Theodolite

Theodolite is an award-winning app for Apple iOS that has many applications for my sky watching activities. Wait, what is a "theodolite?"

A surveyor's instrument for measuring horizontal and usually also vertical angles. Source credit: Merriam-Webster (dictionary).

Tracking cloud motion

I used the "Theodolite" app to determine the position of the four cardinal points for my location. That enables me to know the direction clouds are moving across the sky.

15 JUN 2026 | Facing north.

15 JUN 2026 | Facing east.

15 JUN 2026 | Facing south.

OK, I was a little off-center for the direction "south."

15 JUN 2026 | Facing west.

Tracking weather satellites

Radio signals from polar orbiting weather satellites can be received using free software and relatively inexpensive hardware including an RTL-SDR and V-dipole antenna. For best results the V-dipole antenna should be oriented north-south, with the open end of the "V" facing south. For more information, see the following article: Simple NOAA/Meteor Weather Satellite Antenna: A 137 MHz V-Dipole.

Oh by the way, of course I used the "Theodolite" app to determine the direction of north and south relative to the position of my portable rig for reception of weather satellite radio signals.

Tracking daily- and annual cycles in the Sun's apparent path across the sky

The June Solstice will occur at 8:25 UTC on 21 June 2026 (4:25 a.m. EDT), according to the Earth's Seasons - Equinoxes, Solstices, Perihelion, and Aphelion page, Astronomical Applications Department, U.S. Naval Observatory.

The Motions of the Sun Simulator can be used to explore the apparent motion of the Sun across the sky on the June Solstice. The following screenshot shows the simulator configured for 21 June at 12 noon. Be sure to set the "animation mode" for "continuous" and "loop day," as shown in the following graphic.

"Motions of the Sun Simulator" set for 21 JUN at 38.8 N latitude.

Notice the Sun rises along the northeastern horizon and sets along the northwestern horizon. At Washington, D.C. (38.89° North latitude and 77.03° degrees West longitude) the Sun reaches a maximum altitude of 74.7° above the horizon, the highest maximum altitude all year. "This maximum angle occurs precisely at local solar noon, which usually happens around 1:00 PM EDT due to the Earth's axial tilt of 23.5° and daylight saving time adjustments." Source Credit: Google AI.

Also notice the odd-looking figure eight that is shown in red on the preceding screenshot. It's called an analemma. The crest of the figure eight shows the Sun's maximum northern latitude on the June Solstice.

Many years ago I used the "Theodolite" app to show the direction of sunrise on the March Equinox. You might want to do something similar for either sunrise or sunset on the June Solstice.

20 MAR 2011 | 7:12 a.m. | Facing east.

Tech Tips

The "Theodolite" app isn't available for devices running the Android OS. According to Google AI, the top-rated comparable app is "Sololocator - GPS Field Camera" ($0.99), available from Google Play.

Related Resources

• Theodolite Augmented Reality Navigation Viewfinder for iPhone and iPad
• Theodolite / Theodolite HD User Manual
• Earth's Seasons - Equinoxes, Solstices, Perihelion, and Aphelion - Astronomical Applications Department, U.S. Naval Observatory
• Motions of the Sun Simulator
• Equinox sunrise - walter sanford's photoblog
• Position of the Sun on the horizon at sunrise - University of Nebraska-Lincoln
• Sunrise Positions in Washington, D.C. - a post from my old Web server, rescued from the Wayback Machine Internet Archive, featuring a time series of photos by Dr. Robert Weinbeck, American Meteorological Society

Copyright © 2026 by Walter Sanford. All rights reserved.