# Questions tagged [time]

Questions on time, the indefinite progress of events in the Universe.

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

In physics, it always takes some time for a particle to move from rest to some speed. However, photons (light particles) accelerate instantly from zero to c. How? (A visualization would be helpful.)
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### If months are based on the moon, then why are the months longer in the Gregorian calendar than lunation?

What I have always thought / known is that: Days are based on the period of rotation of the earth. Months are based on the moon. Year is the time taken by the earth to make one revolution around the ...
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### What's the reason that we have a different number of days each month?

It always was interesting for me to understand the answer for the question: What's the reason that we have a different number of days each month? If the month is fixed on the time that the moon ...
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### How many light seconds away is the JWST?

The processing for JWST's alignment is done on Earth. How long does it take for a signal from Earth to reach the JWST?
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### Does the moon have days?

As like Earth, does the moon have a day (24 hours). If it has, how many hours are in a moon day?.
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### Why are there not a whole number of solar days in a solar year?

I've been trying to find an answer to this question for some time now, and I seem to be missing something. I understand that the rotation and revolution of the Earth are not synchronized. I understand ...
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### How can we avoid needing a leap year/second?

Given the Earth's current speed around the sun and current rate & axis of rotation, what is the best way to keep time to avoid a leap year? How many hours should we have in the day and days in a ...
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### Local Sidereal Time

I am trying to understand how to calculate local sidereal time and have found the following formula: $$\text{LST} = 100.46 + 0.985647 \cdot d + \text{long} + 15 \cdot \text{UT}$$ Here, $d$ is the ...
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### Why are the time zones calculated as 360°/24 and not 361°/24 or 360°/23.933?

Background: I'm training to be a geography teacher. Currently I have practice lessons and I'll be discussing solar time and standard time with the class. Now I stumbled over an issue to which I could ...
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### Depth of gravitational well within our local Virgo supercluster?

For simplicity we could imagine standing at the north pole so we do not have to care about how fast we are moving in relation to the gravitational field of the earth. Now calculating how much faster ...
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### Years, months, days, and ... weeks?

Why do we divide time into weeks? Is there any celestial reason why humans do this? one year: earth revolution around the sun one month: moon revolution around the earth one week: 7 days = ??? ...
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### "Official" time for other planets

I want to make clock that shows current time on different solar bodies. For that I need to know how to count time on those planets. Is there any official definition of times on other planets in our ...
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### How Soon Could a Waxing Crescent Moon Be Seen?

Question: Apart from a Solar Eclipse, How much time is needed until a Waxing Crescent Moon be seen following a New Moon? Would the time of year be significant? The Vernal Equinox + 1 Month. Could it ...
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### Sidereal times occuring twice a day question

I'm reading Practical Astronomy With Your Calculator Or Spreadsheet by Duffett-Smith and Zwart. Discussing the conversion of GST to UT, the authors mention that because the sidereal day is slightly ...
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### Discrepancy in Horizons planet ephemerides for equivalent times in TT and UTC in dates during 1969

I have recently been experimenting with JPL Horizons planet ephemerides web App, and found a puzzling discrepancy. Horizons allows to specify the time at which the planet ephemerides should be ...
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### What programs do astronomers use to ensure their observatory control computer has accurate time?

Somewhere I've seen that especially those observing asteroids, in order to provide accurate observations, use timing servers that sync to atomic clocks. What software can be used to do that?
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