Expert: Tom Whiting - 7/31/2008

Question
QUESTION: Hi Tom

Thanks for the follow up explanation. Next time I will post my follow up question using the option you said.

I have an other query about communication in Space.

When we send probes to explore outer space, they send signals in the form of radio waves back to us. These radio waves like light are electromagnetic radiations. Say if the satellite reaches the SUN and sends out signals from there, it will take eight minutes for the signals to reach earth as same as light. This delay is very small when compared to the cosmic scale.
Now, how can we explore far outer space say one light year away since the signals from the satellite will reach earth only after one year?
How we can overcome this difficulty?
Is there any other mode of communication the satellites follow, like other than radio communication?
What is the longest distance a man made satellite has reached in space?
Advance thanks for your suggestions.

/Mohan

ANSWER: Hi Mohan,
Yes, radio waves are photons at different wavelengths compared to
visible light photons, but they are all the same photon traveling
at light speed. So yes, if a spacecraft is the same distance as
the sun (1 AU) then it's radio signal requires 500 seconds (8 1/3
minutes) to reach the Earth.

We cannot overcome the delay (as you say, the 'difficulty') in radio transmissions, as nothing known is faster than light speed.
We will just have to live with it, and accept it as a physical law
of nature.
(And if we ever defied physics and found something that is faster than light, then it would also be going backwards in time too...(it has to) so that wouldn't be much help either, would it?
But under our known physical laws, nothing is faster than light which includes the entire electromagnetic spectrum from radio to gamma rays.
I know of no other form of communication other than radio, although
I have heard plans of using lasers to carry information as a laser
can encode more information, but coherent light isn't any faster
than radio signals....they are all light speed.

For longest (farthest)craft from the Earth, see
http://www.heavens-above.com
and go to SATELLITES, and punch on "Spacecraft escaping the Solar
System". I believe the Voyager I spacecraft is the farthest out,
at about 107 AU or 14.77 light-hours distant.
(A far cry from 1 ly, or nearly 5.8 trillion miles, or written out,
5,800,000,000,000 miles.)
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA USA

---------- FOLLOW-UP ----------

QUESTION: Hi Tom

That explains the situation, Thanks !
So even if we use Laser to transmit signals, still the delay will be there. Okay !
I saw in your explanation, mentioning “AU”. Is it Astronomical Unit ? Is 1AU equals distance from Sun to earth ? And also I saw you mentioning “light hours”, I understand it’s the distance light covers in one hour. Please correct me if am wrong.

Thanks again for you very good explanation and link.
/Mohan

Answer
Yes, yes, and yes. (And please see my follow up to your previous message, about the Vikings, Polynesians, and Pilgrims.

Yes, 1 AU = ~ 93 million miles, and yes, one light hour is the
distance light covers in one hour; 186,000 miles per second
times 3600 seconds/hour. You can multiply it out.
Just like one light second is 186,000 miles.
And one light year is about 6 trillion miles.

A lightyear, light day, light hour, light second, are all units
of distance....the amount of distance light travels in that time
frame.
Clear Skies,
Tom Whiting
Erie PA USA