# Tag Info

## Hot answers tagged time

### Why does light accelerate instantaneously to c, while no other phenomena do it?

"Accelerate instantly" would imply that a photon takes many different velocities at the same point in time. In fact, it would imply that a photon takes on every velocity between $0$ and $c$ ...
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### How were sundials and moondials possible 800 years ago?

As @JohnHoltz points out in a comment, planting a stick in the ground or in a wall and watching where the shadow falls is something very easy; sundials have been known since prehistoric times. I’m not ...
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### Why are the time zones calculated as 360°/24 and not 361°/24 or 360°/23.933?

The Earth takes 23 hours 56 minutes to rotate once. But that is not relevant to most people. Sure, the stars will be in the same position again after 23 hours 56 minutes, but the sun will not be in ...
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### If months are based on the moon, then why are the months longer in the Gregorian calendar than lunation?

Ancient Egyptians and Mesopotamians came up with “administrative” calendars of 30 days, that were easier to calculate than “real” lunar months of sometimes 29, sometimes 30 days. At the end of the 12 ...
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### Does the moon have days?

The answer depends on your definition of a day. If you define a day as we usually define it in the Earth (time between the Sun is at noon or average time between sunrises, a 24 hours day in Earth), ...
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### How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

This is not so hard to do. All you really need is a bit of care, a few sticks and a convenient place to observe the sunrise or sunset. So note that there is a cycle of the year and you want to know ...
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### How were sundials and moondials possible 800 years ago?

Those 2 wheels work like a perfect sundial. No they don't. They're flat. The timespan from one hour to the next on a flat sundial varies from season to season. At the same time that that temple was ...
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### How many light seconds away is the JWST?

Almost 5.1 seconds, plus or minus around 1 second. Here's a daily plot (at midnight) of the light travel time from the JWST to the centre of the Earth, courtesy of JPL Horizons, using a script derived ...
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### What's the reason that we have a different number of days each month?

You make a great point. The reason behind the discrepancy between the dates is due to a complicated history behind it. The calendar is based on the calendar created by ancient Romans, which is based ...
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### Why are the time zones calculated as 360°/24 and not 361°/24 or 360°/23.933?

We teach the students: Sidereal day: In 23 h 56 min the earth rotates 360° Solar day: In 24 h the earth rotates 361° You should not teach your students that. You should instead teach your students ...
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### Why are there not a whole number of solar days in a solar year?

if the sun appears to be in the exact point in the sky as that time the previous solar year, This statement means the sun is at (nearly) the same position relative to the stars that it was the ...
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### How many light seconds away is the JWST?

According to NASA, the JWST is 1.5 million kilometers away, which is about 5 light seconds. For comparison, the distance to the Moon is about 1.3 light seconds, Mars ranges from about 3 to 22 minutes, ...
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### How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

It's easier than you think to notice the fraction... simply because the rounding error compounds over the years! After a good amount of years, you notice that solstices are drifting from their ...
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### Why does light accelerate instantaneously to c, while no other phenomena do it?

I am not sure this is a problem of visual communication. My incling would be to think this is a problem of language communication. The equations of relativity tell us that anything with zero rest-mass ...
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### Does the moon have days?

Defining that a day is a rotation on the axis, 1 moon day is approximately equal to 27.3 Earth days. This link on moon rotation may interest you.
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### Why are there not a whole number of solar days in a solar year?

Let‘s turn your question around: Why should they be in sync? The only mechanism that redistributes angular momentum between two celestial bodies are tidal forces (not considering general relativity ...
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### How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

The ancient Egyptians appeared to know that the year was 365.25 days. This was established by observing on what day the heliacal rising of Sirius occurred (i.e. on what day that it first becomes ...
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