of the mirror and the frequency of the light it is operating at, Hubble is already at that limit.

[lyner]

1 OSSP Per 26 miles 385 yards to keep with the same system []

So that's an Olympic Size Galaxy, quite a long way away?

[Vern]

There is no hope that Hubble's resolution could be increased a hundredfold, assuming everything is made perfectly the resolution is determined by the size of the mirror and the frequency of the light it is operating at, Hubble is already at that limit.

It seems I remember that the CCD's of the early Hubble had a resolution of 800 by 800 pixels. They must do some tricks with those because the images we see are much more detailed.

I'm not sure what the news cast was claiming was a hundred times better. What ever tricks they use to capture images have probably improved over the last 20 years or so.

[Fortran]

There is no hope that Hubble's resolution could be increased a hundredfold, assuming everything is made perfectly the resolution is determined by the size of the mirror and the frequency of the light it is operating at, Hubble is already at that limit.

It seems I remember that the CCD's of the early Hubble had a resolution of 800 by 800 pixels. They must do some tricks with those because the images we see are much more detailed.

I'm not sure what the news cast was claiming was a hundred times better. What ever tricks they use to capture images have probably improved over the last 20 years or so.

I'm sure I remember reading that there was some redundancy in the hubble in terms of the 800 x 600 ie 0.48 megapixel - it was known that camera technology would improve thus the resolution was much smaller than a single pixel, by how
much I do not know but also remember a lot of the processing is done on board
and improvements in software algorhythms will also improve 'effective resolution'  I think I read about it in Scientific American at some point.

[chris]

I am not sure I understand "500 feet at 250,000 miles" and why this is okay for seeing footprints.

Does this mean that it can spot something 500 feet across at a distance of 250,000 miles?

How far is Hubble from the moon?

Chris

[Fortran]

I am not sure I understand "500 feet at 250,000 miles" and why this is okay for seeing footprints.

Does this mean that it can spot something 500 feet across at a distance of 250,000 miles?

How far is Hubble from the moon?

Chris

Hubble is about 242,648 miles from the moon which others (being less pedantic than I) have rounded up to 250K Miles. I think the 500 feet is either the smallest object hubble can 'see' at that distance or it is the field width of the image (ie like a picture of an object 500 feet across) in which case the smallest object would be around 12 inches, to resolve a footprint you would probably need a resolution better than 1 pixel per centimetre.


Edit: Here's a piece from Nasa on that very subject

http://science.nasa.gov/headlines/y2005/11jul_lroc.htm [Links inactive - To make links active and clickable, login or click here to register]

[lyner]

Once the Lunar reconaissance orbiter is in place the conspiracy theorists will need to step everything up a notch. But will they admit they were wrong? No, it will just involve a further layer of conspiracy.
I imagine that there was a team of set builders sent a few years ago to construct fake landing sites.

[syhprum]

The Mars orbiter,s have been able to identify the rover landing sites.

[chris]

So the field of view is 500 feet - will a footprint 1/500th the size of that field be visible? Isn't that asking a lot? Isn't that like looking at a photo of a family holiday on the beach and then being able to see a single grain of sand in one corner of the photo? Sounds like a tall order to me.

Chris

[chris]

I just read the NASA link posted by Fortran. As I suspected it says:

"There are six landing sites scattered across the Moon. They always face Earth, always in plain view. Surely the Hubble Space Telescope could photograph the rovers and other things astronauts left behind. Right?

Wrong. Not even Hubble can do it. The Moon is 384,400 km away. At that distance, the smallest things Hubble can distinguish are about 60 meters wide. The biggest piece of left-behind Apollo equipment is only 9 meters across and thus smaller than a single pixel in a Hubble image."

So it looks like a footprint is indeed beyond the scope of Hubble's resolving power.

Chris

[Fortran]

I just read the NASA link posted by Fortran. As I suspected it says:

"There are six landing sites scattered across the Moon. They always face Earth, always in plain view. Surely the Hubble Space Telescope could photograph the rovers and other things astronauts left behind. Right?

