Lab 3



Lab 3: SeasonsNAMEAfter you complete this lab you should be able to describe the seasons of the year, explain why Earth experiences seasons, and why the temperatures vary with a regular pattern during a year.?When we do this lab in the classroom, we use globes and spotlights to study the seasons and the angle of sunlight at different times of year, so if you have a globe and flashlight handy, try using them as supplements while you use Stellarium to complete the lab. If a link does not work, copy and paste it into a new browser window, or try a search engine such as Google, Bing, or Yahoo to find the answers. "The link did not work" is not acceptable. A. The Noon-time altitude of the Sun in Champaign-Urbana:By now you should know from the lessons and text that there are four days each year that mark the change in seasons. In the northern hemisphere, the vernal equinox occurs in March, the summer solstice in June, the autumnal equinox in September and the winter solstice in December. All these occur between the 20th and 23rd of the month, and can vary by a day or two each year.?To see why and how the seasons change, begin by opening Stellarium.Set the following conditions:?Time: 13:00:00 (the "noon" position of the Sun during Daylight Saving Time)Date: Current year, March 20 - the vernal equinoxViewing Location: Champaign, ILGaze Direction: South?Turn off the atmosphere ("A"), turn on the equatorial grid ("E"), select the Sun and center it in your field of view. As you use Stellarium, you may find this list of shortcuts useful: ascension (RA) and declination (Dec) are coordinates in the sky which also measure east and west or north and south for RA and Dec respectively. Unlike azimuth and altitude, which make their measurements relative to the horizon, RA and Dec are measured relative to points in the sky. They can be used by any observer on Earth - they are not dependent on the observer’s time or location. Declination and right ascension can be seen as analogous to the Earth coordinates of latitude and longitude.A declination of 0° is on a line called the Celestial Equator (like Earth's equator). The declination increases to 90° toward the North Celestial Pole and decreases to -90° approaching the South Celestial Pole.The right ascension is measured relative to a point in the constellation Pisces and is expressed in hours rather than degrees. Since it takes 24 hours for the stars to make a trip around the sky, RA ranges from 0 to 24 hours.Stellarium also shows the coordinates of the stars on the date currently displayed as RA/Dec (of date) e.g. J2018.4 for 2018-05-24. It can also show what the coordinates were in 2000 as RA/Dec (J2000). The numbers are slightly different because of precession.Rounding and degrees: Some coordinates are measured in degrees (°), arcminutes ('), and arcseconds ("). For example, you may see a declination of 19°35'12". Round them to the nearest degree by checking the arcminute value. If it is 30' or more, round up. In our example, it rounds up to 20°.The right ascension is listed in hours (h), minutes (m), and seconds (s). For example, you may see a RA of 7h20m39s. Round them to the nearest minute by checking the second value. If it is 30s or more, round up. In our example, it rounds up to 7h21m.Most answers for this lab can be found in the lessons on the seasons, your pre-lab, and in the textbook reading.?1. Record the RA/Dec (of date) for the Sun. Round your answers to the closest hour (hr) of RA & degree (°) of declination. As you should now see, the origin (zero point) of the RA/Dec coordinate system is based on the Sun’s position on this date, the vernal equinox.??2.?The coordinate line is not named on Stellarium, but you should be able to figure it out from the lessons and reading assignments in the text on seasons. What is the name of the 0 degree, east-west Celestial Sphere coordinate line where the Sun is found on this date? 3. Scroll around to see where the coordinate line from question 2 meets the horizon. What two places (cardinal direction – N,S,E,W) does this coordinate line intersect the horizon? Be specific.4. Refer back to the information for the Sun and record the altitude (“Alt”) of the Sun. Round your answer to the nearest degree. Since the Sun is on the Celestial Equator on the equinoxes, the noontime altitude of the Sun is the same as the altitude of the Celestial Equator on those two days. The altitude of the Celestial Equator can be determined for any location by subtracting the latitude of the location from the altitude of the zenith of 90°. ?Make sure the Sun is still centered. Open the Date and Time window and click the up arrow in the month column to advance time one month at a time. Keep going until you’ve advanced one full year and watch the Sun's position change relative to the coordinate lines. Watch the “Alt” coordinate in the information, and see how the Sun’s altitude changes each month.5. How does the position of the Sun change relative to the Celestial Equator through one full year?Please download and install the NAAP labs from the University of Nebraska website. the NAAP labs software, click on “Basic Coordinates and Seasons”, then click to open the “Seasons and Ecliptic Simulator”.In the upper right corner there is a red line that indicates the observer's latitude. Move this up to get as close as you can to the latitude of Champaign of 40? North. In the window on the left, you can tilt the orbit so you can watch as Earth revolves around the Sun from several different angles. Make sure the selection "celestial sphere" is highlighted just below this window. The white path the Sun is on is the ecliptic, and the green line is the Celestial Equator. In the window on the lower right you can see how the angle of sunlight changes during the year. Make sure the selection "sunlight angle" is checked to see this. Move the red bar in the month line to March 20 and start the animation. Watch how the position of the Sun changes through one full year.Set the date to June 21. (If you are using Stellarium to check this answer, make sure your time is set to 13:00)6. What is the noontime altitude of the Sun on this date for observers at Champaign’s latitude of 40° N? 7. Subtract the altitude of the Sun on the equinox (your answer to question 4 above) from the noontime altitude of the Sun on the summer solstice (your answer to question 6). What is the angle between the Sun and the Celestial Equator on the summer solstice?Change the date to September 22, the autumnal equinox.8. What is the noontime altitude of the Sun on the autumnal equinox?Change the date to December 21, the winter solstice.?9. What is the noontime altitude of the Sun on the winter solstice? 