ASTRONOMY

The Earth, Moon, and Sun CHAPTER 1

SECTION 1 – EARTH IN SPACE

I. HOW THE EARTH MOVES The earth moves in 2 ways: A. Rotation 1. rotation - the spinning of earth on its axis 2. axis – the imaginary line running through the earth from the North to South poles 3. one full rotation creates one day on Earth

B. Revolution 1. the movement of one object around another 2. the earth revolves around the Sun 3. the path the Earth follows is called its orbit a. the orbit of earth is ellipse (oval) in shape 4. one full revolution creates one year

C. Calendars 1. calendar – system of organizing time 2. Egyptians then Romans developed early calendars 3. current calendar – days with a leap year every 4 years a. Year – One Earth Revolution (around the sun) b. Month – One Moon Revolution (around the Earth) c. Day – One Earth Rotation (on its axis)

II. THE SEASONS ON EARTH A. How Sunlight Hits Earth 1. sunlight hits earth directly near the equator and at an angle near the poles a. direct light warms more than light at an angle B. Earth’s Tilted Axis 1. The earth has seasons because its axis is tilted 23.5 degrees 2. The part of earth tiled toward the sun experiences summer because it has longer days and more energy (heat)

C. Earth in June 1. The North Pole is more tilted toward the sun a. The Northern Hemisphere experiences summer because of more direct sunlight b. The Southern Hemisphere experiences winter because the sunlight is spread over a larger area (not as strong) D. Earth in December 1. opposite from June

E. Solstices 1. the day the sun is the greatest distance from the equator (due to the earth’s tilt) a. Summer solstice – the sun is farthest north of the equator (longest day of light for Northern Hemisphere) 1. around June 21 b. Winter Solstice – the sun is farthest south of the equator (longest day of darkness in the Northern Hemisphere) 1. around December 21 F. Equinoxes 1. equinox – “equal night” – then the day and night are the same length 2. around March 21 and Sept 22

SECTION 3 – PHASES, ECLIPSES, AND TIDES

I. MOTIONS OF THE MOON The moon moves through space like the Earth, both rotating and revolving The changing positions of the moon, earth, and sun cause phases of the moon, eclipses, and tides

II. PHASES OF THE MOON The moon DOES NOT make it own light The moon REFLECTS the light from the sun Phases – shapes that you see of the moon o Moon phases repeat each time it Revolves around the Earth o Crescent – less than half of the moon is seen o Gibbous – more than half of the moon is seen o Waxing – getting larger o Waning – getting smaller

III. ECLIPSES When an object comes in between the sum and another object and makes a shadow Why don’t eclipses happen every month? – the orbit of the moon is slightly (4°) from earth’s orbit A. When Do Solar Eclipses Occur? 1. when the moon passes directly between the earth and the sun B. Total Solar Eclipse 1. umbra – the darkest part of moon’s shadow a. Cone shaped, coming to a very small point on earth 2. only people in the umbra see a full solar eclipse C. Partial Solar Eclipse 1. penumbra – the lighter part of the moon’s shadow 2. part of the Sun appears covered by the moon. a. The sun is bright on the edges so it is not safe to look at the partial eclipse

D. When Do Lunar Eclipses Occur? 1. lunar eclipse – when the earth is between the moon and the sun 2. the earth blocks the sun, casting a shadow on the moon E. Total Lunar Eclipse 1. earth, like the moon, has an umbra and penumbra 2. Total lunar eclipses can be seen from anywhere on earth that the moon can (at night) F. Partial Lunar Eclipse 1. most eclipses are partial

III. TIDES A. The Tide Cycle 1. tides – the rise and fall of the earth’s oceans a. Every 12.5 hours 2. high tide - the force of the moon’s gravity pulls on the water on earth, creating a bulge on the side of earth near the moon and on the opposite side 3. the other 2 sides of the earth experience low tide B. Spring Tide 1. the sun also pulls on Earth’s waters 2. extra high high tides because the sun and moon are pulling in the same direction C. Neap Tides 1. the Sun, Earth, and Moon create a 90° angle, pulling in opposite directions, resulting in less difference between high and low tide

Section 5 Comets, Asteroids, and Meteors CHAPTER 3

I. COMETS Comet – loose collection of ice, dust and small rocky particles whose orbits are usually long, narrow ellipses A. 1. coma – fuzzy outer layer of a comet caused by the sun melting the ice particles 2. nucleus – the solid center of a comet B. 1. gas tail and dust tail, caused by proximity to the sun 2. tails point away from the sun C. 1. Kuiper Belt – area past Neptune containing comets 2. Oort cloud - region of comets far beyond Pluto

II. ASTEROIDS Asteroids - Small rocky objects too small to be considered planets Most revolve around the sun between Mars and Jupiter Asteroids can have elliptical orbits and can collide with other asteroids or planets

III. METEORS Meteoroid - a chunk of dust or rock in space Meteor – a streak of light caused by a meteoroid Meteorite – a meteoroid that have hit Earth’s surface Meteors can be seen every night, sometimes in mass called meteor showers

Section 1 Telescopes CHAPTER 4

I. ELECTROMAGNETIC RADIATION Telescope – Electromagnetic Radiation – A. Forms of Radiation 1. B. 1. wavelength – 2. visible light spectrum - 3. electromagnetic spectrum -

II. TYPES OF TELESCOPES Telescopes – instruments that collect and focus light and other forms of electromagnetic radiation Optical telescope – a telescope that uses lenses or mirrors to collect and focus visible light A. 1. use convex lenses to gather and focus light 2. convex lens – B. Reflecting Telescope 1. uses a curved mirror to collect and focus light 2. first built and used by Isaac Newton in 1668 C. 1. D. Other Telescopes 1.

III. Observatories – Many large observatories are located on mountain tops or in space A.Advanced Telescopes 1. B.Telescopes in Space 1.

Section 2 Characteristics of Stars CHAPTER 4

I. CLASSIFYING STARS Stars are classified by their color, temperature, size, composition, and brightness A.Color and Temperature B.Size C.Chemical Composition 1. 2.

II. THE BRIGHTNESS OF STARS Brightness depends on both size and temperature A. 1. apparent brightness – brightness as seen from earth 2. closer things appear brighter, so this doesn’t measure the actual brightness of a star B. 1. absolute brightness – the brightness a star would have if it were a standard distance from earth 2. use apparent brightness and distance to calculate

III. MEASURING DISTANCE TO STARS A B C

IV. THE HERTZSPRUNG-RUSSEL DIAGRAM