NAME ASTRONOMY 20 SECTION DAY/ S. V. LLOYD COMPUTER ACTIVITY 3: THE SEASONS: LENGTH OF THE DAY Overview Software Configuration The seasonal variation in temperature is due to two changes in the Sun's path over the course of the year: 1) the Sun's height (altitude) in the sky at noon 2) the number of hours the Sun is above the horizon The projects uses Stellarium version 0.10.6. See the "Stellarium" instruction sheet for setting up and using the program. Open the Sky and Viewing options window [F4]. On the Sky tab, in the Labels and Markers box, uncheck Stars. On the Markings tab, in the Celestial Sphere box, check Azimuthal grid. In the Constellations box, uncheck Show boundaries. On the Landscape tab, make sure you are using the Ocean landscape. Close the window. For this activity, we are going to be working in the Eastern time zone. To switch to Eastern time, go to the Configuration window and click on the Plugins tab. Click on Time Zone. Look at the bottom. If Load at Startup is not checked, check it and restart Stellarium. Otherwise, click on the configure button. In the Time Zone tab, Select Offset from UTC. Click the down arrow 20 times until the offset is -5:00 hours (this is Eastern Standard Time). Click on the Save settings button. On the Display formats tab, select 24-hour format. Quit Stellarium; then re-launch it. The Sun Set the time to 15:00:00 (this is 12:00:00 PST). Find the Sun in the south and select the Sun by clicking on it. Press the space bar to lock the Sun in position. Turn on the meridian if it isn't already (press the semicolon [;] key). The meridian is the green line that goes from the north point on the horizon thru the zenith to the south point on the horizon, dividing the sky into its eastern and western halves. The Sun is highest in the sky when it is on the meridian. This defines true noon. True noon isn't exactly 12:00 clock time. In the upper left you will find lots of info about the Sun. Some of these you will need for this project and others you can ignore. Magnitude and Absolute magnitude refer to the brightness of the Sun. You won't need these for this activity. RA/DE are right ascension and declination. These are the co-ordinates of the Sun on the celestial sphere, like longitude and latitude for places on the Earth. Skip these two lines for this activity. Hour Angle/DE. Hour Angle is how many hours and minutes it has been since the Sun last crossed the meridian. Declination is how many degrees north or south of the Celestial Equator a star is. When the Sun is on the Celestial Equator, its declination is 0 0' 0''
ASTRONOMY 20 LENGTH OF THE DAY P. 2 Sunrise & Sunset Az/Alt are azimuth and altitude. Azimuth is the direction of the Sun around the horizon. 0 = north 270 = west 90 = east 180 = south Altitude is how many degrees above the horizon the Sun is. 90 = at the zenith 0 = on the horizon Distance is in AUs (Astronomical Units), where 1 AU is the average distance between the Earth and the Sun: 150,000,000 km or 93,000,000 miles. This number will always be close to 1.0 AU. Apparent diameter is the angular size of the Sun in degrees, minutes, and seconds. It is always close to 30 minutes or half a degree. Make sure the Field of View (FOV) is about 60. It's displayed at the bottom center of the button bar. If the FOV is not between 40 and 80, zoom in or out until it is. Set the location to Toronto, Canada. Set the date to September 22. Set the time to 6:00:00 (6 a.m.). You should find yourself facing the eastern horizon. If not, find the Sun to lock on it [F3]. You should see the Sun about to rise in the east. If not, you haven't set the time zone correctly; go back and set it again. Run time forward until the Sun is precisely on the horizon. The altitude (Alt) will read 0. Record the time of sunrise and the azimuth (Az) of the Sun. Round off the time to the nearest minute. Round off the azimuth to the nearest degree. (If the number of minutes is more than 30, round up to the next degree.) True Noon is when the Sun crosses the meridian. Advance time until that happens. The Hour angle will be 0h 00m. Record the altitude and declination (DE) of the Sun and also the time. Round off the altitude and declination to the nearest degree. Round off the time to the nearest minute. Sunset is when the Sun is just on the horizon (altitude = 0 ). Record the time of sunset and the azimuth of the Sun. Round off the time to the nearest minute. Recall that in 24-hour time, 18:00 is 6:00 pm. Round off the azimuth to the nearest degree. Record your results in the table below. Repeat for Dec., Mar., & June. Set the location to Miami, United States. Repeat your measurements. Set the location to Quito, Ecuador. Repeat.
ASTRONOMY 20 LENGTH OF THE DAY P. 3 Toronto OF TRUE NOON DECLI- NATION NOON ALTITUDE Sept 22 6:10 90 12:11 0 46 18:10 270 Miami OF TRUE NOON DECLI- NATION NOON ALTITUDE Sept 22 6:14 90 12:13 0 64 18:14 270 Quito OF TRUE NOON DECLI- NATION NOON ALTITUDE Sept 22 6:07 90 12:07 0 90 18:06 270 Reset After you are done, go to the Configuration window and click on the Plugins tab. Click on Time Zone. Click on the configure button. In the Time Zone tab, Select Use system settings (default). Click on the Save settings button. Hit [Z] to turn off the grid and [B] to turn the constellation boundaries back on. In the Sky and Viewing options window, on the Sky tab, check Stars to turn on the star labels. Quit Stellarium.
ASTRONOMY 20 LENGTH OF THE DAY P. 4 Calculations Calculate the time above the horizon. The time above horizon is the set time minus the rise time. Report the result in hours and minutes. When subtracting the times, remember that there are 60 minutes in an hour, not 10. If you have to borrow an hour when subtracting, remember that you are borrowing 60, not 10. Example: sunrise time 7:45, sunset time 17:25. Since 45 is greater than 25, you have to borrow. Add 60 to 25 to make 85, then subtract: 1 7 6 : 2 8 5-7 : 4 5 9 : 4 0 ABOVE HORIZON QUITO ABOVE HORIZON MIAMI ABOVE HORIZON TORONTO Sept 22 12:00 12:00 11:59
ASTRONOMY 20 LENGTH OF THE DAY P. 5 Graph 2 Plot the azimuth of sunrise and sunset on each date for all three cities. Label with the city name and the date.
ASTRONOMY 20 LENGTH OF THE DAY P. 6 Analysis 1. How does the declination of the Sun vary over the course of the year? Does it depend on your location on Earth? 2. a) On what days of the year does the Sun rise due east and set due west? ("Due east" means exactly east--azimuth 90. "Due west" means exactly west--azimuth 270.) b) When does the Sun rise farthest north and set farthest north? c) When does the Sun rise farthest south and set farthest south? 3. a)on what day of the year was the Sun at the highest altitude at noon in Toronto? b)miami? c) Quito? 4. a) On what days of the year is the Sun above the horizon for about 12 hours wherever you are? b) In what city is the daytime about 12 hours long all year long? 5. Write a paragraph about how the length of the day (hours & minutes the Sun is above the horizon) depends on the time of year in the Northern Hemisphere. How does it differ in the Southern Hemisphere? 6. Write a paragraph about how the length of the day depends on how far north you are in the Northern Hemisphere. [13 March 2015]