Light Travel Time: Seeing the Past?

In summary: This is because the distance between the Earth and Mars changes so much that it would take too long for a command to reach the spacecraft and have any effect.
  • #1
Bammitzcam
1
1
Hey guy,
I was browsing YouTube and watched a speed comparison video and it was just different races timed. I noticed that light speed took 12 minutes to reach Mars from earth. So I thought this

If we look at Mars through a telescope or what ever, Does that mean we are actually looking back in time? We are not actually there but does it mean we are seeing past events (assuming there was an event lmao)
Excited to see the responses. This is my first ever science post because I'm 14
 
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  • #2
Yes indeed, we are always looking at how things were in the past. When you look at the moon you are seeing it as it was 1 second ago. When you see the Sun you are seeing it as it appeared about 8 minutes ago. The nearest major galaxy (Andromeda Galaxy) to our own is over 2 million light-years away, so if you ever see it through a telescope you are seeing it as it appeared more than 2 millions years ago.

Also, I've edited the title of this thread to something more appropriate for the topic.
 
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  • #3
Hi.
Yes light travels at known speed, so when you see a distant object. what you see is what it was like in the past.
For far away galaxies it can be billions of years
 
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  • #4
:welcome:
If you want to learn even more about the "oddities" of time (aka the basis of Special Relativity :oldbiggrin:), I suggest searching "Time Dilation" and the "Einstein Clock" on google.
 
  • #5
Comeback City said:
:welcome:
If you want to learn even more about the "oddities" of time (aka the basis of Special Relativity :oldbiggrin:), I suggest searching "Time Dilation" and the "Einstein Clock" on google.
 
  • #6
Bammitzcam said:
Hey guy,
I was browsing YouTube and watched a speed comparison video and it was just different races timed. I noticed that light speed took 12 minutes to reach Mars from earth. So I thought this

If we look at Mars through a telescope or what ever, Does that mean we are actually looking back in time? We are not actually there but does it mean we are seeing past events (assuming there was an event lmao)
Excited to see the responses. This is my first ever science post because I'm 14
That 12 min light travel time to Mars is about the average. Since the actual distance between Earth and Mars changes due to their different orbits, this time can vary from a bit over 4 min to almost 21 min.
Since this delay also applies to radio signals, this is why we can't control the rovers on Mars in "real time". If we send a command to the rover to perform an action it will take from 8 to 41 min before we will see the result of that command on the rover. The same is true during landing operations. By the time we could find out that there was a problem and tried to send a correction, the landing will have already either succeeded or not.
 
  • #7
Janus said:
The same is true during landing operations. By the time we could find out that there was a problem and tried to send a correction, the landing will have already either succeeded or not.

Indeed. Also, the video of the JPL team during the landing sequence was wonderful (landing occurs about an hour into the video). For the OP, if you watch the video, you may notice that they don't send any commands to the spacecraft during the landing sequence. All of it is pre-programmed in.
 

1. What is light travel time?

Light travel time refers to the amount of time it takes for light to travel from one point to another. It is a fundamental concept in physics and is used to measure distances and understand the behavior of light.

2. How does light travel time allow us to see the past?

Light travel time allows us to see the past because light takes time to travel from an object to our eyes. This means that when we look at objects that are far away, we are actually seeing them as they were in the past, as the light from those objects took time to reach us.

3. Can we see events that happened millions of years ago with light travel time?

Yes, we can see events that happened millions of years ago with light travel time. This is because light travels at a constant speed of approximately 300,000 kilometers per second, so the light from objects that are millions of light years away has taken millions of years to reach us, allowing us to see what those objects looked like millions of years ago.

4. How does light travel time affect our understanding of the universe?

Light travel time plays a crucial role in our understanding of the universe. It allows us to study distant objects and events, providing insights into the history and evolution of the universe. It also helps us measure the distances between objects and determine their true age.

5. Is there a limit to how far back in time we can see with light travel time?

Yes, there is a limit to how far back in time we can see with light travel time. This limit is determined by the age of the universe, as light can only travel a certain distance in a given amount of time. This means that we cannot see events that occurred before the universe was formed, which is estimated to be around 13.8 billion years ago.

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