Time measurement outside solar system?

Question

The sun is used to determine and measuring time in our solar system. What if we were to travel outside the solar system i.e. to interstellar space, or other galaxies and other celestial bodies (out of our solar system). How would we keep a tab on time then?

Answer 1

Units of time are actually quite arbitrary.

Their relationship to astronomical features is historical:

it's what people used when counting rotations and revolutions of the planet were the best tools to hand. Nowadays, they are legacy values: the "true" units are other things that happen to be feasible to measure using modern tools (wavelengths of light, resonances of atoms), with particular values chosen and scaled to match the old values for continuity.

And other units derived from them were purely matters of arithmetical convenience. Factors of 12 and 60 were common because they make it easy to do arithmetic in thirds and quarters, and when doing fractions, they reduce easily. So a value like a "second" is absolutely and utterly arbitrary; it applies to outer space exactly as well as it does here.

The second's arbitrary value is the fundamental unit of the metric system, that that's what scientists use to communicate with each other. The numbers can be scaled for their convenience: as long as they're labeled, one system is as good as any other. (Especially with computers to do the work.)

Astronomers try to measure rotations and revolutions of distant bodies, and when speaking of them in public they might use "day" or "year" to help people visualize it. But when speaking to each other, they know what the technical terms mean, and avoid the ambiguity of layperson speak.

So in the end, it's all just "seconds", scaled up or down. It may be converted to something else for public consumption or even with each other, but when it comes down to brass tacks they find it's easiest to all use the same unit, even if it's completely arbitrary.

(It is worth noting that some physicists use a rather unfamiliar set of units call "natural units", under which important constants like the speed of light and the pull of gravity work out to precisely 1. These are convenient when you're pushing around equations, but require a fair bit of effort to translate into clocks and rulers when you want to build an actual experiment.)

Another approach can be Through an atomic clock.

Modern atomic clocks use atoms to determine the passing of time. So you would measure it using that.

For example 1 second is defined as --- the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom This mean that if you can make a laser shine on a ceasium 133 atom and by counting the periods of the light emitted you will now how many seconds have passed.

As a interesting side note sins our orbit around the sun is not constant it is sometimes necessary by the scientific community to prolong a year by a second or so every now and then to make clocks match the moment of the earth. There called leap seconds

Answer 2

We would use a clock.

Actually, we don't use the position of the sun for determining time. The apparent position of the sun doesn't change with enough regularity. Events on the Earth, such as Earthquakes, can change the length of a "day". The spinning of the Earth is a good clock, but not the best.

The best clocks use the frequency of light emitted by an atom (often a caesium atom). This frequency is very stable, far more stable than the Earth. If we were far from the sun, we could still use a clock to provide accurate timekeeping.

The clock would record local time, which would not keep in sync with Earth time if the clock were moving relative to Earth, due to relativistic effects.

Whether we would still use "days", "months", "years" etc is speculation. (and hence off topic) I'll note that our internal body clocks work best in a cycle of about 24 hours.

Answer 3

The sun is used to determine and measuring time in our solar system.

Correction: The Sun (or more precisely, the Earth's rotation) was used to determine and measuring time in our solar system. Over two thousand years ago, keeping time via the appearance of the Sun was known to be problematic. The Babylonians, Egyptians, and other ancient cultures knew this. This became problematic with the invention of accurate clocks about four hundred years ago. Kepler argued that a clock rather than the position of the Sun was the proper way to keep time. Clocks and sundials disagree by as much as 16.5 minutes due to the equation of time.

Over a hundred years ago, the Earth's rotation rate was found to be less even less rock solid than thought. The second was redefined to be based on the Earth's orbit about the Sun as opposed to the Earth's average rotation rate. This, too, proved unreliable as we developed ever more accurate timekeeping devices.

Nowadays we keep time with atomic clocks. To keep time in sync with the rotating Earth, people worldwide observe the difference between the smoothed Earth rotation rate and what atomic clocks tell us. We occasionally have to introduce a leap second to maintain the fiction of a solar-based concept of time. For example, the last minute of 2016 will be 61 seconds long. (Leap seconds are a plague upon humanity. Leap minutes or leap hours would have been a better solution. Ask google. Or ask me. I'm currently dealing with a leap second problem in real life. It is a massive PITA.)

Even atomic clocks are a bit problematic. A minor problem is that some atomic clocks are more accurate than others. Even more problematic is that even the most accurate of atomic clocks won't keep time with one another due to the ever changing shape of the Earth. While our last ice age ended about twelve thousand years ago, the Earth has not quite recovered from the effects of the kilometer-plus thick sheets of ice that formerly covered parts of the Earth. The ongoing post glacial rebound affects the rate at which different atomic clocks tick.