Viewing Space from Earth
In the image below, we can see the horizon and hundreds of objects in the sky, including the Milky Way disk from bottom left to the top middle of the image. Just before we left school in mid March, we had completed a lesson on the observations that Ptolemy and Aristarchus (among many others) used to try and image our Solar System. In order to track planet movement, humans had to develop a way to map the position of celestial objects (stars, planets, moon, sun, comets, etc) in the sky. Just like we use latitude and longitude to plot a location on Earth's surface, we have two variables included in plotting a location on our sky. This lesson will introduce you to the system we use, and then give you practice in visualizing the system in whatever room you are in. Normally, I have an activity plotting objects on the walls and ceiling in my classroom, but we will have to improvise.
Pretend you are on the phone with a friend late at night and you are outside looking at the sky while talking. You spot an object in the sky but are not sure if it is a planet or star (they look nearly the same in the sky as viewed from Earth!!). You want to ask your friend to look at it too. How do you convey to them where in the sky it is? What information could you use to tell them where to look? This is the first step in learning how to plot and track celestial objects. By the end of this lesson, you will be able to go outside on a clear night, and find Venus among the beautiful vast sky using just two values.
1. Compass Direction
The first bit of information you can tell your friend is which compass direction to look in the sky. Now saying Southwest may not mean anything to your friend if they are not too good with directions, but thats what phones are for. Nearly all have built in technology that determines compass direction for you. On an iPhone, it is in the Utilities folder, usually with the calculator and measuring tool. Take your phone out and open the compass. Now think about the room you are in and which direction you are looking out the window. You should notice that the area in the sky where you observe sunrise is East, and where you observe sunset from your house is West. Now make the connection with a road near where you live. Clinton, Bullis, Rice, Jamison, 20A(Main St in EA) all are east-west roads. Transit, Pound, Bowen, Girdle, Townline, Two Rod, Four Rod and Three Rod are all north-south roads. Make that connection with whatever road I named is near where you live.
Ok, now we have to add a layer of detail to the directions. Just saying that a planet or star is in the southeast part of the sky does not narrow down the planet you are looking at. Look to the southeast on a clear night and you will likely see dozens or hundreds of specks that are planets or stars. We simply need to be more accurate, especially if you are trying to track subtle night to night changes in the position of an object like Ptolemy, Copernicus, Aristarchus, Brahe, or others. The diagram below solves that problem. We use the idea that 360 degrees are in a circle to give the directions a value. Except now rather than telling your friend to look Southwest which leaves some room for error, you can tell them to look at the bearing (direction) of 225 degrees, or 220 degrees, or even 223.7 degrees (imagine having a real powerful telescope where looking 223.7 or 223.6 degrees makes a difference in which star you are looking at)
So you do not have to submit these answers, but just mentally practice quickly. What is the compass degree value for:
- South Southwest?
- East Northeast?
Got the hang of it? So now if you wanted to get real nerdy with your friend, you could tell them look at a bearing (compass degree value) of 285 degrees to see the sunset tonight, and you would be right! And by the way, if any of you are considering the Navy, Army, Air Force, being an airline pilot, architect, land surveyor, civil engineer (roadway, bridge design) or commercial (big buildings) construction, this will be part of your daily life, so good to learn now.
2. Azimuth (angle above horizon)
The other bit of information needed is to tell your friend to look near the horizon, or way up in the sky almost straight above them, or halfway between. For this value, we also use degrees, and think of angles from Geometry class to help with this part. If the object were right on the horizon the value is 0 degrees, like the sun at sunset when the bottom half is sliced off from moving behind the Earth. Rarely do we see objects, especially stars or planets this low in the sky. Usually trees, buildings or other things are in the way. If you were laying on a blanket out in your yard and looked straight up, you would be staring at what we call the zenith point. Now stand up (figuratively) and point out one arm straight forward at the horizon. Put your other arm straight up pointing at the zenith. (I mean it, actually do this with your arms, it will help you understand!). Ok, now what angle do your arms make? If you are thinking a 90 degree angle, you are correct!!
Now, what if a planet is halfway between the horizon (0 degrees) and the zenith point (90 degrees)? Answer : 45 degrees.
In the image below, the person is pointing to a location in the sky about two thirds of the way up the sky, so about 60 degrees.
Ok, now you are ready to practice on your own. Please complete the Assignment, Celestial Sphere Practice in your assignments tab of MS Teams. Contact me with any questions!
Go to www.timeanddate.com and complete the activty in MS Teams on Sky viewing of the Planets from Buffalo. Take some time to play around with the information and animations provided and then answer all questions.