Jump to content

Recommended Posts

can anyone or perhaps everyone explain to me why objects farther from the sun are colder in empty space?  I understand that on Earth, in an atmosphere, that heat is dissipated as it is generated from a fire.  However, ifn space with nothing to weaken and dissipate the infrared energy, it seems that distance from the sun wouldn't decrease the heat received as long as the object is in direct sunlight. 

Share this post


Link to post
Share on other sites

A given object will receive more light when close to the sun, than the same size object further away.

Just stand close to a heater (say, an open fire) then move further away. The heat (IR light) is spreading as it moves away from the source.

(Maybe think of a balloon. When it's small, a coin on the surface has a certain amount of rubber under it. Blow up the balloon some more, and the same coin will have less rubber under it, as it's been stretched out as the balloon expands to make the larger radius (representing further distance from sun)).

On the other hand, the energy radiated out into space by the thumb, or coin, will be pretty much the same regardless.

 

Share this post


Link to post
Share on other sites
Posted (edited)

ok. i think. so. the energy spreads out as it radiates. if you get far enough away would the light spread enough to the point that the sun would appear to have dark spots? I mean, the Apollo astronauts were said to have experienced temperatures ranging from 250 degrees in the sunlight to -250 in the shade, correct? How did the suits cope with that kind of variance in the second or two it takes to step from the sunlight into the shade of the lander?  please be patient with my ignorance.

 

 

Edited by Dumb cowboy

Share this post


Link to post
Share on other sites
10 minutes ago, Dumb cowboy said:

ok. i think. so. the energy spreads out as it radiates. if you get far enough away would the light spread enough to the point that the sun would appear to have dark spots?

Not sure why it would have "dark spots" (apart from normal sunspots). But it would just get smaller and fainter. You find photos online of the Sun taken from the space probes that have gone out to Saturn and Pluto, etc. It is a small bright dot. From further away it would look just like any other star.

Quote

I mean, the Apollo astronauts were said to have experienced temperatures ranging from 250 degrees in the sunlight to -250 in the shade, correct? How did the suits cope with that kind of variance in the second or two it takes to step from the sunlight into the shade of the lander? 

Not sure how this is connected. But those temperatures don't make much sense; the temperature of what? There is no air on the moon to provide an atmosphere with a temperature to measure. 

Anyway, it takes time for something to heat up in the Sun. Put an ice cube outside on a sunny day and see how long it takes to melt.

So the spacesuits were designed to cope with this. They were white to reflect (not absorb) light and heat. They had insulating layers. They had cooling systems that pumped water all around the inside to keep a constant temperature everywhere. And so on.

Share this post


Link to post
Share on other sites
8 minutes ago, Dumb cowboy said:

ok. i think.

 

Just to reinforce what pzkpfwsaid, the keyword is 'spreading'

4 hours ago, pzkpfw said:

The heat (IR light) is spreading as it moves away from the source.

 

Look at the diagram with a source (IR or other radiation).

The radiation starts at the centre and has no other source so moves outwards along the arrows shown.

As you move away from the centre the radius increases.

So the circumference increases.
And the arcs of circumference, labelled A, B and C increase.

But the same amount of radiation passes each arc A, B, and C in turn, between the expanding arrows.

So the same amount of radiation is spread out over a larger length of arc.

If we now scale this up to 3D so we have the surfaces of spheres can you see that the surface of each sphere is larger, the further away from the centre source you are?

 

Now a bit more technical.

 

The formula for the surface area of a sphere is   [math]4\pi {r^2}[/math]

So for each sphere the same amount of radiation is spread over an area that increases with the square of the distance.

So the strength = total amount of radiation divided by the area or the amount of radiation per square metre decreases in proportion to the inverse of teh square of the distance.

 

This is called the inverse square law.

https://www.google.co.uk/search?source=hp&ei=wGGwXIDZM8zykwWw37qwBA&q=inverse+square+law&btnK=Google+Search&oq=inverse+square+law&gs_l=psy-ab.3..0l10.1294.4078..4516...0.0..1.390.4476.0j8j4j6......0....1..gws-wiz.....0..0i131.diRc6iZ4fXY

 

insq1.jpg.eb47de728d5e1231949691044d461f39.jpg

Share this post


Link to post
Share on other sites

yes, here on Earth the ice cube melts slow because it is somewhat insulated bt an atmoshere. But standing in the sunlight at 250 degrees is a little different than 100. And you can measure the temp. of things other than air

ok, i think that makes sense. so, i was thinking of the radiation as particles.  In your diagram the arrows are getting farther apart as they grow longer.  If it was a particle stream then the intensity would drop off between the arrows, right? But behaving as a wave the energy is dispersed evenly? So, I wonder if the Big Bang is behaving the same way? And I am going to be honest, the whole concept of wave versus particle gives me headaches. I also cringe at the thought of electromagnetic waves traveling through empty space.  Now I remember why I didn't pursue physics as a career, I am not good with it but I have the same problem as the cat......curiosity.

