The length of the day

I. Purpose:
Learn how the elliptical orbit of the earth around the sun influences the times of sunrise and sunset.

Activity:
Open tables of sunrise/sunset for entire year. Using part A, open the file for Sunrise and Sunset in Washington, DC for the current year.
From this table determine the following dates:
    The date of the earliest sunrise:
    The date of the latest sunset:
    Are these the same day? Why do you think that they might not be?

    The date of the earliest sunset:
    The date of the latest sunrise:
    Are these dates the same as that of the winter solstice? Why might they differ?

From the table, answer the following questions:
     What day is the longest?
    What day is the shortest?
    On what date is the sun above the horizon for exactly twelve hours?
    Is this on the date of the spring or autumnal equinox? Why or why not?
After you have thought about these questions, see discussion for more information.

II. Purpose:
Learn how sunrise and sunset times change with geographical position

Activity:
Using part A, determine the time of sunrise and sunset on January 1, April 1, July 1, and October 1 for the U.S. Cities: Washington, DC (latitude 39 deg. North; longitude 77 deg. west) and Fairbanks Alaska ( north latitude 65 deg.; longitude 148 deg. west)   Write down these times in the following tables:

From the data in the tables, answer the following questions:

        In which city does the time of sunrise vary the most during the year?
        In which city does it vary the least?
    Why do you think this might be?

        Now that you see how the times of sunrise and sunset change with latitude, estimate the times of sunrise and sunset on each of the four days for:
    Seattle, WA (latitude 47.5 deg. north; longitude 122.3 deg. west) and
    Miami, FL (latitude 26 deg. north; longitude 80 deg. west).
Write your estimates in the following tables:

Now find the time of sunrise and sunset on these dates for Columbus, OH (latitude 40 deg. north; longitude 83 deg. west). The latitude of Columbus is almost the same as that of Washington.
    Are the times of sunrise and sunset the same?
    Why or why not?

Now that you understand how sunset and and sunset change with latitude, how do you think that the length of twilight will change with latitude? Check your understanding by looking up the beginning and end of astronomical twilight in Fairbanks, Washington, DC, and Quito. Use the tables for the times of twilight. (Astronomical twilight begins in the morning when the sun rises to 18 degrees below the horizon and ends in the evening when the sun declines to 18 degrees below the horizon. At that time the sky is nearly as dark as it will get during the night.)  You may find it helpful to write the times in the following tables:

III. Purpose:

Learn a little about the moon