# Questions tagged [time]

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

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1 vote
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### Calculating local solar time with python ephem library

I was learning to calculate local solar time with ephem. I must admit, unit conversion between radians, hours and days, which are all represented by a float in the ...
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1 vote
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### How can we see black holes collapse if time inside the event horizon is infinite?

My understanding is that if you fell into a black hole, i.e. crossing the event horizon time would be speed up infinitely fast. This means I could see my whole galaxy die, new blackholes develop and ...
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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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1 vote
109 views

### Earth’s rotation speed vs rate of lunar cycle

Hypothetical Question If the earth’s rotation slowed down to align to the lunar cycle so that the orbital period began and ended at the same lunar phase, what other things would result? For example, ...
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### Calculation of Terrestrial and Universal time scale difference, ΔT

$\Delta$T is defined as the 'measure of the cumulative effect of the departure of the Earth's rotation period from the fixed-length day of atomic time'. I tried to calculate $\Delta$T corresponding to ...
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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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### Time in 0 gravity points

If being close to a supermassive body like a black hole makes time pass more slowly for us than for an observer from a point of view with a weaker gravitational field, if we get to be at a point in ...
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### How to determine sidereal time just looking at the picture?

I have this picture: I need to determine what sidereal time it is (in hours), or how long has it been since the upper culmination of the point of the vernal equinox. How can I do that?
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### Daytime length and sunrise / set cardinal directions

Let me illustrate the question with an example. On Feb 2nd 2022, the sun rises in Los Angeles at cardinal direction 110 and sets in direction 250 (according to timedate website). This means that the ...
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### How long is the sunrise (or sunset) on North (or South) Pole? [duplicate]

I wonder how to calculate the duration of the Sun crossing the line of the horizon on equinox on Pole. For equator I used this formula: $t = \frac{2 \times p}{\cos(\phi) \times u}$, where $u$ - is ...
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1 vote
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### How to calculate the local time of sunrise and azimuth of rising point of Sirius?

I know that right ascension equals to $6^h45^m$ and declination equals to $-16°43'$. I need to calculate local time of sunrise and azimuth of rising point of Sirius on 23 of September for an ...
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### Local mean time & Solar Noon

Is local mean time supposed to represent actual sun movement? Does 12pm on local mean time (not clock time), mean that the sun is on meridian or solar noon? I understand LMT means 1 degree for 4 ...
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### Conversion of seconds since J2000 epoch Terrestrial Time to UTC time

A recent question on Space Exploration mentioned that Planet Labs provides public ephemerides for their satellites here. I believe this provides a very valuable resource for testing different orbital ...
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### Pendulum clock correction

I'm trying to solve this task: The pendulum clock was transported from the Earth's equator to Antarctica (in the vicinity of the southern geopole) for scientific experiments. Estimate the pendulum ...
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### Equation of time with arbitrary eccentricity and obliquity

I'm working on an on-line app to show the Equation of Time for arbitrary eccentricity and obliquity of the Earth's orbit. It looks good for small eccentricities and obliquities: but for bigger ones ...
1 vote
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### Would a Jovian calendar be based on the Jovian sidereal year or tropical year? [closed]

According to many places online, Jupiter's tiny axial tilt makes it have no seasons, and its huge size eliminates any variance possible due to its orbital eccentricity. All these considered, what ...
1 vote
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### Is the information about space we have old? [duplicate]

As we know light has a definite speed i.e. $c=299792458$ m/s so it takes some big time to travel from distant galaxies, right? So I always wonder about the big telescopes and big space companies ...
1 vote
159 views

### J2000 conversion to Position of date

Having spent an inordinate amount of time comparing the LBR values of Meeus (Astronomical Algorithms 1998) vs. ELP82B (Chapront's ELP82b Fortran Program) I have figured out the data set I'm using is ...
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### Why is planet visible very good in a specific time of the year?

I'm trying to solve this task: Why do periods of good evening visibility of the planets usually come in winter and spring, and morning ones - in summer and autumn? Could somebody please explain what ...
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### When the difference between the dates of old and new style becomes 14?

