Questions tagged [time]

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

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3
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3answers
112 views

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. ...
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3answers
5k views

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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1answer
93 views

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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3answers
101 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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2answers
463 views

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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1answer
90 views

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:...
2
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1answer
85 views

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 ...
2
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0answers
49 views

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 ...
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1answer
58 views

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?
3
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2answers
124 views

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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1answer
78 views

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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3answers
252 views

Is this a coincidence?

The smallest distance probed in any experiment so far conducted is $10^{-18}$m and the largest distance we can have is the radius of the universe, nearly $10^{26}$m. The ratio is $10^{44}$. In ...
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1answer
133 views

Validity of ephemeris time

In the wikipedia article for ephemeris time as first adopted in 1952, it does not explain clearly how or why it was superseded. For example, it reads: In 1976 the IAU resolved that the theoretical ...
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1answer
1k views

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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1answer
153 views

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?
2
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1answer
42 views

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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3answers
143 views

If FTL travel is possible, can I look back in time to a younger earth? [closed]

For this question assume that. We found a way to go faster than light. I build a ship that could go faster than light and go to another planet with this ship in the span of mere hours. The ship was ...
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0answers
32 views

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 ...
2
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2answers
5k views

Space time and aging

Would a more significant curvature of spacetime relative to earth (i.e. time on jupiter) effect the aging process? Basically would you age at a slower rate? Or age faster on the moon?
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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 ...
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2answers
91 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 ...
4
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1answer
406 views

Sorting out Julian Day, Julian Date, Julian Day number, Julian Day Calendar, and Julian Day Table

In this answer I mention day number which is 1 on the first day of each calendar year (January 1) and increments to 365 or 366 on December 31 of that year. There was an edit proposed, which included ...
3
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3answers
359 views

How could time only have started with the Big Bang?

I understand that before the Big Bang time (as well as dimensions) didn't exist. But how could this be? If there was no time then nothing could change, and so time itself couldn't come into existence.
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7answers
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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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1answer
85 views

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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2answers
1k views

“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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2answers
104 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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3answers
606 views

What does BJD-2450000 mean?

In different papers I've encountered time indications in BJD-2450000. I know that BJD stands for Barycentric Julian Date, but I don't understand the meaning of the suffix -2450000. This is an example ...
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1answer
68 views

How can I correct for transit time?

I know the exact time a radio telescope detected a transient event. I also know the exact location of the telescope, and the galactic coordinates (galactic longitude, latitude) and right ascension and ...
6
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3answers
933 views

Julian Day Calculation

I'm trying to calculate the Julian Day, given a UTC year, month and date in the Gregorian calendar. I tried using the formula on Wikipedia, but that doesn't work. Consider 2010-01-31 and 2010-02-01. ...
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0answers
65 views

Does time flow in a Minkowski spacetime?

In a spacetime where the stress-energy tensor is null (no energy, no matter, no entropy), I wonder whether any motion of the variable time in the phase-space is well defined. The arrow of time, meant ...
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0answers
72 views

If time is not absolute and depends on the gravitational field, then why we keep using our own (particular) time in cosmology?

Sorry if my question is not really clear, but indeed it is not clear in my mind neither. But maybe some of you can help. Time is not absolute and can be affected by the gravitational potential. Now ...
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1answer
141 views

Why does gravity make time go slower and warp light?

I know that objects with lots of gravity are capable of warping light or slowing time (an example being a black hole). I also know this is because of the theory of relativity, but I need someone to ...
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2answers
225 views

Convert dates to julian day number in astropy?

I'm using astropy and I need to convert dates like this: 2012.06.22_17:56:15_TAI into julian day number. I tried: ...
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1answer
925 views

How much time passes in the outside universe when falling into a black hole?

If someone were to jump into a black hole, looking back at Earth, how far into the future would they see of Earth? As I understand it, time would dilate approaching infinity as you approach the event ...
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1answer
104 views

How to calculate sunrise and sunset on on a given date and location?

I have a given date at any time in future or past eg: 2016-04-23 or 2022-05-12 Now given at any location(lat,lng). How do i find the time of sunrise or sunset.
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1answer
137 views

What's a good model for the vernal equinox year? Can it increase forever?

Duncan Steel (2002) makes an interesting argument that the notion of year is (1) somewhat arbitrary and, more interestingly (2) one notion of year can increase while another decreases. His examples ...
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3answers
311 views

Why the continued obsession in measuring the year as a multiple of days?

Pick a any notion of year and any type of day measurement. Outside of history and the common cycle of day an night, why are these viewed as integrally or even fractionally commensurate? Why all the ...
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3answers
24k views

When we see the Sun, do we actually see its past?

The Sun's rays hit our eyes around 8 minutes after they are emitted from the Sun. Does this mean that the Sun that we see is always the Sun as it was some 8 minutes before? I strongly think this must ...
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4answers
1k views

Photon Paradox?

Imagine a photon reaching the Hubble Space Telescope today had originally been emitted from a star in the early universe 13 billion years ago. Einstein’s Special Relativity tells us, traveling at the ...
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2answers
301 views

How do we measure the age of the universe?

As mentioned in wiki/Age_of_the_universe, The current measurement of the age of the universe is around 13.8 billion years (as of 2015) – 13.799±0.021 billion years When my friend who is not from ...
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1answer
157 views

So, what, exactly, is a tropical period?

From timezone.com's On the Units of Time Part III: The Year February 19, 2001, by Edward Hahn: Uh, Oh…He’s Going to Ask That Question Again… So, what, exactly, is a year? @PM2Ring's comment FWIW, ...
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2answers
874 views

Is a year really 365.24 days, or is it 365.2564 days like I remember?

The NPR News item and podcast Spring Starts Today All Over America, Which Is Weird includes the following: But why isn't the time of the equinox the same each year? The short answer is that the time ...
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1answer
5k views

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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2answers
154 views

When was the longest day on record?

The Earth's rotation is gradually slowing down. It was significantly shorter in the prehistoric past, but now we need to add a leap second every few years and we've not yet had to take any back. In ...
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1answer
67 views

Encode place and date in star pattern

Disclaimer: I'm an astronomy noob You sometimes see in (B?) movies, that they infer dates from sky patterns. I was asking myself if you can encode a place and date in a mostly meaningful pattern? ...
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2answers
93 views

How can I calculate 27 tropical/solar year since my birthdate?

Let's say I was born on 27th November 1993 at 03:15:15 AM. Is there any way I can calculate exact 27 tropical cycle since my birthdate/birthtime. What date and what time it will be after exact 27 ...
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2answers
398 views

Getting Solar Noon from Sunset and Sunrise

I've seen the solar noon formula described as snoon = 720 – 4*longitude – eqtime. I'm curious if it is equally reliable within a relatively small margin of error (+-...
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1answer
156 views

How is the Gould Belt younger than the sun?

Our sun is located in the Gould Belt, a group of stars which is thought to be 30 - 50 million years old. However, the sun formed 4.6 billion years ago. Did the belt form around us?
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1answer
160 views

What is the exact time of sun stay in each zodiac every year on sidereal year duration?

I tried to reverse engineer from astro-chart times at which sun stays in a zodiac. Here is the list. ...