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22 votes

Does the sun's rising/setting angle change every few months?

The Sun rises and sets at a different point on the horizon every day. The change is small, so without careful observations, it may take several days or weeks to be fully aware of the change. ...
JohnHoltz's user avatar
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18 votes

Does the sun's rising/setting angle change every few months?

You're not silly1, it certainly swings back and forth (North and South) one full cycle every year. It's directly related to why days are longer in the summer and shorter in the winter. I am no expert, ...
uhoh's user avatar
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15 votes
Accepted

Why isn't Spring equinox on 1st of April?

The calendar is designed so the 21st of March is set to the spring Equinox, and everything else is calculated from there. So the reason that the equinox doesn't occur on the first of April is boring. ...
James K's user avatar
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14 votes
Accepted

Realistic description of a sunrise viewed from the asteroid belt?

Light pollution is mostly caused by diffusion from the atmosphere—humidity and dust within it. This is not to say that there is no light pollution at all elsewhere, as rock reflects light and can ...
Pierre Paquette's user avatar
13 votes
Accepted

Straightforward derivation of the sunrise equation

We can start by converting between equatorial coordinates (right ascension $\alpha$ and declination $\delta$) to horizontal coordinates (azimuth $\text{Az}$ and elevation/altitude $a$). If you want to ...
HDE 226868's user avatar
  • 36k
12 votes

Does the sun's rising/setting angle change every few months?

This answer is a supplement to the existing answers. I looked around for nice graphs showing the sunrise azimuth over the year for various latitudes, but I couldn't find anything suitable. So I just ...
PM 2Ring's user avatar
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11 votes
Accepted

Daylight Time Expansion

This phenomenon is the equation of time, the annually varying difference between apparent solar time (what a sundial indicates) and mean solar time (related to civil time). It has two components: The ...
Mike G's user avatar
  • 18.2k
8 votes

Why does sun rise further north of where it does any other time of year? I know rises differently depending on the season but this is like never seen

Nothing did change except the keenness of your observation. That Sun and Moon rise exactly in the East and set in the West is only true on two days in the year, at equinoxes in Spring and Fall. The ...
planetmaker's user avatar
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8 votes
Accepted

Mean Sunrise Time

The author is doing the following: $\log_{10} \tan(14^o 26') = -0.58943$ and then adding 10 to get to 9.41057. I didn't know about that practice, but it's akin to shifting the decimal point. Anyway, ...
Glorfindel's user avatar
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7 votes
Accepted

Was the Earth-Sun distance ever calculated based on the time difference between night and day?

You have a good idea. You mentioned 4 effects already (clock accuracy, latitude, time of year, and clear horizon), but there is another effect that is larger than those: atmospheric refraction. ...
JohnHoltz's user avatar
  • 7,797
7 votes

Does the sun's rising/setting angle change every few months?

The Sun does indeed drift across the sky throughout the year, not only rising higher in the summer and lower in the winter, but also varying along an east-west axis. This can be shown by observing the ...
Nuclear Hoagie's user avatar
5 votes

Angle the Sun makes with the horizon during sunset

Short answers: It's not just angular velocity of Earth's rotation times elapsed time. You do need to factor in declination and latitude. Using your representative date and observer location: The ...
stretch's user avatar
  • 1,608
5 votes

Angle the Sun makes with the horizon during sunset

The transformation from the equatorial coordinates to altitude (azimuth is not important) is given by $$\sin{a}=\cos{h}\cos{\delta}\cos{\phi}+\sin{\delta}\sin{\phi}$$ Let's say that $t=0\rm\, s$ at ...
User123's user avatar
  • 2,879
5 votes
Accepted

Predicting accurate time of local sunrise in mountainous area?

The PeakFinder app1 can do most of what you're looking for. It's available for Android and IOS as well as through a web browser. The app shows the paths across the sky for both the sun and moon2 and ...
Alex Hajnal's user avatar
  • 1,189
5 votes

Can stars really be seen after sunrise from Mount Everest?

