Learning Goal: I’m working on a other discussion question and need the explanation and answer to help me learn.
Astronomy class
Attention, Navigators, this is your Captain speaking,
It’s time to do something with your sextants. We are calling the inclinometer a sextant, now. The building of the sextant was worth ten points. Using it to measure the changing elevation of the Sun will also be worth ten points. The elevation of the Sun is the angle between the horizon and the Sun.
You will make observations of the Sun over a period of four hours, between 10 a.m and 2 pm. The Sun will reach its peak high in the sky at around (but not exactly) 12 pm. That time we call Local Noon. The objective of this project is to determine what time local noon occurs where you live.
Roughly point the ruler or straight edge at the Sun, just as you would aim the barrel of a gun. Do not stare at the Sun; use the Sun’s shadow. Orient the ruler or stick so that the size of its shadow is minimized, that is, made as small as it can be. If the ruler is parallel to the ground (not pointing at the Sun), the shadow will be big. The closer the ruler is to pointing at the Sun, the smaller the ruler’s shadow will be. When it is pointed exactly at the Sun, the ruler’s shadow will appear as a very short line. The weighted string will hang against one of the degree markings on the protractor. Press the string against the protractor as soon as you have minimized the ruler’s shadow. If you do not hold the string in place after you have minimized the shadow, the string will move, and you will wind up reading the wrong number. There are several photos in the module, showing the slowly shrinking ruler shadow as the ruler is pointing closer and closer to the Sun. Sorry about the crappy focus in some of the pix.
Record the degree number under the string. If the degree number is less than 90, subtract the degree number from 90. For example, if you recorded 70, 90 – 70 equals 20 degrees. Record the 20 degrees. That angle is the elevation angle of the Sun. If the degree number under the string is greater than 90, subtract 90 from the degree number. For example, if you recorded 120, 120 – 90 equals 30. Record the 30 degrees. That angle is the elevation of the Sun. If you are simply writing down numbers that you see under the string and nothing more, YOU ARE DOING IT WRONG. Those numbers are not the Sun’s elevation. You must find the difference between the number under the string and 90, as explained above. THAT is the Sun’s elevation. So, take an elevation measurement at about 10 a.m., then every half hour after that for four hours. Eight elevations. You should see the elevation numbers rising, reaching a max, then decreasing again. The numbers won’t change much between 11:30 a.m. and 1:30 pm. The time of that max is the time of local noon.
There is a video in this module that discusses how to aim and read the protractor, but ignore the part about aiming it by looking at the Sun. I do not want you to look at the Sun. Use the shadow method. The video does discuss how to read the protractor, so you might want to watch the video for that part. A new video is in the works but will not be ready this semester.
Submit a table of Time, Degrees, and Elevation.
You must have credit for your inclinometer/sextant (Project 1) to be eligible for points on this project.
This is your Captain speaking. Good Luck.
