UNIT 4

SPACE EXPLORATION

Chapter 10 – The Universe• Text page 350

ASTRONOMY – branch of physics which studies celestial bodies and the universe

Any natural object out in space

Section 10.1 : Observing the Stars

page 352

• STAR – celestial body of hot gas with a nuclear core and makes it’s own thermal energy

Star configurations seen from earth were often interpreted as different forms called constellations.

Constellations page 354

• IAU (International Astronomical Union) lists 88 constellations

Although stars appear close together they are actually very far apart

5 Common Must Know Constellations

– Use your star chart to find them!

1. Ursa Major – The Greater Bear

• Contains the asterism the big dipper

Smaller groups of stars within constellations

2. Ursa Minor –The Lesser Bear

3. Cassiopeia – The Queen

4. Orion – The Hunter

5. Leo – The Lion

• Find the Constellations!

Magnitude page 356

• How Bright a Star appears depends upon:1. How bright the star is

2. How far away the star is

• Brighter stars with greater magnitudes are represented as larger dots on a star map

• Sirius (m=-1.46) is the brightest star in the night sky (other than our sun)

Movement of the Stars page 359

• The big dipper’s end stars are called pointer stars as they line up with Polaris- the North Star.

Page 355

Polaris appears stationary in the Northern Hemisphere as it lies above the North Pole and the stars appear to rotate clockwise (EAST – WEST)around it

Animation

Circumpolar Constellations those that NEVER go below the horizon and as a result can be seen all year!

Examples include: Ursa Minor, Cassiopeia,

Ursa Major

Motion of the Sun, Moon, and Planets page 359

• We can only see constellations when the sun goes down... And we can only see constellations in the opposite direction of the sun at any particular time of the year!

• The path the sun travels through the sky is called the ECLIPTIC. The 12 signs of the zodiac are on this ecliptic

12 Signs of the Zodiac

Student Ecliptic Demo!

Section 10.2 : Early Models of the Universe page 352

ARISTOTLE383-322 B.C.E

• geocentric universe with Earth at the center and the sun, moon and planets revolving around it

• reasoning based on the fact that the same pattern of stars could always be seen

Geocentric Model

PTOLEMY83-168 B.C.E.

• realized that for Mars, the retrograde motion was not explained

an apparent switch in the motion of a celestial body from East to West or vice versa as viewed from Earth

• new model with each planet attached to a sphere with its center at earth but revolving around an epicycle (a point on its orbit) as it travelled around Earth

• used an astrolabe

COPERNICUS1473-1543

• Heliocentric view (with the sun the center of the universe)

• Earth rotate about its axis daily

Heliocentric Model

GALILEO1564 - 1642

• first to use a refracting telescope (had a magnification of 20x, less than most modern backyard telescopes)

• noticed phases of Venus which supported the heliocentric model

Refracting Telescope• First used by

Galileo to study space

• Uses lenses to focus an image

KEPLER1571-1630

• enlisted the help of Tycho Brahe and discovered planets actually orbited the sun in elliptical orbits

KEPLER’S LAWS

1. All planets move in Ellipses, with the sun at one focus

2. Planet sweep out equal area in equal time therefore they do not orbit at a constant speed

3. The time of a planets revolution is directly proportional to its distance from the sun

NEWTON1643-1727

• predicted that gravity explains why the planets stay in orbit, the LARGER the size the greater the force of gravity, smaller objects revolve around LARGER

• use Newtonian laws to determine how to send satellites in orbit,

• Invented a reflecting telescope

Reflecting Telescope

• Create and used by Newton

• Uses mirrors to focus an image