The reason that you can't see stars in the daytime is that the atmosphere scatters sunlight and effectively blots them out. But even where I live, a dark sky area, the brightest stars are visible ...
Chenmunka's user avatar
  • 208
4 votes

Sunrise and sunset times when compared between the vernal and autumnal equinoxes

Instead of looking at sunset/sunrise times, it's easier to look at noon, which is right in the middle between sunset and sunrise: 11:50am in March and 11:35am in September. The fact that noon doesn't ...
Glorfindel's user avatar
  • 4,780
4 votes

How to find the first Julian day with the same Earth-Sun constellation

Most formulas accept a Julian Day as input, but internally usually use the number of days (or years, or centuries) since Jan 1, 2000 12:00pm. Take the function below, which accepts JD as input, but ...
Greg Miller's user avatar
  • 5,562
4 votes
Accepted

Where can I download the historic sunrise and sunset times for a location?

You might want to find an astronomical almanach or year book. They usually have tables of sunrise and sunset times. They usually cover only one year, though and accurate times only for selected places....
planetmaker's user avatar
  • 17.6k
4 votes
Accepted

Sidereal time of rising and setting of the sun on the arctic circle

You need to intepret the question a bit. By "June 22" they probably mean "Summer Solstice", likewise for "Dec 22". At the solstice the right ascension of the sun is 6hr/...
James K's user avatar
  • 116k
3 votes
Accepted

Is the appearance of the twilight not constant in the interval before the sunrise?

The length of Astronomical twilight isn't constant, but the main reason is the tilt of the Earth, and not the orbital speed of the Earth. The change from day to night is a result of the Earth spinning....
James K's user avatar
  • 116k
3 votes
Accepted

Does the Time of Sunset (Sunrise) Change Over Time Given a Fixed Location and Consistent Atmospheric Conditions?

Shalom! Strictly speaking, yes, the time of sunset does change, but the amount of change is imperceptible to humans over a lifetime. The change is due to the slowly varying obliquity of the Earth on ...
Pierre Paquette's user avatar
3 votes

Does the sun's rising/setting angle change every few months?

I hope someone can come along and make this more precise, but I'm pretty sure the effect is greater the further you move away from the equator. So it would be more noticeable in Canberra (35° S) than ...
JonathanZ's user avatar
  • 131
3 votes

How long for the sun to traverse its diameter at the pole?

The Sun's daily motion does not affect its altitude on the poles, because it revolves around the zenith (and the zenith coincides with the celestial pole). This means the Sun's altitude is only ...
Tosic's user avatar
  • 1,681
3 votes
Accepted

Sunrise - from earth - sun position or when sun rays reaches earth?

It's when we see the Sun's rays and includes refraction. It also is the moment we see the first glimpse of the sun. Think of it this way: we humans need to know sunrise and sunset for our human ...
BillDOe's user avatar
  • 1,371
3 votes

Difference in Sunrise times between Horizons and NOAA

(Figured it out) The Horizons system is showing the times in UT, whereas NOAA is showing in local time. Also, Elevation of 180 degrees is not sunrise. Additionally, that first column is Apparent ...
Pradyumna's user avatar
  • 171
3 votes

Meaning of $\cos H$ in the rising and setting formula

The problem is not with the spherical triangle. A triangle can always be formed between three points on a sphere as long as the three points are not on a great circle. (The three points are the ...
JohnHoltz's user avatar
  • 7,797
3 votes

New moon rise same spot on horizon as sunrise, almost same time

At exact new moon, moon and sun can be separated by at most 5 degrees, as the lunar orbit around earth is tilted a bit (5 degrees) against the earth's orbit around the sun (what we call the ecliptic). ...
Ralf Kleberhoff's user avatar
3 votes
Accepted

math tool to compute time of sunrise and sunset

The rise and set equations below are from Astronomical Algorithms, and the approximate Sun position is from the Astronomical Almanac. The rise/set algorithm works for any celestial object given it's ...
Greg Miller's user avatar
  • 5,562
3 votes

What is the chance that the Sun will not rise tomorrow?

My guess is that the most likely mechanism would be something like a world-war/pandemic that temporarily prevents astronomers from analyzing sky surveys and/or prevents planetary defense strategies ...
Thomas's user avatar
  • 161
3 votes

Why is moonrise/moonset before sunrise/sunset on some days but after on others?

While one sunrise to the next is about 24 hours, one moonrise to the next is about 24 hours and 50 minutes. The extra 50 minutes are due to the Moon's orbit about the Earth. It therefore shouldn't be ...
David Hammen's user avatar
  • 33.5k

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