# Sunset-Sunrise reversal?

## Main Question or Discussion Point

Sunset-Sunrise reversal???

If you got in your airplane an hour after the sun has already set, say in North Carolina, and traveled west towards California, would you end up seeing the sun rise in the west and eventually (if you could travel fast enough and head towards China) see the sun set in the east? Please don't react to this question, rather just try and look at it from a different perspective that's all. I only ask to not be so quick to dismiss it.

## Answers and Replies

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ideasrule
Homework Helper

You will, but the plane needs to be traveling faster than Earth's rotation. For the latitude that North Carolina is at, that would be 1400 km/h. This is faster than the speed of sound, and the only supersonic passenger jets in history were the Concorde and the Tupolev Tu-144. These planes actually did travel faster than Earth's rotation, so passengers arrived earlier in the day than when they departed.

For someone flying in say a SR-71 which holds an absolute speed record of 1,905.81 knots (2,193.2 mph; 3,529.6 km/h); if they flew long enough in the direction opposite of the Earth's rotation from somewhere like NC(35° 38' 27" N / 79° 50' 35" W) would they be traveling backwards in time?

Or would time still progress forwards and the sides (i.e. west and east) where the sun sets and rises just be flipped, and if this is true, then what would account for the flip? Would east and west just be an illusion of Earth's rotation?

In mid-summer, at 34 degrees latitude (los angeles), the required ground speed would be 860 mph; a bit over the speed of sound. The crusing speed of a jet airliner is about 550 mph(airspeed). With the jet stream traveling from west to east, this won't help your east to west ground speed.

Traveling at 550 mph due east, midsummer, at greater than 58 degrees latitude would do it.

If you took a leasurely walk around the north pole would you be time taveling?

Matterwave
Gold Member

For someone flying in say a SR-71 which holds an absolute speed record of 1,905.81 knots (2,193.2 mph; 3,529.6 km/h); if they flew long enough in the direction opposite of the Earth's rotation from somewhere like NC(35° 38' 27" N / 79° 50' 35" W) would they be traveling backwards in time?

Or would time still progress forwards and the sides (i.e. west and east) where the sun sets and rises just be flipped, and if this is true, then what would account for the flip? Would east and west just be an illusion of Earth's rotation?
Oh man, I love that 40 years after Superman (the movie) came out, it's still putting these thoughts in people's minds.

The flow of time doesn't change just because the direction you travel on Earth changes. The flow of time won't even change if the entire Earth rotated the other way...contrary to what Superman would have you believe.

russ_watters
Mentor

For someone flying in say a SR-71 which holds an absolute speed record of 1,905.81 knots (2,193.2 mph; 3,529.6 km/h); if they flew long enough in the direction opposite of the Earth's rotation from somewhere like NC(35° 38' 27" N / 79° 50' 35" W) would they be traveling backwards in time?

Or would time still progress forwards and the sides (i.e. west and east) where the sun sets and rises just be flipped, and if this is true, then what would account for the flip? Would east and west just be an illusion of Earth's rotation?
A "day" is not measured based on when you see the sunrise or sunset, it is based on when a fixed point on earth sees it*. If you redefine a day or year based on your observations, you can claim (deceitfully) to be younger or older than the earth-centered measurement would have you, but it won't make you actually be younger or older.

Astronauts fly around the earth every 90 minutes, but that doesn't mean they have to shave every hour and a half, nor do they attempt to sleep in 30 minute spurts, every hour hand a half. They continue to go by a normal earth clock.

*Superman notwitstanding: That was the original definition. Today, the length of a day is simply a numerical definition/standard, but even if Superman did his thing before that definition was established, people would notice their watches and beards behaving as they had before.

Astronauts fly around the earth every 90 minutes, but that doesn't mean they have to shave every hour and a half, nor do they attempt to sleep in 30 minute spurts, every hour hand a half. They continue to go by a normal earth clock.
Interestingly instead of having to shave more often they have to shave less often. This is due to an effect known as relativistic time dilation. Although the speed of the space station is relatively slow on the cosmic scale the resulting time dilation is still measurable. http://spaceflight.nasa.gov/station/crew/exp7/luletters/lu_letter13.html

ideasrule
Homework Helper

They have to shave their beards just as often--there's no time dilation in the rest frame. If they shave every 3 days in their frame, Earth would see it as slightly longer than 3 days. That means people on Earth see them shaving more often, not less.

Ok I'll give in to it not being time travel , but what about the directions? Is it safe to assume that east and west are just illusions of earth's rotation?

Matterwave
Gold Member

No, we can define East and West as just directions on Earth like left and right so that we can talk to each other. Certainly North and South can be found using a compass. And then, we say that when you are facing North, your right is West and your left is East. This way, we can tell each other how to go places (e.g. "go North 2 blocks, then turn West"). We certainly don't tell each other "go North 2 blocks and then turn with the rotation of the Earth".

I understand how directions work. Of course we wouldn't say that. I'm ultimately getting at how east and west (and even north and south) are just constructs of the human mind. In particular, east and west were created to compensate for the way in which the sun seems to rise and set. What I want to know is, would the sun would seem to travel backwards across the sky if you were to travel in opposition to the earth's rotation? And if this were true, then, we would we be able to disregard any notion of east and west as a reality because the sun would rise in both directions. Consequently, depending on which way we saw the sun rise or set (i.e. rise east/set west, rise west/set east), north and south would flip as well. So how would Nature account for the way in which the directions seemingly flip in my frame of reference? Or does Nature only account for clockwise and counter-clockwise (which to humans, seems to be East and West), and Magnetic-North and Magnetic-South?

russ_watters
Mentor

I'm ultimately getting at how east and west (and even north and south) are just constructs of the human mind. In particular, east and west were created to compensate for the way in which the sun seems to rise and set.
No, east and west were created for the purpose of geography and defined according to the surface of the earth, not the motion of the sun. So....
What I want to know is, would the sun would seem to travel backwards across the sky if you were to travel in opposition to the earth's rotation?
As already said, yes (if you travel fast enough).
And if this were true, then, we would we be able to disregard any notion of east and west as a reality because the sun would rise in both directions.
And as also said, since east and west are directions on a map, not locations of the sun, no. Heck, you wouldn't be able to verify that the sun was going backwards unless you knew which way was really east and west! You could see the sun rise and say that direction was east, but you'd still have to look at the compass on your SR-71 to know it was backwards from how east is really defined!
Consequently, depending on which way we saw the sun rise or set (i.e. rise east/set west, rise west/set east), north and south would flip as well.
So that's also a no, except in this weired SR-71 centered reference frame that you are trying to define.
So how would Nature account for the way in which the directions seemingly flip in my frame of reference?
Nature doesn't care at all about our frame of reference nor would it care about this weird SR-71-centered frame you just created.
Or does Nature only account for clockwise and counter-clockwise (which to humans, seems to be East and West), and Magnetic-North and Magnetic-South?
Nature doesn't account for any of these things. They are all human constructs. The earth rotates the way it rotates, regardless of if humans are here to attach labels like "clockwise" to it or not.

Matterwave