Paths of the sun as demonstrated by the Planetarium star projector
For Students Preparing for the Regents Earth Science Exam
To arrange a visit for your school group, please call (585) 697-1942 at least three weeks in advance.
Celestial Sphere, a live lecture-demonstration in the Planetarium Star Theater, aims to help students prepare for the Regents Earth Science exam. The hemispherical dome of the Theater serves as an accurate model of the celestial sphere. Observe and predict the apparent daily paths of the sun and stars in the Planetarium sky. Measure the height of the midday sun in units of degrees, using the Planetarium's meridian. Note how the sun's paths change as a function of season and latitude (inferring, generalizing, identifying variables). Observe the apparent motion of stars around Polaris, the North Star, due to Earth's rotation. Observe the order and sequence of the phases of the moon. Watch computer animations illustrating the how the tilt of Earth's axis causes seasons.
Click here to download a typical script (76k pdf)
NYS Learning Standards: ELA1; MST3(2,4,5); 4PS(1,6)
Outline of the Program
(The exact order of presentation may vary, but these main points will be covered.)
1. The Celestial Sphere
The Star Theater dome is a model of the sky. The dome corresponds to the visible portion of the celestial sphere. The base of the dome (known to architects as the springline) represents the horizon. The highest point at the center of the dome represents the zenith. Markers along the horizon indicate the cardinal points in the compass directions north, south, east and west.
2. Apparent motion of the stars due to Earth's rotation
Earth's rotation every 23 hours 56 minutes causes stars (and other celestial objects such as the sun) to rise and set in our sky. Halfway between rising and setting, a star crosses our meridian, the imaginary line in the sky extending through our zenith from due north to due south. When a star crosses the meridian it reaches its highest altitude (measured in degrees of angle above the southern horizon).
We use the Planetarium star projector to put Earth's rotation into "fast forward." We watch the night sky as it appears from the latitudes of the continental U.S. We notice the following:
If a star rises far south of east:
If a star rises due east:
If a star rises far north of east:
If a star is always above the horizon, never setting:
3. Apparent changes due to Earth's revolution around the Sun; seasons
In the Planetarium, we can see what the sky would look like if we could see both the sun and the other stars in the daytime. With this view, we see that the sun appears against different background stars in our sky at different times of year, because of Earth's revolution around the sun. Over the course of a year, the sun traces out a path, called the ecliptic, that goes all the way around the celestial sphere.
Half of the ecliptic is north of the celestial equator, half south of it. The places where the ecliptic intersects the celestial equator are the equinoxes. The ecliptic and celestial equator intersect at an angle of 23.5 degrees. The places where the ecliptic is farthest north and south of the celestial equator are the solstices.
Each day of the year, the sun occupies a different position along the ecliptic. Therefore, each day of the year, the sun follows a different path through our sky:
At the time of the December solstice:
At the time of the March or September equinox:
At the time of the June solstice:
These changes in the Sun's path change the duration and angle of insolation we receive in each season.
The seasons are caused by the 23.5-degree tilt of Earth's axis. Seasons are NOT caused by changes in the distance between Earth and Sun.
4. The sky as seen from different latitudes
So far, we have seen the sky only as it appears from the latitude of Rochester, NY, about 43 degrees north. Now we look at the paths of stars and the sun as seen from other latitudes.
We examine the sky and its motions as seen from latitudes of 90 degrees north (at the North Pole), zero degrees (on Earth's equator) and somewhere south of Earth's equator. When we travel south of our home latitude we discover stars that never rise above Rochester's horizon.
The altitude of Polaris, the North Star, is approximately equal to the observer's latitude. Navigators at sea could measure their latitude relatively easily (as long as they were in Earth's northern hemisphere) by simply measuring the altitude of the North Star. As seen from Rochester, the altitude of the North Star is about 43 degrees.
Finally we view an actual video of Earth rotating in space, taken by the Galileo spacecraft. By analyzing the way sunlight strikes our planet we figure out what time of year the video was taken.
5. Other topics
If time permits, we will review the retrograde loop of Mars that occurs in the real sky in January 2010.
Links to further information outside the RMSC web site:
Animation of Earth's Seasons
This short video, created at Strasenburgh Planetarium, posted on YouTube, uses carefully planned words and images to show how Earth's seasons are caused by the tilt of Earth's axis.
Animation of the Moon's Phases
Another short Strasenburgh-created video, posted on YouTube, shows the cycle of the moon's phases from an outer-space point of view, then from the Earth's point of view.
U.S. Naval Observatory Astronomical Applications Department
Go here for lots of information about sunrise and sunset times, phases of the moon, eclipses, calendars, frequently asked questions and much more. http://aa.usno.navy.mil
Virtual Reality Moon Phases
Do you need to track the phases of the moon? If the sky is cloudy, or if you're in a hurry, you can get an accurate picture of the moon's phase for any date from January 1, 1800 through December 31, 2199 from the U.S. Naval Observatory's Virtual Reality Moon Phase web page. Note: when you enter a time, you'll need to use 24-hour (military) time. That is, 4pm will be 16 hours; 8pm will be 20 hours, and so on.
US Naval Observatory Time Service Department
Look at the Naval Observatory Master Clock, the final authority on time in the United States. http://tycho.usno.navy.mil
Fred Espenak's Eclipse Page
Provided by a NASA scientist, the best source for detailed information about the timing and visibility of eclipses, solar and lunar, past, present and future. http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html
NASA's Astronomy Picture of the Day
This is a wonderful resource. Links and searching capabilities make it possible to learn a little or a lot about almost any topic in astronomy or space exploration: http://antwrp.gsfc.nasa.gov/apod
One way to understand the apparent motion of the sun in the sky is to watch shadows on the ground. This free 3-D modeling software allows you to create a virtual building, then add shadows accurately corresponding to a date, time and location. You can join several renderings to make a movie showing the shadow's progress during the day. See Google's online user's guide for more information: