• Special care should be taken to make sure that you understand what is being simulated at all times. This is especially true in regard to discriminating between the yearly and daily motion of the sun.
- Move to a middle United States Latitude like 35°N. Click show ecliptic and show month labels. This is the sun’s yearly path on the celestial sphere and is denoted by a white circle in the simulator. Note that it crosses the blue celestial equator on the equinoxes.
- Change your time to noon (12 pm) and animate the simulator in the step by day mode. You can watch the changing meridinal altitude of the sun throughout the year.
- Stop the simulation near the summer solstice. The simulator readout should state “The horizon diagram is shown for an observer at latitude 35° on 21 June at 12:00 (12:00 pm)”. Think about what the sun’s path should look like in the sky on that day.
- Now check show the sun’s declination circle which is a yellow circle in the simulator. This is what the sun’s path in the sky would be on the summer solstice. Note that this circle has the proper meridinal altitude (78.8°) and is a coaxial circle with the celestial equator (picture the slinky).