# Tag Info

Accepted

### Why is the sun not directly overhead at noon on the March equinox at N 0° 0' 0.00" E 0° 0' 0.00"?

It never is exactly, directly overhead on the vernal equinox at the Greenwich meridian. You know that it happens on different days in different years so it must be happening at different times on ...
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### Why is the sun not directly overhead at noon on the March equinox at N 0° 0' 0.00" E 0° 0' 0.00"?

In addition to the March 2021 equinox occurring 2.4 hours before 12:00 UTC as stretch explains, you found a maximum altitude at 12:07:25 UTC because apparent solar time was 7.4 minutes behind mean ...
• 16.5k

### Why is the sun not directly overhead at noon on the March equinox at N 0° 0' 0.00" E 0° 0' 0.00"?

The time of the equinox, and the Sun being over the 0° meridian are determined by different motions: The Earth spins around its axis. The Sun crosses over the 0° meridian once every solar day, when ...
• 309
Accepted

### Why doesn't the solar azimuth vary uniformly

The Sun's hour angle, measured around the celestial equator, changes at a nearly constant rate. The gnomon of a sundial is aligned with the polar axis to take advantage of this. The celestial equator ...
• 16.5k

### How to calculate the maximum and minimum solar azimuth at a given location?

Thanks to Ralf Kleberhoff for Pointing me in the right direction. Step 1: Find Summer Solstice Date For the accuracy needs of this question simply finding the hemisphere and picking the most common ...
• 203

### an exercise from Spherical Astronomy by Smart

Constant for every star with different declination's. Though you would have to assume the the declination is such that it can have an azimuth of 90 each, not all stars will. Depending on your ...
• 1,173

### Azimuth angle and elevation angle of a heliostat mirror

As I said in my comment, you appear to be using an Azimuth system different from what most astronomy programs will return it in. As long as you're consistent, it won't matter, but double check to ...
• 1,139

### Why does the sun rise north of east between the vernal and autumnal equinox?

You know, the first time someone told me this, I was absolutely certain they were confused, ignorant, or otherwise mistaken, and I told him he had his facts wrong. To be precise, we were talking about ...
• 634
Accepted

### relation between azimuth angle of the sun and angle of the shodow

Your diagram is correct, your maths isn't. The bearing of the object's shadow is, as your diagram shows, away from the sun. If the bearing of the shadow is 75°, then the sun must have an azimuth of ...
• 88.7k

### Obtaining deltaT for use in software

The actual equations used by NASA are located here: https://eclipse.gsfc.nasa.gov/SEcat5/deltatpoly.html I failed to find any pre-written code and consequently wrote my own in Swift. The equations ...
• 91
Accepted

### How to calculate the maximum and minimum solar azimuth at a given location?

The azimuth angle from due south to the point where an object rises or sets is a function of the latitude (lat) and declination (decl), as follows: cos(angle) = -sin(decl)/cos(lat) This ignores ...
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### Error when calculating Alt/Az from Ra/Dec

The algorithm on that page is very simplistic and is probably the source of a good portion of that error. It's best to test your code using a very accurate ephemeris, even if your final goal is to ...
• 1,139

### Path of sun calculation using java

The NOAA formula sheet expresses some quantities in radians, some in degrees, and some in minutes of time. It does say which is which, but it's easy to miss. A few minor code changes can help expose ...
• 16.5k
1 vote

### How to calculate the local time of sunrise and azimuth of rising point of Sirius?

This is from: https://www.celestialprogramming.com/risesetalgorithm.html . It has a Javascript implementation and example you can run for the rise, set, and transit times. Keep in mind that if you ...
• 1,139
1 vote
Accepted

• 7,085
1 vote
Accepted

### Determine sun azimuth and elevation for shading a window throughout the year

You can use a package such as the pyephem package for python. It can calculate the position of any astronomical object. However for the sun since it moves along the ecliptic, roughly at a uniform ...
• 88.7k
1 vote
Accepted

### Calculating azimuth from equatorial coordinates

lat2 = 0 and lmst = 0 place the vernal equinox at the zenith, so most points on the ecliptic should have azimuth either ...
• 16.5k
1 vote

### Finding a location using the direction of shadow, UT and date approximately

Planetarium software, such as Stellarium, or astronomical computation software such as pyephem can compute the exact position of the sun at any date, time and location. It is then simple trigonometry ...
• 88.7k

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