Questions tagged [time]
Questions on time, the indefinite progress of events in the Universe.
120
questions
1
vote
1answer
51 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
30 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
80 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
257 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
485 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
64 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
61 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
66 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
70 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
457 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
56 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.
5
votes
2answers
103 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
112 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, ...
0
votes
2answers
142 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
135 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
62 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
155 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?
1
vote
1answer
98 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.
...
1
vote
2answers
185 views
Does mean solar time and sidereal time sometimes indicate the same time?
I'm trying to wrap my head around the different definitions of time. Since mean solar time depends on the Sun, and sidereal time depends on the stars, and since the position of the Sun relative to the ...
0
votes
2answers
84 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 ...
3
votes
2answers
77 views
Are there predictions of the distribution of matter at the end of time
Are there any theoretical predictions or "educated speculation" by cosmologists on how matter will be distributed at very, very distant times in the future?
For example, will matter be:
agglutinated ...
1
vote
1answer
75 views
Is there a way to know the time according the moon appearance?
Is it possible know the time according to the moon location? To look at the sky at night and then determine what the time is.
1
vote
2answers
69 views
Can I use the Tokyo Skytree as clock?
After my observation today at the Skytree in Tokyo, I am wondering if this building could be used as a giant sundial?
As an aside, it would be interesting to consider how the Skytree might be used ...
9
votes
3answers
2k views
How is time defined in astronomy?
I was amazed when my teacher told me that in space, time is define as a coordinate. It means we can define something with a four coordinate system with "negative time" $-t$ as easily as we can say $-...
3
votes
0answers
57 views
Does Gravitational Time Dilation stack on top of Time Dilation caused by Velocity?
Using 1 CM from the Event Horizon of Super Massive Black Hole, SGR A, as the reference point. The particles within the accretion disk are traveling at extreme high speeds. Assume this speed increases ...
9
votes
3answers
2k views
Coordinate system for space [closed]
I am high school student, I have doubt if I have to locate a planet or any star in space, how do I locate it, because we have no perfect coordinate system, I have read in some books, that time is ...
2
votes
0answers
36 views
Syncing time for measuring the parallax of Mars
I read somewhere (I can't remember the website) that when Cassini and Jean Richer measured the parallax of Mars, they used Jupiter's (or maybe Saturn's) moons to sync their time. How was this done?
4
votes
0answers
80 views
Why does “longitude by chronometer” require first calculating latitude?
I'm studying the history of longitude and Greenwich Time, and I'm currently confused about the "longitude by chronometer" technique.
Conceptually, the method seems extremely simple. With a ...
0
votes
3answers
176 views
How can we see stars if they are hundred years of light far from the Earth?
So the right question is, is the light years counted from that second when you look up to the sky? If that so, how can we see the stars from the telescope (which I think it starts when you put your ...
2
votes
1answer
66 views
How do I calculate Allan Variance (maybe for pulsars)?
I am studying pulsar timing this summer and have come across many Allan Deviation plots that include several popular clocks alongside pulsar measurements, like this one by N. Ashby and D.A. Howe:
I ...
1
vote
0answers
46 views
What exactly is a Right Ascension clock and how was one (mounted on a telescope) used in practice, historically?
@MikeG's answer to Why does this Lowell Observatory telescope have so many knobs? What do they all do? explains that item #6 labeled in the image there (and cropped version here) is likely to be a "...
1
vote
2answers
72 views
What are some examples of routine human activity times for certain cultures/peopes that are based on the position of the sun?
What are some examples of timekeeping that are based on the height/angle/position of the sun. Two examples that come to mind are the times of the Islamic prayers times and the golden hour in ...
3
votes
0answers
66 views
Is TDB monotonic? Does it or any of its derivatives have yearly discontinuities with respect to an atomic clock?
This in-depth answer mentions that
...TDB is updated every year. As technology improves, these subtle updates change the timing of past events.
This makes me wonder...
Does this updating result ...
3
votes
1answer
103 views
Validity of ephemeris time
In the wikipedia article for epmeris time as first adopted in 1952, it does not explain clearly how or why it was supersed
ed. For example, it reads:
In 1976 the IAU resolved that the theoretical ...
8
votes
1answer
375 views
Universe is expanding, why doesn't time expand with it?
Reading this response When the universe expands does it create new space, matter, or something else? I understand Universe is not expanding like if it is stretching its space, but it is actually ...
3
votes
1answer
271 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 ...
1
vote
1answer
93 views
Is there a maximum Julian day?
I have read various discussions of the Julian day, including that on the Wikipedia, but none of these appear to define the maximum Julian day or proleptic Gregorian year in which that maximum day ...
2
votes
2answers
711 views
Difference between zone time and local sidereal time?
What is the key difference between LST and ZT?
Also, are UT, GMT and Greenwich Mean Solar Time the same?
1
vote
3answers
148 views
What orbit is the smallest or takes the least time to complete?
What orbit in our solar system would take the least time to perform 1 orbit?
What is the fastest possible orbit to complete in the universe?
0
votes
3answers
118 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 ...
1
vote
1answer
135 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 ...
2
votes
1answer
187 views
How far does the Earth travel around the Sun during each month of the year?
After reading about the Earth's orbit and how it moves faster in January than it does in July (based on its distance from the Sun), I started to wonder...
How far does the Earth travel around the Sun ...
3
votes
0answers
43 views
How did the Big Bang occured if before that there was no time? [duplicate]
I am thinking, that if the Big Bang created time, it implies that before the Big Bang there was no time (correct me if I am wrong).
My question is that, if there was no time before the Big Bang, how ...
2
votes
1answer
193 views
Determine Julian Date from Gregorian without formula
As an exercise, I am trying to calculate the JD from a given date in the Gregorian Calendar at a time given in UT. Furthermore, I want to do so from first principles without relying on any formula. ...
24
votes
1answer
4k 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 ...
2
votes
1answer
78 views
What causes random irregularities in the earth's rotation accounted for by dynamical time
I read in a book that the earth's rotation sometimes shows unpredictable irregularities(not caused by precession, nutation, tidal forces) which are accounted for using dynamical time. What would be ...
3
votes
1answer
2k views
How to convert sidereal time to local time?
I came across something that won't let me go, but no matter how much I calculate (which I do not like), it doesn't seem to work.
Also: I've used so much apps and links already to convert, but it doesn'...
3
votes
3answers
198 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 ...
0
votes
2answers
164 views
Does the Milky Way's movement through space have spacetime implications?
The way I usually see spacetime explained, it says that if you just sit still, you are moving at 0kph and so you are moving at maximum speed through time (ie. time for you is flowing at maximum speed)....
1
vote
0answers
70 views
Can you go blind if you look at the sunrise and sunset? [duplicate]
Everyine knows its dangerous to look directly at the sun, but can you look safely at sunrises and sunsets without going blind? Because the uv radiaton and the light is much weaker. Or is it still very ...
