1. Chapters 18-21
Space

2. Astronomy: The Original Science
Astronomy, the study of the universe, is one of the oldest sciences.
The units of the modern calendar- days, months, and years- are based on observations of objects in space.
Ptolemaic theory states that the Earth is at the center of the universe.

3. Astronomy: The Original Science
Coperican theory that’s the sun is at the center of the universe.
Modern astronomy has shown that there are billions of galaxies.

5. Telescopes
Man first used his eyes to study space, but then developed telescopes to help him see more.
Refracting telescopes use lenses to gather and focus light.
Reflecting telescopes use mirrors to gather and focus light.

6. Telescopes
The atmosphere blocks most forms of electromagnetic radiation from reaching to Earth.
To overcome this limitation, astronomers place telescopes in space.
Astronomers study all wavelengths of the electromagnetic spectrum including radio waves, microwaves, infrared light, visible light, ultraviolet light, x-rays, and gamma rays.

7. Formation of the Universe
Observations show that the universe is expanding.
The big bang theory states that the universe began with an explosion about 13.7 billion years ago.
Cosmic background radiation helps support the big bang theory.

8. Formation of the Universe
Scientists use different ways to calculate the age of the universe.
Scientists think that the universe may expand forever.

9. A Solar System Is Born
The solar system formed out of a vast cloud of dust and gas called a nebula.
Gravity and pressure were balanced until something upset the balance.
Then the nebula began to collapse.

10. A Solar System Is Born
Collapse of the solar nebula caused heating at the center, while planetesimals formed in surrounding space.
The central mass of the nebula became the sun.
Planets formed from the surrounding materials.

12. The Sun: Our Very Own Star
The sun is a large ball of gas made mostly of hydrogen and helium.
The sun consists of many layers.
The sun’s energy comes from nuclear fusion that takes place in the center of the sun.

13. The Sun: Our Very Own Star
The visible surface of the sun, or the photosphere, is very active.
Sunspots and solar flares are the result of the sun’s magnetic fields that reach space.
Sunspot activity may affect Earth’s climate, and solar flares can interact with Earth’s atmosphere.

14. The Earth Takes Shape
The effects of gravity and heat created the shape and structure of Earth.
The Earth is divided into 3 main layers based on composition:
The crust
The mantle
The core

15. The Earth Takes Shape
The presence of life dramatically changed Earth’s atmosphere by adding free oxygen.
Earth’s oceans formed shortly after the Earth did, when it cooled off enough for rain to fall.
Continents formed when lighter materials gathered on the surface and rose above sea level.

16. Planetary Motion Rotation is the spinning of a planet on its axis.
Revolution is one complete trip along an orbit.
Planets move in an ellipse around the sun.
The closer they are to the sun, the faster they move.

18. Planetary Motion
The period of a planet’s revolution depends on the planet’s semimajor axis.
Gravitational attraction decreases as distance increases and as mass decreases.

19. The Nine Planets
In the order in which they orbit the sun, the nine planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
2 ways in which scientists measure distances in space are to use:
Astronomical units
Light years

21. The Nine Planets
The inner planets are spaced more closely together, are smaller, and are rockier than the outer planets.

22. The Inner Planets
A period of rotation is the length of time that an object takes to rotate once on its axis.
A period of revolution is the length of time that an object takes to revolve around the sun.

23. The Inner Planets Mercury is the planet closest to the sun.
Of all the terrestrial planets, Venus has the densest atmosphere.
Earth is the only planet known to support life.
Mars has a rich volcanic history and shows evidence of once having had water.

24. The Outer Planets Jupiter is the largest planet in our solar system.
Energy from the interior of Jupiter is constantly transferred to its exterior.
Saturn is the second largest planet.
It is still forming as a planet.

25. The Outer Planets
Uranus’s axis of rotation is titled by almost 90 degrees.
Neptune has a faint ring.
Neptune’s atmosphere contains belts of clouds.
Pluto is the smallest planet.
It’s moon, Charon, is more than ½ its size.

27. Planetary Satellites: Moons
Mars has 2 moons: Phobos and Deimos.
Jupiter has dozens of moons.
Ganymede, Io, Callisto, and Europa are the largest.
Saturn has dozens of moons.
Titan is the largest.
Uranus has several moons.

28. Planetary Satellites: Moons
Neptune has several moons.
Trition is the largest.
Pluto has its moon, Charon, which is more than ½ its size.
Our Moon is called Luna
Scientists reason that the moon formed from the debris that was created after a large body collided with Earth.

29. Phases and Eclipses
As the moon revolved around Earth, the amount of sunlight on the side of the moon changes.
Because the amount of sunlight on the side of the moon changes, the moon’s appearance from Earth changes.
A solar eclipse happens when the shadow of the moon falls on Earth.
A lunar eclipse happens when the shadow of Earth falls on the moon.

30. Small Bodies of the Solar System
Studying comets, asteroids, and meteoroids can help scientists understand more about the formation of the solar system.
Asteroids are small bodies that orbit the sun.
Meteoroids are similar to but smaller than asteroids.

31. Small Bodies of the Solar System
Most meteoroids come from asteroids.
Most objects that collide with Earth burn up in the atmosphere.
Large impacts, however, may cause a global catastrophe.

32. Mapping Stars Astronomers use constellations to organize the sky.
Altitude, or the angle between an object and the horizon, can be used to describe the location of an object in the sky.
The celestial sphere is an imaginary sphere that surrounds the Earth.

33. Mapping Stars
Using the celestial sphere, astronomers can accurately describe the location of an object without reference to an observer.
A light-year is the distance that light travels in a year.
The Doppler effect causes the light emitted by objects that are moving away from an observer to appear to shift toward the red end of the spectrum.

34. Mapping Stars
Objects moving toward an observer are shifted toward the blue end of the spectrum.
Observations of redshift and bluseshift indicate that the universe is expanding.

36. Stars The color of a star depends on its temperature.
Hot stars are BLUE.
Cool stars are RED.
The spectrum of a star shows the composition of a star.

37. Stars Scientists classify stars by temperature and brightness.
Apparent magnitude is the brightness of a star seen from Earth.
Absolute magnitude is the measured brightness of a star at a distance of 32.6 light-years.

38. Stars
Astronomers use parallax and trigonometry to measure distances from Earth to stars.
Stars appear to move because Earth’s rotation.
However, the actual motion of stars is very hard to see because stars are SO distant.

39. The Life Cycle of Stars
New stars form from the material of old stars that have gone through their lives.
Types of stars include: main-sequence stars, giants and supergiants, and white dwarf stars.
The H-R diagram shows the brightness of a star in relation to the temperature of a star.
It also shows the life cycles of stars.

40. The Life Cycle of Stars Massive stars become supernovas.
Their cores can change into neutron stars or black holes.

42. Galaxies
Edwin Hubble classifies galaxies according to their shape including spiral, elliptical, and irregular galaxies.
Some galaxies consist of nebulas and star clusters.
Nebulas are large cloud of gas and dust.
Globular clusters are tightly grouped stars.

43. Galaxies
Open clusters are closely grouped stars.
Scientists look at distance galaxies to learn what early galaxies looked like.