What is a constellation?

Warm-Up

A group of stars that form a pattern.

MYP Unit Question: What’s out there?

Area of Interaction: Human Ingenuity

Learner profile: Risk Taker

Standard: Explore current scientific views of the universe and how those views evolved.

Learning Target: Today I’m learning about celestial navigation because it will help me if I get lost.

Opening: “What’s visible in the night sky?”

Work Session: Notes “Navigation by the Stars”

Video – “Journey through Orion”

Closing: “Follow the Drinking Gourd”

What’s visible in the night sky?

Opening:

Navigating by the Stars

For thousands of years, individuals have relied on the stars.

Sailors – which direction to sail in

Shepherds – direction and entertainment (remember there was not electricity before 1940’s)

Farmers – when to plant and harvest their crops

Astronomers – observing the celestial skies

Writers – explained phenomena and entertainment

Slaves – travel to the free states and freedom

Why did they group the stars and give them names?

It was easier to find them in the sky

Enabled sailors and travelers to remember which hemisphere they were in.

What stars did they use?

When the Egyptians built the pyramids 5000 years ago, the north star was Thuban, in the constellation Draco the Dragon.

The “pole star” is the one that points due North year round in the northern hemisphere. (Sigma Octantis in Southern Hemisphere)

The Great Pyramid of Giza

Present day north star is Polaris, located in Ursa Minor (also known as Little Dipper).

Polaris (North star) is a circumpolar star (visible all year).

The stars appear to move because of Earth spinning on its axis.Polaris is always in the middle.

A photo of the night sky with the shutter left open. The stars appear to move in circular arcs.

The North Star is the star in the center.

The Importance of the North Star• The position of the North Star is fixed.• The angle of elevation of the North Star remains

constant throughout the night.• The North Star NEVER sets.• The position in the sky changes as you move

from the North Pole to the Equator. • It moves from being directly overhead to sinking

down to the horizon.

At the North Pole, the North Star is

directly overhead. At the equator, the North Star is at the

horizon.

How the North Star is Viewed from Earth

• The North Star’s position in the sky changes as you move from the North Pole to the Equator.

• It moves from being directly overhead to sinking down to the horizon.

Finding Your Latitude• If you measure the angle of elevation of the

North Star, you can determine your latitude on the map.

• Angle of Elevation = Latitude on the Map

The SextantThe sextant was a tool that mariners used to measure the angle of elevation of stars and the sun.

Will Polaris always be our North Star?

Yes, at least for the next 12,000 years or so and then . . .

Vega in the constellation of Lyra, the Harp,

will become our north star.

Why will it be the “new North Star?” Earth continues to “wobble” on its axis as it rotates around (24 hrs/day).

The Earth’s axis will take 26,000 years to “wobble” around a complete circle.

Vega is the fifth brightest star in the

summer sky.

The harp (lyre) was introduced by the Greek astronomer Ptolemy in the 2nd century.

The constellation is associated with the ancient Greek myth of Orpheus, the great musician killed by the Priestess Bacchantes. Orpheus carried with him the first lyre ever made, invented by Hermes and given to him by the god Apollo. After Orpheus' death, Zeus dispatched an eagle to fetch the lyre from the river into which it had fallen and then turned both into constellations in the sky.

How can we use constellations to “point out” other stars?

Know these three constellations: Big Dipper, Little Dipper, and Cassiopeia

Notice the rotational changes.

Use the Big Dipper (Plough or Big Bear) to locate the other constellations.

Ancient Greeks and Romans believed that a mythological king grabbed its tail, swung it around, and swung it into the sky to whirl around the North Pole forever. Some Native Americans believed that the three tail stars were hunters chasing the Bear.

Look for seven major stars: four in the "bowl" and three in the "handle." The two stars on the outside of the bowl are called the "pointer" stars. They point to Polaris, a bright star that is also called the North Star because with it you can figure out which way is north.

Orion, The Hunter

The three stars located in the handle of the Big Dipper are part of Orion’s belt.

Betelgeuse ("BEETLE-juice"), which is a giant red star, is located in the shoulder. The two brighter stars to the south are his legs.

Ancient people used Orion to predict the seasons: If it appeared at midnight, the grapes were ready to harvest. If it appeared in the morning, summer was beginning. If it appeared in the evening, winter had arrived.

Orion (Continued)

Betelgeuse

SiriusRigel

Rigel and Sirius both twinkle blue.Betelgeuse twinkles red.

Ancient Egyptians called Sirius "the Nile Star" because it always appeared in the sky right before summer began and the waters of the River Nile began to flood. In medieval Europe, people thought that a combination of light from the Sun and Sirius caused the hot and humid "dog days" of summer.

Use Two Sticks in a Field • On a cloudless night, drive a stick into the ground until

the tip of it is at your eye level. Behind it, plant a taller stick such that the tips of the sticks line up on a bright star, as you look at them. After a few minutes, the star will appear to have moved (but remember: stars don't move; it's Earth that's rotating). If the star seems to move . . .

• up, you are facing east.• down, you are facing west.• right, you are facing south.• left, you are facing north.

• http://www.topastronomer.com/StarCharts/Constellations/Lyra.php

• http://www.almanac.com/content/find-your-way-without-compass

• http://www.synapticsystems.com/sky/learnsky.html• http://www.badastronomy.com/bad/misc/badpole.html• http://www.space.com/15567-north-star-polaris.html