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View Full Version : Are the Voyager and pioneer spacecrafts in (near) darkness now?



Denis12
2006-Feb-10, 09:10 PM
The Voyager and Pioneer spacecrafts are far away from us at this moment ,outside the aphelion of pluto. And the sun must look very dim at that distance ,but are they in a dim daylight like a full moon here on earth? Or are they in a full darkness? Denis.

Grey
2006-Feb-10, 09:19 PM
Looking here (http://www.heavens-above.com/solar-escape.asp), I see that the magnitude of the Sun from these craft ranges from -16.7 to -17.5 (and it's really cool that there's a place to look these up that easily!). The full Moon has a magnitude of -12.7, so that even from the farthest, the Sun is about 40 times brighter. Certainly far from full daylight, but more like twilight than night time, I'd imagine.

ToSeek
2006-Feb-10, 09:31 PM
I think that would still be bright enough to read comfortably, like a 100-watt light bulb 12 feet away.

Grey
2006-Feb-10, 10:10 PM
I think that would still be bright enough to read comfortably, like a 100-watt light bulb 12 feet away.Hmm, let's see. The Sun puts out about 3.9 x 10^26 watts, so that's an increase of 3.9 x 10^24 in power over the 100 watt bulb. The most distant (Voyager 1) is at a distance of 98.5 AU, or 4.8 x 10^13 feet, or an increase in distance of 4 x 10 ^12 in distance. Given the inverse square law, that gives us a result of about 0.25, so it would be more like a 25 watt bulb at 12 feet. For the nearest (Pioneer 11), it would be about twice that bright at 71.4 AU. Pretty close, ToSeek. Did you actually work it out, and miss a factor, or were you just guessing, and managed to hit that close? Either way, that would still certainly be enough to read by.

grant hutchison
2006-Feb-10, 10:32 PM
A jigger factor of 5 or 6 is necessary because the Sun puts out more of its power as visible light than a light-bulb does. A 6000K black-body (as an approximation to the Sun) puts out about 95 lumen/watt; a 100W incandescent bulb only about 17 lumen/watt.

Grant Hutchison

ToSeek
2006-Feb-10, 10:41 PM
Hmm, let's see. The Sun puts out about 3.9 x 10^26 watts, so that's an increase of 3.9 x 10^24 in power over the 100 watt bulb. The most distant (Voyager 1) is at a distance of 98.5 AU, or 4.8 x 10^13 feet, or an increase in distance of 4 x 10 ^12 in distance. Given the inverse square law, that gives us a result of about 0.25, so it would be more like a 25 watt bulb at 12 feet. For the nearest (Pioneer 11), it would be about twice that bright at 71.4 AU. Pretty close, ToSeek. Did you actually work it out, and miss a factor, or were you just guessing, and managed to hit that close? Either way, that would still certainly be enough to read by.

I'm borrowing from some stuff I worked out in response to another one of Denis's questions, involving how bright Mercury would be if Earth were in Mercury's orbit with Mercury revolving around it at the Moon's distance.

Denis12
2006-Feb-10, 10:43 PM
I think that it is very freezing cold there,and they are going further and further away from us. And i am curious what their fate is,are they going to another star with a possible solarsystem? Or will they going through the emptiness with some stars around them......or is it possible to turn them and get them back to earth. Can you explain these things? Thanks.

Romanus
2006-Feb-11, 12:59 AM
^
Unless we bring them back, they're never coming back, and there's no way for them to turn around.

They will pass close to several stars over the course of the next million years or so, but "close" in this case means maybe 1-3 l.y. The chances of them passing say, within 50-100 AUs of any star in the next several million years is extremely small. Interestingly though, they won't stray very far from the Sun's orbit around the Milky Way, perhaps no more than a kiloparsec or so; they just don't have enough speed.

Lord Jubjub
2006-Feb-11, 01:57 AM
My mind boggles at the vastness of space when I try to visualize that.

ZaphodBeeblebrox
2006-Feb-11, 04:55 AM
My mind boggles at the vastness of space when I try to visualize that.
Try This (http://www.noao.edu/education/peppercorn/pcmain.html) ...

I Did a Version of it, When I Helped Out, With a 3rd Grade Class ...

I Put Earth at 4 Feet, And Stuck The Kid Holding Pluto, at The Top of a Big Hill!

:dance:

tony873004
2006-Feb-11, 07:19 AM
Interestingly though, they won't stray very far from the Sun's orbit around the Milky Way, perhaps no more than a kiloparsec or so; they just don't have enough speed.
Interesting. Is that from your own intuition, or did you read that somewhere? I tend to think that excluding a very close (hence, improbable) passage to another star, that you are right, at least in timescales of low billions of years.

Romanus
2006-Feb-11, 10:13 AM
^
I was waiting for someone to ask that. Actually, I had the good fortune of copying a brief article out of a 1979 issue of "Astronomy" (IIRC--unfortunately, the article information was off the copy page, and I neglected to write a bibliographic entry for it), wherein a scientist calculated the future path of Pioneer 10 through the next 500 million years, based on what was then known about the Milky Way and the Sun's orbit. The graphic had the Sun at its center, and illustrated Pioneer 10's motion relative to the fixed Sun. The orbit was "epicyclic", basically spiralling slowly outward from the Sun, but no farther than 600-700 pc. I took the same premise and extended it outward to 1000 pc, a guesstimate due to the Voyagers' higher heliocentric velocity. The article also stated that the chance of Pioneer 10 passing within 10,000 AU of any star during this time frame was extremely low.

Grey
2006-Feb-13, 03:21 PM
A jigger factor of 5 or 6 is necessary because the Sun puts out more of its power as visible light than a light-bulb does. A 6000K black-body (as an approximation to the Sun) puts out about 95 lumen/watt; a 100W incandescent bulb only about 17 lumen/watt.Ah, of course you're right. Good catch.

Disinfo Agent
2006-Feb-13, 05:46 PM
Pale blue dot. (http://spider.ipac.caltech.edu/staff/jarrett/sagan/pale_blue_dot.html)

ZaphodBeeblebrox
2006-Feb-13, 06:23 PM
Pale blue dot. (http://spider.ipac.caltech.edu/staff/jarrett/sagan/pale_blue_dot.html)
What'll Be, Really Neat ...

Is When we Leave, The WHOLE Solar System ...

"See that White Dot, Over There, That's Everything!"

:eek:

Duane
2006-Feb-13, 10:35 PM
I'm a little confused DA, what your post was meant to represent, in the context of this discussion. Would you be so kind as to elaborate?

Disinfo Agent
2006-Feb-13, 11:33 PM
Certainly.


The Voyager and Pioneer spacecrafts are far away from us at this moment ,outside the aphelion of pluto. And the sun must look very dim at that distance ,but are they in a dim daylight like a full moon here on earth? Or are they in a full darkness? Denis.If Denis12 clicks on the link I posted, he will see what the Sun looks like to Voyager 2, or at least what it looked like a while ago.

Duane
2006-Feb-13, 11:40 PM
Thanks. In future, a brief comment would be appreciated, if for nothing else, to avoid confusion.