Wrong. Not even Hubble can do it. The Moon is 384,400 km away. At that distance, the smallest things Hubble can distinguish are about 60 meters wide. The biggest piece of left-behind Apollo equipment is only 9 meters across and thus smaller than a single pixel in a Hubble image."

So it looks like a footprint is indeed beyond the scope of Hubble's resolving power.

Chris

If it were possible for Hubble to photograph a footprint on the moon I'm not sure conspiracy theorists will take the word of NASA that any picture was genuine, they could suggest the pictures are 'doctored'.  The principle conspiricists have a living to make.  It is impossible to prove who made a print on the moon and when, it is up to each person to decide for themselves whether or not they believe NASA,  I once published an article which rebutted the conspiricists and since none of them could prove me wrong, it is clear the landings happened!

[Roger Röhrig]

Hello all, great replies so far for the resolution question,
especially the NASA link puts things into perspective.
But what about the brightness aspect?
I'm pretty convinced Hubble's CCD would burn up if the telescope
would be pointed directly at the Sun, but what about the Moon (or the Earth)?
Would it suffer any damage?
Would the CCD be overloaded and produce a completely white picture?

Roger

[Fortran]

Hello all, great replies so far for the resolution question,
especially the NASA link puts things into perspective.
But what about the brightness aspect?
I'm pretty convinced Hubble's CCD would burn up if the telescope
would be pointed directly at the Sun, but what about the Moon (or the Earth)?
Would it suffer any damage?
Would the CCD be overloaded and produce a completely white picture?

Roger

I'd be very surprised if there were no filters, shutters built in, even a system to close the telescope hen being maintained or possibly redirected past the sun.

As for the moon no, my understanding is that that there is almost no heat reflected just visible light so although the CCD may be saturated it is unlikely to be damaged.

Not sure how much light hits us from the moon but I'll bet it's less than 1 watt/square metre.
THats from the whole moon, now consider how much light hits the earth from a a tiny square of that
probably only a few nanowatts, (to lazy to do the sums) THe moon only looks bright beacuse of the dark background,during the day it's no brighter than sunlit cloud.

EDIT: Moonlight at earth's surface approx  1mW/M2 (1 thousandth of a watt per square meter).
THus the total light from the moon entering Hubble would be around 4.5mW  (enough power to
light a low power LED. (Hubble Mirror 2.4 Metres Radius. Nothing like enough to harm even the most sensitive CCD camera.

[Raghavendra]

ya...We can see the foot steps

[thedoc]

Listen to the answer to this question on our podcast.

[syhprum]

The danger to the cameras of direct sunlight has precluded Hubble from ever viewing Mercury

[Roger Röhrig]

Just stumbled on a gret post on "Bad Astronomy":
newbielink:http://blogs.discovermagazine.com/badastronomy/2009/05/13/ten-things-you-dont-know-about-hubble/ [nonactive]
With amazing answers to my - obviously frequently asked - Hubble questions and more surprises.

Roger

[lyner]

Taking a photo of the moon (the bright bits) is just the equivalent exposure to an object on Earth, in full Sunlight: 1/125second at f8 or thereabouts. The f number of the Hubble is not particularly low - dunno what it is exactly but it will have a fairly long focal length for its diameter.

[Bored chemist]

So the answer to the original question is "only if it were a lot closer to the moon or if the astronuats had really big feet."

[syhprum]

"The FOC (faint object camera)offers three different focal ratios: f/48, f/96, and f/288 on a standard television picture format. The f/48 image measures 22 X 22 arc-seconds and yields resolution (pixel size) of 0.043 arc-seconds. The f/96 mode provides an image of 11 X 11 arc-seconds on each side and a resolution of 0.022 arc-seconds. The f/288 field of view is 3.6 X 3.6 arc- seconds square, with resolution down to 0.0072 arc-seconds"
This was an original specification and may have been upgraded now.