Lab4_Motion_Sun

NAAP – Motions of the Sun 1/7 Name: Lab 4: Motions of the Sun – Worksheet Enter your answers to each question in the data tables and yellow highlighted areas below. When completed, please save and upload this file to the assignment submission link in Canvas. Seasonal Motion Work through the explanatory material on Sidereal vs. Synodic and Seasons and the Zodiac . All of the concepts that are covered in these pages are used in the Motions of the Sun Simulator. Question 1: For each of the following statements respond shorter, the same, or longer. (A) If the Earth revolved more rapidly, its sidereal day would be the same . (B) If the Earth revolved more rapidly, it solar day would be longer . (C) If the Earth rotated more rapidly, its sidereal day would be shorter . (D) If the Earth rotated more rapidly, it solar day would be shorter . Question 2: Use the Zodiac Explorer to answer the following questions. (A) On May 25 th , the sun is in the constellation of Taurus . (B) What would be a good time of year to observer the constellation Aries? The last few days of April and the first week and a half of May. (C) On July 4 th at midnight, the constellation Gemini is on the observer’s meridian. (D) At sunrise on Christmas Day, the constellation on the observer’s meridian is Sagittarius .

Paths of the Sun Simulator This simulator allows you to simulate the path of the sun for any date during the year for any latitude on the Earth. Spend some time familiarizing yourself with the simulator – most of the controls are fairly intuitive and similar to those in the preceding modules.  Practice using the yearly slider to move to different dates during the year.  Practice using the map to move to different latitudes during the year.  Note that the simulation lists the right ascension, declination, azimuth, and altitude for the sun at all times.  Note that some advanced features such as the sidereal time, hour angle, equation of time, and the analemma are available in a box in the lower left in this simulation, but will not be covered in this guide.  Note that there are three different animation modes. o If you select continuous , time will move forward in a natural fashion. You may adjust the rate at which time passes using the animation speed slider. You may modify this mode with the loop day check box which will cause the sun’s motion for the current day to continually repeat. o If you select step by day , time will leap forward in 24 hour increments and the time of day will not change.  Special care should be taken to make sure that you understand what is being simulated at all times. This is especially true in regard to discriminating between the yearly and daily motion of the sun. o Move to a middle United States Latitude like 35  N. Click show ecliptic and show month labels . This is the sun’s yearly path on the celestial sphere and is denoted by a white circle in the simulator. Note that it crosses the blue celestial equator on the equinoxes. o Change your time to noon (12 pm) and animate the simulator in the step by day mode. You can watch the changing meridinal altitude of the sun throughout the year. o Stop the simulation near the summer solstice. The simulator readout should state “The horizon diagram is shown for an observer at latitude 35  on 21 June at 12:00 (12:00 pm)”. Think about what the sun’s path should look like in the sky on that day. o Now check show the sun’s declination circle which is a yellow circle in the simulator. This is what the sun’s path in the sky would be on the summer solstice. Note that this circle has the proper meridinal altitude (78.8  ) and is a coaxial circle with the celestial equator (picture the slinky).

Date Meridional Altitude Rising Azimuth Setting Azimuth Summer Solstice 42.4 º N/A N/A Autumnal Equinox 19.0 º 90.0 º 270.0 º Winter Solstice -12.5 º N/A N/A Question 7: Note that the sun doesn’t rise every day from Nordkaap. How far would you need to move on the Earth to find a latitude where the sun does rise every day? You would have to move down to 66.5 ºN to get a fraction of sun rising during the day because if you subtract the tilt of the Earth (23.5 º) from 90 º you are left with 66.5 ºN. Anywhere North of 66.5 ºN or South of 66.5 ºS will not see the Sun rise on the Winter solstice. Question 8: The Paths of the Sun Simulator is also very useful for determining how long the sun is above the horizon each day. Simply make sure that the option for dragging the sun’s disk is set to time of day and drag the sun to the eastern/western horizon read the clock to determine the time at which the sun rises/sets. Latitude Date Rising Time Setting Time Total Time 0º June 21 6:00 18:00 12:00 Sept 21 5:50 17:55 12:05 Dec 21 6:00 18:00 12:00 41º June 21 4:35 19:35 15:00 Sept 21 5:50 17:50 12:00 Dec 21 7:30 16:30 9:00 66.5º June 21 0:20 23:45 23:25 Sept 21 5:50 17:55 12:05 Dec 21 11:40 12:15 0:35 90º June 21 Always risen Doesn’t set 24:00 Sept 21 Always risen Doesn’t set 24:00 Dec 21 Doesn’t rise Doesn’t set 0

Question 9: Based on your answers to the previous questions, is it best to refer to sunlight as a seasonal or daily phenomena? Does this depend on latitude? It is best to refer to sunlight as a seasonal phenomenon although it can be referred to in both ways. The general amount of sunlight doesn’t significantly change from day to day but from season to season there is a substantial change. However, it could also be recognized as a daily phenomenon because in certain places a day separates the Sun rising and not rising. Latitude greatly effects the amount of sunlight received because near the equator it is constantly around 12:00 year long while near the poles the Summer can bring 24 hours of sunlight while the Winter covers the Sun entirely.