The Perfect Sunset

Recently, I showed a student of mine a Flash applet from the Astronomy Department at the University of Nebraska-Lincoln. It very generally demonstrates how the sunset changes its North-South location on the horizon during the course of the year (due largely to the tilt in the Earth's axis).

In talking about the sunset's movement, my student expressed to me a lifelong desire: to see the sun setting over the Golden Gate Bridge. It takes a little figuring out, since not only does the sunset move during the year but where it happens depends on where on Earth you are (eg If you are far North of the Equator during the summer, then sunset will appear to happen much farther North than if you were standing at the Equator)!

After thinking about different locations in the East Bay to view the Golden Gate Bridge from, I've determined that Cesar Chavez Park is the optimal place (or possibly the nearby Berkeley Pier).


Latitude is a measure of how far North or South a place on the Earth is from the Equator, so knowing the latitudes of both Cesar Chavez Park and the Golden Gate Bridge will help us to find the date of our particular sunset. Latitude is given in degrees, like the way you measured angles in Geometry.

The Flash applet below gives you control over the Time of Day, Date, and Latitude of the observer. Given that

Latitude of Chavez Park: 37.87^oN
Latitude of Golden Gate Bridge: 37.82^oN

can you use the Flash applet below to find the date of the perfect sunset?

[There are some hints below the applet that may help you.]



Key (for 3-D Observation Simulator)

• Yellow Line: Sun's Declination (Daily Path)
• White Line: Sun's Ecliptic (Annual Path)
• Blue Line (E-W): Celestial Equator
• Blue Line (N-S): Prime Hour Circle

Hint 1

If you're feeling stuck, play around with the Date and Latitude. See what happens in different places at different times of year. What patterns can you find?

Hint 2

Pay close attention to the Sun's Declination. Go ahead and read about it on Wikipedia. There's a continuous measure of declination in the box in the lower left of the applet.

Hint 3

The latitudes of Cesar Chavez Park and the Golden Gate Bridge are just 0.05^o apart. How significant is that in our calculations, considering that our accuracy is limited by that of the applet?

[Cross-posted at Roland's Miscellany.]