10. Subtract the altitude of the Sun on the winter solstice (your answer to question 9) from the altitude of the Sun on the autumnal equinox (your answer to question 8). What is the difference between the altitude of the Sun on the winter solstice and the autumnal equinox? B. Other Latitudes:In the first part, we focused on the view from central Illinois, but the view is different for different latitudes. ?Return to Stellarium and set the following conditions:?Time:?13:00:00 (noon position of the Sun for Daylight Saving Time)Date: June 21Viewing Location: North Pole - you need to set this manually (step-by-step instructions below)Latitude: 90° N (the longitude doesn't matter)?To set the latitude to the North Pole, open the Location window. In the Latitude box change the Latitude to 90° 0’ 0". Do NOT hit "enter". Type "North Pole" into the Name/City box and then click the "Add to list" box in the lower right. The red arrow showing your location should disappear, but if you look closely, you can barely see the tip of it at the top of the map. Close the Location window. Make sure the ground is showing "G" and the atmosphere is off "A", so you can see the information. Center the Sun in your field of view and click Control + "=" to advance one solar hour at a time and go through a full twenty-four hours.?Note the directions on the horizon as you go through the day.11. Where does the Sun set at the North Pole on June 21? What is the altitude (apparent) of the Sun at noon (13:00:00) on this date? What is the altitude (apparent) of the Sun at midnight (01:00:00)?on this date?From the lab so far, you should realize that the Sun never gets very far above the horizon when you're at the North Pole, and when you're near Champaign, the Sun never gets as high as the zenith. As you move farther to the South, the Sun gets higher and higher in the sky until you reach a point where it does reach the zenith at least one day of the year.12. What is the latitude (on the Earth), in degrees, where the Sun reaches the zenith (altitude 90°) at noon on June 21? (Hint: think again about the angle of Earth’s tilt). You can also use the Seasons and Ecliptic Simulator again and turn on the labels in the window on the upper right to help. Check the pre-lab as well.13. What is the name of this latitude?14. What is the latitude, in degrees, where the Sun reaches the zenith (altitude 90°) at noon on December 21? ?15. What is the name of this latitude?Change your location in Stellarium to 66°30' N latitude and keep the same longitude as Illinois (W ~88°). Set the time to 13:00:00 and the date to June 20. Center the Sun and step time forward one hour at a time Ctrl + "=" until 01:00:00 (midnight during Daylight Savings Time).16. Where is the Sun at midnight, with regard to the horizon (direction and altitude)?What is the name of this latitude? (Refer to the labels in the simulator or check the pre-lab if you aren't sure).C. Altitude of the Sun and the Seasons:Return to the Seasons and Ecliptic Simulator in the NAAP labs.Just below the window on the left make sure "orbit view" is selected and what you see is an animation (not to scale) of Earth revolving around the Sun with the axis pointing toward Polaris, which is way off to the upper left. In the upper window on the right, make sure the latitude is as close as you can get it to 40° N. In the lower window on the right, check the selection for "sunbeam spread" to see a patch of sunlight. Start the animation and watch through one full cycle to see how the size of this patch of sunlight changes.17. Describe the relationship between the angle of the Sun above the horizon and the patch of sunlight.18. How does the angle of sunlight affect the temperature on the ground? (Think about what you've read in the lessons and the text).D. Length of Day:Now let's see if the length of the daylight has an effect on the temperature. You can check the sunrise and set times on the Time and Date website here: You must copy and paste this link. The year doesn't really matter, so use the current one and change the month to June, the date to 21, and the location to Champaign, IL. If using the Time and Date website, you will need to scroll down the page and change the Month and Year to June 2020 (although the link should take your directly there). 19. What time is sunrise? What time is sunset? Approximately how many hours of daylight are there on this date?Change the date to December 21.Here is the link for Time and Date - . What time is sunrise? What time is sunset? Approximately how many hours of daylight are there on this date?21. Based on your answers to 19 and 20, how does the length of daylight affect the temperature?E. Earth and Sun:Review the Seasons and Ecliptic Simulator again and watch the image on the left as Earth revolves around the Sun. It would also help to read the Seasons lessons.22. What two things cause the height of the Sun to change during the year?23. What is the relationship between seasons in the northern and southern hemisphere? ................
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