PDA

View Full Version : Light years/times



mattweather
2006-Jul-16, 03:21 AM
Does anyone know the earth's time that we travelling to Mars and then back? I need to understand more about space and light years.

Van Rijn
2006-Jul-16, 04:15 AM
Does anyone know the earth's time that we travelling to Mars and then back?


I'm afraid I don't understand the question. What do you mean by "we travelling"? A spacecraft? That depends on the trajectory and velocity of the spacecraft. Light? That depends on the current distance to Mars and the (constant) speed of light.



I need to understand more about space and light years.

A light year is the distance light travels in a vacuum in one year.

01101001
2006-Jul-16, 04:53 AM
In case you think the vast distance to Mars might need to be measured in lightyears, it really doesn't. It isn't vast enough.

The radius of Mars' orbit around the sun is about 1.5 AU (http://en.wikipedia.org/wiki/Astronomical_unit). Earth's orbit radius is 1 AU. The distance between Earth and Mars varies with their positions, but can't be more than about 2.5 AU, which occurs when they are on opposite sides of the Sun.

Let's see... 1 AU is only about 1.58 × 10-5 lightyears, .0000158 lightyears.

So the maximum distance between Earth and Mars is about .0000395 lightyears. That is around 1248 lightseconds, or almost 21 lightminutes, better units perhaps.

astromark
2006-Jul-16, 10:29 AM
In the days of the Apollo missions we traveled to the Moon in approximately 72 hours. We have sent numerous space probes to Mars when the distance between the two planets is closing. So that the space craft travels the quickest path possible. Both Earth and Mars are hurtling around the sun at a blistering pace. You really do need a computer program to do all this calculating the orbital speeds the different rates of movement and mass over gravity effects of both. . . Its rocket science. I sagest that the out trip might take three months. Earth time. The return trip could take four months. Only if a quick visit landing time was to be adopted. This is complex stuff but, if the time on Mars was to be longer. then the return trip would be left to the next close approach. Two years round trip. I do not think this decision has been made yet.

mattweather
2006-Jul-17, 12:59 AM
Yeah thank guys, i really appreciated about this. It quite credible about the time differences in other places.

Kaptain K
2006-Jul-17, 06:27 AM
astromark,

...the space craft travels the quickest path possible.
No! They travel the most economical path possible (Known as a Hohman transfer orbit.)

You really do need a computer program to do all this calculating...
No, you don't! Hohman (see above) did his calculating before there were computers and programs. Robert Heinlein insisted that all orbits in his stories (written in the 40s, 50s and 60s) be accurate, so he and his wife Virginia did all of the calculating on a roll of butcher paper on a long table.