Linked Questions

11 votes
4 answers
10k views

Why is twilight longer in summer than winter and shortest at the equinox

I recently decided to set my alarm clock to wake me up when it is "dark" out. In the end, I decided to set my clock to the earliest time that nautical sunrise is in my state (Illinois) and stick with ...
firebush's user avatar
  • 231
13 votes
2 answers
2k views

Cancelling out earth rotation speed, Altazimuth mount

I have a Dobsonian telescope. It is using Altazimuth mount. Basic idea of using it is to target the object by moving telescope vertical axis perpendicular to the ground, and an elevation axis that is ...
Kocur4d's user avatar
  • 233
1 vote
1 answer
2k views

Determining sunrise and sunset times based on azimuth and elevation

If I observe the sun and measure the local azimuth and elevation, and I also have my latitude, can I calculate the local sunrise and local sunset times? If so, how would I calculate it? Further, can ...
jlaverde's user avatar
  • 113
2 votes
1 answer
1k views

Finding hour angle, altitude

I know the latitude and longitude of a city ($41^\circ 87'$ N, $87^\circ 62'$ W), the declination and right ascension of a star($16.51^\circ$, $68.98^\circ$) and the local time, date (27.12.2017, 1:20 ...
Alex S's user avatar
  • 51
3 votes
2 answers
232 views

Is there any formulae to calculate whether the sun will depress 18 degrees or more below the horizon on a certain day / location?

I'm trying to code a piece of software which will calculate some times for me that would greatly help me in my day to day but none of my formulae work if the sun doesn't go at least 18 degrees below ...
15150776's user avatar
1 vote
1 answer
785 views

How can we estimate if a certain astronomical object will be visible from a place on earth?

If we have the RA/DEC of an object that we want to observe, how can we tell if that object is visible from our place on earth (at a particular time of the year)? Given that the part of the sky we are ...
jm22b's user avatar
  • 147
2 votes
3 answers
374 views

Position of specific stars in the sky as a function of time

I'm a beginner in astronomy and I'm trying to figure out how to model the positions of stars in the night sky mathematically (ie a function which spits out azimuth and altitude as a function of time). ...
John Smith's user avatar
0 votes
0 answers
266 views

Calculating angle between the sun and a perpendicular to earth given lon/lat & time

If you had your longitude/latitude, and the time/date, how could I go about working out the angle between your normal and the sun? At first I was doing a simplistic approach of assuming elliptical ...
BinkyNichols's user avatar
0 votes
2 answers
144 views

Can someone explain me this diagram from an article?

How should I understand this 59 degree mentioned below, what does it mean? I could not get it. The photo is a diagram from an article dedicated to the invention of the ecliptic. The photo is from my ...
Kiril Mladenov's user avatar
0 votes
2 answers
159 views

Distance from W(West) to vernal equinox

I am pretty new to astronomy and the project I am currently working on requires some knowledge of equatorial coordinate system. As long as I have been researching this question, I understood that ...
Sardor Gulyamov's user avatar
0 votes
1 answer
154 views

ra for sun vs stars

There is formula for stars sideral time: $$ra - \arccos(-\tan(dec)*\tan(lat)).$$ where $ra$ - is right of ascension at the vernal equinox. $lat$ = latitude $dec$ = declination Is it applicable ...
user3026756's user avatar
3 votes
1 answer
113 views

Deducing the hour based on RA

I'm making a technological project. The goal is to write a program that gets an image of the nightsky and predicts the hour in which the photo was taken. I implemented a well-known method using the ...
omri slovatik's user avatar
2 votes
0 answers
86 views

Daytime length and sunrise / set cardinal directions

Let me illustrate the question with an example. On Feb 2nd 2022, the sun rises in Los Angeles at cardinal direction 110 and sets in direction 250 (according to timedate website). This means that the ...
Rob's user avatar
  • 21