I'm trying to solve this task: In the twentieth century, the difference between the dates of the old and the new style was 13 days. From what date on the new style will this difference be 14 days? I ...
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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.)
56 views

### When could solar eclipse happen in a way that Sun's disk is diminishing from below?

I'm trying to solve this task: During a solar eclipse, an observer noticed that the diminishment of the Sun's disk began directly from below. Where and when could this be? Concerning "where&...
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### What is the concept of wormholes? [duplicate]

My main queries for now I guess: What is the theory behind wormholes? What is the possibility and likeliness of their existence based on scientific analysis, not conspiracy theories? What is the ...
1 vote
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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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### I'm 8 hours from Greenwich, why is my sidereal time 10 minutes different from theirs?

In order to write and run the script in this answer I typed "Greenwich sidereal time right now?" into google (or at least tried to) and got two numbers. Greenwich sidereal time was 09:51:07 ...
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### How can you determine the date using nothing but a star chart from the day and the time?

I'm doing a science olympiad event called Reach for the Stars, and one question that I've encountered provides a star chart and time of day, and you must figure out what month of the year it is from. ...
215 views

### Why do people say travelling at the speed of light or faster is impossible? [closed]

Impossible assumes we know everything there is to know about, well, everything. There was a time when everything mad knew said that traveling faster than the speed of sound was impossible. These same ...
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### Rotation of far away and near by galaxies

Do the far galaxies rotate the same as does the milky way and the near by galaxies?
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### Synodic Day and Sidereal Day

If given the sidereal day, is it possible to derive the synodic day of Earth? If a derivation is possible, could anyone illustrate it or point me in the right direction? Wikipedia's Synodic day begins:...
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### What's the reason the Astronomical twilight doesn't have constant time? [duplicate]

What's the reason the Astronomical twilight doesn't have constant time although its degrees below the horizon (18 degrees) are constant?
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### What are the Time Zones on Mercury?

I normally post on worldbuilding, but this question is merely about facts of a planets orbit and spin. I am trying to figure out how time periods work on Mercury to possibly make a worldbuilding guide ...
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1 vote
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### On Augustus' Actual Prescription to Restore the Julian Calendar to Accuracy

I hope that I may ask this question here as I have seen some favorably received questions related to the Julian calendar on this site. From James Evans' book, The History and Practice of Ancient ...
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### What are the stages in the life of a universe?

Geological periods describe varying phases in the last few hundred million years on earth. Are there any names for the periods on a timescale 1-2 orders of magnitude greater, that is, for the stages ...
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### If it only takes 8 minutes for that light to reach the Earth, what took up most of the time? [closed]

If it only takes 8 minutes for that light to reach the Earth, what took up most of all that time to get to the Earth?
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### Calculating the Solar Day of an Exoplanet?

I am currently in the process of compiling a list of stars and their planets, given the information in the European Star Catalogue found here, but I'm struggling to find out how to calculate a planets ...
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### How accurate is the "Equation of time" (mean time to actual solar time)? And how much can it vary from the average?

At Wikipedia, they give equal values (9.87 min) for all four extremes – both troughs and both crests – caused by the obliquity of the ecliptic as seen in the graph below, where the purple dashed line ...
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### How long was a lunar month in ancient times?

As the Moon is getting farther and farther from Earth, it's natural that the time it takes to circle around our planet is going to increase, thus the month will be longer. However, I read that the ...
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### What was there before the big bang [duplicate]

we know that our universe is expanding, but we must agree to the fact that it has a limit. It just cant expand till infinity. Eventually there will be a end to time. I thought alot about this and i ...
1 vote
144 views

### Sundial terminology

My homeschoolers are studying the sun & time. We have set up a fence post to create a shadow and we are using it with experiments I found on the web to track the sun. What we cannot find is ...
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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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1 vote
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### Why does time pass faster in moon than the earth?

One of my friends said that, time passes faster in moon than the earth Why does time pass faster on the moon than on the earth?
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### How are various orbital period measured?

How are the sidereal periods and synodic periods of celestial bodies measured from earth? The usual definition of the sidereal period of a celestial body is the time it takes to complete one ...
1 vote
133 views

### Timekeeping on other celestial bodies than Earth

I have looked for months for any site capable of calculating solar altitude w.r.t an observer located on the surface of a generic celestial bodies, but with no luck as of now. Even NASA does not ...
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