How Long Does It Take To Phone Home?
Light from the sun travels towards the earth and other objects
at a rate of 300,000 km. per second. or more than 7 times around the earth
in a second! 
At
that rate it takes sunlight a mere 8 minutes to get to earth compared to
the light of the next nearest star to earth, Proxima Centauri, which
is so far away that it takes light 4.3 years to reach us from there.
In fact the term light-year refers to the distance that light can travel
in a year - 1 Light Year is 9.46 x 10 12 [9,460,000,000,000]
km or 1 Light Year is 5.91 x 10 12 [5,910,000,000,000]
miles. No spaceship can travel that fast yet! You can experiment
with seeing how long it would take to travel to some places in the universe
at various rates of speed using this site: Astronomical
Differences.
Light
is not the only form of electromagnetic radiation traveling through space.
For instance we get ultraviolet and infrared rays from the sun as well
as visible light. There are other types of radiation traveling throughout
the universe from stars, pulsars, quasars, and galaxies far, far away.
Radio signals are one type of waves that can be detected by large radio
telescopes such as those used by the National
Radio Astronomy Observatory which has a site at Green
Bank, WV. Whether the radio signals are natural from pulsars
or manmade from space probes and satelites, they all travel at the same
rate as light - 300,000 km. per sec. You are going to calculate some
times and answer some questions about possible communication within the
solar system because scientists must be able to send and receive messages
from space craft. If colonies are ever established on the moon or
on distant planets, how long would it take for messages to be delivered?
Using scientific notation, the table below lists the average distances
to the planets as you found in another part of this lesson. They
have all been expressed as a number times the 8th power of ten. (i.e. 0.58
x 108 or another way of expressing that on a computer is 0.58
x 10e8. The "e" means exponent. The expanded form of this number
would be 58,000,000. The speed of light could be expressed as 3.0
x 10e5 km.
| Planet |
Mercury |
Venus |
Earth |
Mars |
Jupiter |
Saturn |
Uranus |
Neptune |
Pluto |
| distance - km.x 108 |
0.58 x 10e8 |
1.1 x 10e8 |
1.5 x 10e8 |
2.3 x 10e8 |
7.8 x 10e8 |
14.0 x 10e8 |
29.0 x 10e8 |
45.0 x 10e8 |
59.0 x 10e8 |
Using the speed of light and the distances above calculate how many seconds
it will take light to travel from the sun to teach of the planets.
You may round your answers to the nearest second.
Mercury _________, Venus _________, Earth _________,
Mars _________, Jupiter _________,
Saturn _________, Uranus _________, Neptune _________, Pluto _________
Since radio waves also travel at 3.0 x 10e5, now you can calculate how
long it would take in seconds to send a radio message from earth to each
of these planets. Remember that you are going from earth to the planets,
not starting at the sun as you did above! (to the nearest second)
Mercury _________, Mars _________, Jupiter _________,
Pluto _________
If you were actually sending a message and waiting for a response the times
would double. Take your answers from above and calculate the time
to both send and receive a message back and then change it into minutes.(to
the nearest tenth of an minute)
Mercury _________, Mars _________, Jupiter _________, Pluto
_________
Which of those above would take more than an hour? List them and
tell how many hours. (to the nearest tenth of an hour)
How long would it take to send a message to a star that was 8 light-years
away? ____________
And how long would it take to get the answer back? _____________