All Questions
34 questions
4
votes
1
answer
362
views
Equation of Time (derivation Analemma)
In the document available here:
http://info.ifpan.edu.pl/firststep/aw-works/fsII/mul/mueller.pdf
I have been able so far to reproduce all missing details so far to the relation (33) of page 7:
$$\sin ...
- 233
1
vote
2
answers
87
views
Should I convert local time to UTC when computing the sun's position?
I'm trying to compute the sun's altitude and azimuth but should I convert the wanted local time to UTC by the time zone id? like in Saudi Arabia it uses AST (UTC +3 All the time) and Egypt uses EEST (...
- 133
11
votes
2
answers
2k
views
Always orient a sundial towards polar north?
I had a horizontal sundial made specially for my latitude (approx. 38° N). The default correct way to orient a sundial (in the northern hemisphere) is with the gnomon pointing towards polar north. The ...
- 221
20
votes
8
answers
11k
views
How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?
Google says the year is exactly 365.2422 days, and so they make a leap year every 4th year, but that ends up being 365.25 days per year on average. So every 100th year they don't have a leap year, but ...
- 451
1
vote
1
answer
127
views
How can I plot a rotary cam for the equation of time? [closed]
I'd like to use Solidworks to create a cam (peanut looking) for computing the equation of time in a pocket watch. Would appreciate any point to the right direction or advice.
Audemars Piguet EoT
1
vote
0
answers
133
views
Determining Time Based on Arc Seconds
So our arc day starts at 20°41'32 which is midnight (0:00) and ends 24 hours later at 21°42'42. According to my calculations it traveled 0 degrees, 59 minutes, and 30 seconds or 3570 arc seconds in 24 ...
- 177
16
votes
12
answers
6k
views
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 ...
- 169
2
votes
3
answers
7k
views
How were sundials and moondials possible 800 years ago?
In India, there is a temple named Konark Sun Temple which is around 750 years old and made up of 100% stones and rocks, and has a chariot which is headed by 7 horses and includes the Hindu god Surya(...
- 139
6
votes
1
answer
694
views
Is the speed of time much slower on sun surface?
The gravity forces on Earth and Sun is different and in Interstellar, they said something like high gravity slows time. So if we say Sun is N billion years old, that must be earth time but on Sun's ...
- 171
2
votes
0
answers
900
views
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 ...
- 121
2
votes
2
answers
291
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, ...
2
votes
0
answers
62
views
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 ...
- 1,017
6
votes
3
answers
2k
views
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 ...
2
votes
1
answer
84
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&...
- 1,017
0
votes
1
answer
710
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?
- 1
1
vote
2
answers
309
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 ...
- 1,559
1
vote
1
answer
650
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.
...
- 123
1
vote
2
answers
125
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 ...
- 13
1
vote
2
answers
80
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 ...
- 113
1
vote
0
answers
408
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 ...
- 11
3
votes
1
answer
197
views
How does the geometry for constructing a declining vertical sundial work?
I understand how to construct South-facing vertical an horizontal sundials and the geometry behind their construction by projecting an equatorial sundial into a plane, but I can't quite get how to do ...
- 133
1
vote
0
answers
56
views
What's the time in which the sun rises? [duplicate]
What's the time the sun takes in order to rise? (The time in which the solar disk crosses the horizon)
How does this time depend on local latitude and the sun's declination?
Assume that we're at sea ...
- 11
2
votes
2
answers
2k
views
Computation of mean sidereal time at Greenwich using solar position algorithm
Using Equation 28 in Section 3.8.1 of Solar Position Algorithm (Reda, I. and A. Andreas, Jan. 2008), I computed the mean sidereal time at Greenwich for 2003 October 17 for four different times (UT), ...
- 83
8
votes
1
answer
2k
views
Effect of the obliquity of the ecliptic / tilt of the Earth on the equation of time
In attempting to answer the question “why aren’t changes in sunset and sunrise times symmetrical around the solstices ?” I’ve got stuck on being able to explain the effect of the obliquity of the ...
- 83
4
votes
1
answer
1k
views
How do I adjust the sunrise equation to account for elevation?
I have been working with the sunrise and sunset formula, using the equations from Wikipedia. The problem is that, in my usage thereof, it seems that it only works for sea level; if I start with ...
- 141
0
votes
1
answer
646
views
At which winter hour is sun in zenith in DST?
When DST is introduced does it mean that the sun is in zenith one hour later (1pm winter local time) or one hour earlier (11am winter local time)?
Edit: The location is New York.
- 113
0
votes
2
answers
126
views
Can we, with arbitrary precision, calculate what's the place on earth that's closest to the sun on a given day?
Can we, with arbitrary precision, calculate what's the place on earth that's closest to the sun on a given date? If so, what's the math like? Say, if I wanted to calculate this within 1m, 10cm or 1cm ...
- 119
3
votes
2
answers
971
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 (+-...
- 133
1
vote
4
answers
996
views
Obtaining deltaT for use in software
I'm currently developing a javascript application in which I want to calculate the approximate position of the sun. This works quite fine but requires the value for deltaT (TT-UT) to be set depending ...
- 111
2
votes
8
answers
2k
views
What time and where on earth is the latest solar noon?
For context: I am visiting Portugal from Australia and after observing that people tend to start their days later, I realised that solar noon also seems to occur at a later time - about 1.20pm at the ...
- 29
2
votes
0
answers
677
views
How is the time of sunrise and sunset determined?
If I do a quick Google search for amsterdam sunrise, I immediately get the time back: 6:42 AM.
How is this time calculated?
(I ...
- 183
7
votes
3
answers
11k
views
How does the appearance of the analemma vary with latitude
How does the appearance of an analemma vary with latitude?
This what I take to be a definition of an analemma: If the position of the sun is plotted or photographed at noon clock time (say UTC) every ...
- 211
5
votes
1
answer
1k
views
How to calculate geocentric conjunction time and moon altitude at a given time
Umm al-Qura calendar of Saudi Arabia determine the new moon if these criteria meet at 29th day:
The geocentric conjunction occurs before sunset.
The moon sets after the sun.
I've got the formula to ...
- 151
8
votes
6
answers
39k
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 ...
- 217