Share this post


Link to post
Share on other sites
27 minutes ago, Dumb cowboy said:

yes, here on Earth the ice cube melts slow because it is somewhat insulated bt an atmoshere.

Vacuum is a better insulator than air! The air will warm the ice, a vacuum won't.

28 minutes ago, Dumb cowboy said:

And you can measure the temp. of things other than air

Yes, I was trying to understand what those temperatures refer to. Presumably a rack that has been in the sun for many hours compared to rock that has been in the shade for a very long time?

29 minutes ago, Dumb cowboy said:

If it was a particle stream then the intensity would drop off between the arrows, right?

That it is true. But, normally, there are so many particles that you can just think of it as a continuous stream of light (waves).

Things like the Hubble space telescope do take images of objects that are so distant that photons arrive just one at a time, and so they have to use incredibly long exposures (hours, days? I'm not sure) to build up an image.

31 minutes ago, Dumb cowboy said:

And I am going to be honest, the whole concept of wave versus particle gives me headaches.

I wouldn't worry about it too much; they are just two different descriptions of the same thing!

Share this post


Link to post
Share on other sites

Why are there at least 3 dimensions of space but only one dimension of time if space and time are the woven fabric of reality?  Why does all of space move through time in the same direction?

 

Share this post


Link to post
Share on other sites
10 minutes ago, Dumb cowboy said:

Why are there at least 3 dimensions of space but only one dimension of time if space and time are the woven fabric of reality?  Why does all of space move through time in the same direction?

Who knows. 

There is some evidence that is the only stable configuration:

600px-Spacetime_dimensionality.svg.png

From: https://en.wikipedia.org/wiki/Spacetime

Share this post


Link to post
Share on other sites
11 hours ago, Dumb cowboy said:

ok. i think. so. the energy spreads out as it radiates. if you get far enough away would the light spread enough to the point that the sun would appear to have dark spots? I mean, the Apollo astronauts were said to have experienced temperatures ranging from 250 degrees in the sunlight to -250 in the shade, correct? How did the suits cope with that kind of variance in the second or two it takes to step from the sunlight into the shade of the lander?  please be patient with my ignorance.

 

 

Already covered but I thought it would be good to reiterate some of it: the difference between maximum and minimum there is not "seconds".

The moon has a day that's about 27 Earth days long. So a rock on the surface (depending on where it is) might be in Sun for about 13.5 Earth days, then in darkness for 13.5 Earth days. It's over those time frames that the rock heats up and cools down. The idea that an astronaut is exposed to almost instant swings from max to min, when in sunlight or shadow doesn't make sense. The sun does not heat things up that fast (unless you're much closer!) and things don't lose heat that fast (especially in an almost vacuum).

I'd also point out that the Apollo landings occurred in Lunar morning to avoid the extremes of heat: A good resource - http://www.clavius.org/envheat.html

---

In terms of "dark spots", were you thinking that at some far distance you'd be "in between" rays of light coming from the sun? (Is this what you meant by "between the arrows" in your post after studiot's diagram?) Basically, there's so much light coming from the sun, at so many angles (and it's not actually a point source) that anywhere where you can see it at all, you'll not be "between" all the rays of light from it. Think of it as "bazillions" of arrows. An object will have more of those arrows hitting it when close, than when far away. But it's not going to be "between" all of the arrows.

Looking at studiot's diagram, imagine another twenty arrows between the two drawn, and imagine the arc "A" is an actual metal plate. All of those arrows would hit the metal plate. If you move that plate out as far as "C" (but keep it the same size), then some of the arrows will pass to the left and right of it (so it won't get as hot). But some will still hit it. Instead of twenty arrows, now imagine a "bazillion". Space around the Sun is flooded with light. You'll not find a place where the plate is between all of the arrows (but if you keep moving further away you'll find eventually there are so few arrows hitting the plate, that they can't be detected.)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.