Unit 1 : Activity 1 : Talking About Things in the Sky : "Which Way is North?" : What's Up? : Unit Exam

Unit 1: How to Point to a Star
Unit 2: Where on Earth Are You?
Unit 3: Earth's Rotation and the Sun's Apparent Motion
Unit 4: Yearly Changes in the Sky
Unit 5: Seasons and Climate
Unit 6: Sundials
Unit 7: Navigation
Unit 8: Ancient Astronomy
Unit 9: Constellations




"Which Way is North?"

---------"I say head North," Jim said quietly. He dug the toe of his boot into the leaves and looked at the others. He wasn't sure if he should speak up like that or just set his backpack down and let his big brother, Steve, and Steve's bigger friend, Roy, argue it out. They had left the trail three hours earlier to go "trailblazing" as Roy called it, but after a while they couldn't find their way back. That's when Steve and Roy started arguing.

---------Both older boys paused in their yelling and looked over at Jim. Jim felt like he wanted to be sucked into his backpack and disappear. We wanted to be back at the camp with water boiling for some food. He was hungry.

---------"Now why would you say that?" Steve spat on the mat of leaves. Steve had started spitting since he got in high school this year.

---------"Well I remember looking on the map back at camp and there's a road that runs North of here, goin' East and West. If we walked North we should run into the road."

---------Roy looked back at Steve and said, "That's not a half bad idea, Steve." He spat on the ground to match Steve. "I say we go for it. What do you think?"

---------"Sounds better than what we've been doing. Yeah, let's go," Steve answered.

---------"Which way is North?"

---------"I dunno. Don't you?"

 

CompassAs part of getting oriented, you may need to find out which way is north. There are a variety of methods to find north. In North America, and particularly in the Midwest, many streets are laid out north-south; so if you look at a map you should be able to get a good idea quickly of which direction is north.

If you can recognize the "Big Dipper" in the constellation of Ursa Major, you can use this to find the star nearest the North Celestial Pole, Polaris, otherwise known as the North Star. But remember, this method will only give you a rough idea of where North is. It will not be accurate enough for sundials or telescope stands.

If you can find the Big Dipper, trace a line from the scope end of the dipper - as shown to the right - and you will intersect the North Star. Remember that the North Star is not very bright.

The North Star is so important because it does not appear to move in the night sky. Therefore we can navigate by it.

Since all the stars appear to rotate around the North Star, that means that the Big Dipper also rotates around the North Star. That is why, depending on where you are on the Northern Hemisphere and the time of night, the Big Dipper might be under the horizon. In Ames, Iowa, for example, the constellation is circumpolar, but from Hawaii it is not. Circumpolar means that the constellation is visible in the sky year round.

Another way of finding North is to mark the shadow of a post on the ground. Remember that the Sun rises from the East, so the mark on the ground will be to the West. In the evening, as the Sun sets, mark the shadow of the same post. Since the Sun sets in the West, the shadow you marked will be generally to the East. If you run a line from the base of the pole outward, between the two shadow marks, that will be North as long as the shadows are the same length. The animated graphic to the right will help you understand. Click the play button to activate it.

 


Still don't know how to find the Big Dipper and North Star?
Click Brisban's photo on the left for
NO FRILLS HELP.

What can a Photo Tell Us?

Star Trails PhotoA camera aimed at either pole and left to make a time exposure will produce a photo of "star trails" like the one to the right. This really makes it obvious that there is a special direction (or 2 points in the sky) around which all the rest of the sky appears to rotate. Those points are located directly above the North and South Poles of Earth. The apparent motion of the sky around these points comes from the Earth's rotation on its axis. In Unit 3 you'll explore more consequences of Earth's rotation.

In the Southern Hemisphere there is no "South Star" to signal the position of the pole. A picture like this one that is taken in the Northern Hemisphere usually shows a small, intense arc very close to the North Celestial Pole that is the bright star Polaris, the North Star, from which this course takes its name.

Many more images like this one can be found at http://www.aao.gov.au/images.html.

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