# sun_angle documentation

sun_angle gives the solar azimuth and elevation for any time at any location on Earth. This function was adapted from the SolarAzEl function by Darin C. Koblick.

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## Syntax

```[az,el] = sun_angle(t,lat,lon)
[az,el] = sun_angle(t,lat,lon,h)```

## Description

[az,el] = sun_angle(t,lat,lon) gives the solar azimuth and elevation in degrees at the specified geographic locations and times t in UTC. Input t can be datenum, datestr, or datetime format.

[az,el] = sun_angle(t,lat,lon,h) specifies height above sea level in meters. If no height is specified, elevations are automatically determined via the CDT function topo_interp.

## Example 1: Time series at one location

As I write this, I'm sitting at a coffee shop in Pasadena, California, (34.16N,118.13W). Determine the sun's azimuth and elevation right now and for the next 10 days.

```t = linspace(now,now+10,10000); % a time array 10 days long
t = t + 8/24; % converts Pacific Standard Time to UTC

[az,el] = sun_angle(t,34.16,-118.13);
```

Use subsubplot to plot the sun's angles:

```subsubplot(2,1,1)
plot(t,az)
axis tight
ylabel 'azimuth (deg)'
datetick('x','keeplimits')

subsubplot(2,1,2)
plot(t,el)
axis tight
ylabel 'elevation (deg)'
datetick('x','keeplimits')
``` ## Example 2: Global grid

Use cdtgrid to create a quarter-degree global grid and get the sun angles everywhere around the globe at the UTC strike of midnight on May 27, 2019:

```[lat,lon] = cdtgrid(1/4);

[az,el] = sun_angle('may 27, 1984 00:00:00',lat,lon);
```

Use imagescn to plot the solar azimuth and set the colormap to cmocean phase. Add political boundaries for context using borders.

```figure
imagescn(lon,lat,az)
cb = colorbar;
ylabel(cb,'solar azimuth (deg)')
caxis([0 360])
cmocean phase
borders('countries','color',rgb('gray'))
``` Overlay sun elevation as contours. Of course, the sun elevation is only physical where the sun is above 0 elevation, so only include positive contours:

```hold on
contour(lon,lat,el,[0 0],'k') % solid zero contour
contour(lon,lat,el,0:10:90,'k:')

text(0,0,{'It''s night time';'everywhere south';'of the solid contour'},...
'horiz','center')
``` ## Example 3: The tiny effects of elevation

The sun's angle is affected by elevation above sea level. By default, sun_angle uses topo_interp to determine ground surface elevation above sea level if no elevation is specified. But here we consider a hypothetical tower, 10,000 meters tall in the center of London (51.51N, 0.123W). What's the sun azimuth and elevation along this tower at 7:45 pm on July 14, 2019?

```t = 'july 14, 2019 7:45 pm';
lat = 51.51;
lon = -0.123;
z = 0:10000; % height along tower (m)

[az,el] = sun_angle(t,lat,lon,z);

figure
subplot(1,2,1)
plot(az-az(1),z) % plot relative to base
axis tight
xlabel '\Delta azimuth (deg)'
ylabel 'elevation (m)'

subplot(1,2,2)
plot(el-el(1),z) % plot relative to base
axis tight
xlabel '\Delta elevation (deg)'
``` Note the scientific notation on the x axis scales. That tells us the effect of elevation is miniscule on the scale of a few thousand meters.

## Author Info

This function was originally written by Darin C. Koblick using the formulas described here: http://stjarnhimlen.se/comp/tutorial.html#5. It was adapted for the Climate Data Toolbox for Matlab in 2019 by Chad A. Greene.