Question

I have a question and I hope its not too silly.

Are there standard (optical) cameras on space probes, and, if so, how do
they see the planets?

OK, like I said, its silly. I know that there are all sorts of
infra-red/etc instruments on spacecraft that pick up all kinds of radiated
materials from a planet. But some of the still photos I've seen appear to
be plain old regular photos. What I want to know is, if this is the case,
where does the light come from? I mean, when taking pictures of Uranus, for
example, is there really enough light from the sun to fully illuminate the
surface? Or does the aperature on the camera stay open for long periods of
time to collect a lot of light? Or do the atmospheres of the planets
themselves give off some sort of illumination?

Don't laugh. I really am curious!

In article , User wrote:
Are there standard (optical) cameras on space probes...

Well, "standard" is pushing it -- they tend to be custom designs -- but
yes, many of the images you see published are taken in ordinary visible
light. The colors are sometimes exaggerated or otherwise off, because the
image has been computer-enhanced or the spectral bands of the camera don't
match those of the human eye, but otherwise the image is roughly what you
could see from the same vantage point. Typically you would have to use a
small telescope, mind you, because the cameras have those built in.

...But some of the still photos I've seen appear to
be plain old regular photos. What I want to know is, if this is the case,
where does the light come from? I mean, when taking pictures of Uranus, for
example, is there really enough light from the sun to fully illuminate the
surface? Or does the aperature on the camera stay open for long periods of
time to collect a lot of light?

Yes, the light is sunlight. It's a lot dimmer than it is here, but it
still illuminates things well enough. They *do* often use relatively long
exposures, and the cameras for outer-planet spacecraft often have fairly
large apertures to gather more light (in the same way that large
binoculars give you a brighter view at night here).

Or do the atmospheres of the planets
themselves give off some sort of illumination?

No, apart from occasional lightning and auroras (which have sometimes
been photographed).
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

"User" wrote in message ...
What I want to know is, if this is the case,
where does the light come from? I mean, when taking pictures of Uranus, for
example, is there really enough light from the sun to fully illuminate the
surface?

Yes.

Food for thought:

At Pluto's orbit, sunlight is about 1/1600th as strong as it is at
Earth's orbit. That might sound dim, but that's about 1000 times
brighter than the Earth's night time full moon.

At Uranus, sunlight is 4 times as strong as it is at Pluto, equivalent
to about one 4-watt (well, 3.5W) light bulb per square meter. You
could light up an interior room pretty well with 4 watts per square
meter. That's like a 35-40W bulb lighting up a 10ft x 10ft bedroom.

Or does the aperature on the camera stay open for long periods of
time to collect a lot of light?

That, too, I think.

Mike Miller, Materials Engineer

Henry Spencer wrote:
Yes, the light is sunlight. It's a lot dimmer than it is here, but
it still illuminates things well enough.

Yes. Saturn is easily visible to the unaided eye from Earth. Uranus
is visible under good conditions. Neptune can be seen in a small
telescope or good binoculars. Sunlight is about a thousand times
dimmer on Neptune than on Earth, but that's *still* brighter than
the average indoors. The eye has a very high dynamic range.

Even where the Pioneer and Voyager probes are now, far beyond the
orbits of Neptune and Pluto, the light is *still* bright enough to
easily read by. (If there were anything to read there, and anyone
to read it.)
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.

I have a question and I hope its not too silly.

There are no such things as silly questions (almost).

Are there standard (optical) cameras on space probes, and, if so, how
do they see the planets?

Well, "standard" is probably not the right word, as far as I know, all space
probe cameras so far has been more or less tailor-made. But it's a camera
employing largely the same techniques as any off-the-shelf digital camera.

OK, like I said, its silly. I know that there are all sorts of
infra-red/etc instruments on spacecraft that pick up all kinds of
radiated materials from a planet.

What's radiated is usually not "materials" but rather energy, usually in the
form of electromagnetic radiation (radio waves, microwaves, infrared light
[heat], visible light, ultraviolet light or X-rays).

But some of the still photos I've
seen appear to be plain old regular photos.

They are. A photo is a detection of the visible light radiated from an
object.

What I want to know is,
if this is the case, where does the light come from? I mean, when
taking pictures of Uranus, for example, is there really enough light
from the sun to fully illuminate the surface?

Depends on what you mean by "fully" :-) But yes, images taken by space
probes show us what the planets look like in reflected sunlight.

Or does the aperature
on the camera stay open for long periods of time to collect a lot of
light?

Good guess! Out by Uranus, or even worse, Neptune, the Sun looks so small,
that it's hard to distinguish it from all the other stars. Now, I don't know
for how long time Voyager 2 exposed the images of e.g. Neptune, but I don't
think it was taken on 1/500 sec.!

Or do the atmospheres of the planets themselves give off some
sort of illumination?

Probably not in visible light. I believe Jupiter and Saturn give off some
UV- and X-rays of their own, and Jupiter radiates some in the radio bands as
well, but that's it.

Hope that cleared up a few things :-)

/steen