Questions tagged [time]
Questions on time, the indefinite progress of events in the Universe.
154
questions
3
votes
2answers
219 views
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 ...
2
votes
1answer
144 views
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
1answer
56 views
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
2answers
796 views
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
0answers
70 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 ...
3
votes
1answer
84 views
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 ...
0
votes
1answer
69 views
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 ...
29
votes
6answers
10k views
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.)
2
votes
1answer
53 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&...
0
votes
0answers
31 views
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
1answer
118 views
Understanding the constant 6.697374558 when finding GMST
I'm trying to understand the constant 6.697374558 mentioned in this question:
The Astronomical Almanac gives an expression for approximate mean
sidereal time, in hours:
$$\mathit{GMST}=6.697374558+0....
3
votes
1answer
77 views
Task about equinox and upper culmination
I'm trying to solve this task:
At what local time is the point of autumn equinox at its upper culmination three weeks after the vernal equinox?
I think it has something to do with the sidereal day (...
1
vote
0answers
48 views
How to determine time when a photo of star trails was taken?
I was asked to define a time (most likely the month) and location of the picture below.
I hope I understood it right that it is the south pole, because we don't see a Polar star in the middle. ...
1
vote
0answers
25 views
How to determine how often a planet's center will be collinear with its moon's?
Expanding on the question: Let's say I have a planet orbiting some star (earth-like, sun-like, for the sake of example). If this planet has two moons, M1 with orbital period of 30 earth-days and M2 ...
1
vote
1answer
73 views
Understanding the difference between local time and local sidereal time
I am currently attempting to understand different systems of telling the time: particularly, distinguishing local time (LT) from local sidereal time (LST). I understand that they often differ; despite ...
1
vote
1answer
103 views
Energy conservation of the universe
I have tried to derive an equation for the total energy of the universe.
I have found that,
$$E(t)= \delta\dot a(t)^2a(t)\Omega(t)$$
Where $\delta$ is just a positive constant, a(t) is the scale ...
25
votes
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 ...
0
votes
1answer
100 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 ...
3
votes
3answers
271 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. ...
-5
votes
3answers
135 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 ...
7
votes
2answers
467 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?
3
votes
1answer
137 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:...
0
votes
1answer
61 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
votes
2answers
184 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 ...
1
vote
1answer
96 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 ...
8
votes
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 ...
0
votes
1answer
217 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
votes
1answer
46 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 ...
2
votes
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
votes
1answer
102 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 ...
0
votes
0answers
46 views
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
2answers
107 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 ...
11
votes
7answers
4k views
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 ...
1
vote
1answer
90 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?
2
votes
0answers
55 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 ...
1
vote
2answers
118 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 ...
5
votes
3answers
845 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 ...
6
votes
3answers
1k 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. ...
1
vote
1answer
72 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 ...
0
votes
0answers
66 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 ...
2
votes
0answers
75 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 ...
1
vote
2answers
335 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:
...
3
votes
1answer
1k 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 ...
1
vote
1answer
188 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.
6
votes
2answers
389 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 ...
3
votes
1answer
192 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, ...
1
vote
2answers
1k 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 ...
2
votes
2answers
160 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 ...
1
vote
1answer
68 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? ...
4
votes
1answer
159 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?
