Linked Questions

12
votes
3answers
7k 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 ...
10
votes
2answers
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 ...
1
vote
1answer
958 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 ...
2
votes
1answer
694 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 ...
3
votes
2answers
102 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 ...
2
votes
3answers
197 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). ...
1
vote
1answer
212 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 ...
0
votes
2answers
109 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 ...
0
votes
2answers
106 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 ...
0
votes
1answer
91 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 ...
3
votes
1answer
84 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 ...
0
votes
0answers
107 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 ...