1. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Section 3 Mapping the Stars

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Section 3 Mapping the Stars Explain how constellations are used to organize the night sky. Describe how the altitude of a star is measured. Explain how the celestial sphere is used to describe the location of objects in the sky. Compare size and scale in the universe, and explain how red shift indicates that the universe is expanding. Objectives

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Section 3 Mapping the Stars Patterns in the Sky Constellations Help Organize the Sky A constellation is a region of the sky. Each constellation shares a border with neighboring constellations. A constellation map is shown on the next slide. Seasonal Changes As Earth revolves around the sun, the apparent locations of the constellations change from season to season.

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Spring Constellations in the Northern Hemisphere Section 3 Mapping the Stars

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 The sky is divided into 88 constellations Mesopotamia, circa 3000 BC: oldest know constellations Ptolemy, 2nd century AD: 48 constellations in northern sky 16th to 18th century AD: unmapped regions of sky filled in

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Constellations are largely arbitrary Other cultures, other constellations: Example: Ursa Major = bear, dipper, bull's leg, grain scoop, wagon, plow, etc. Stars in a constellation usually are not at the same distance from us. At a different place in our Galaxy, we would see different star patterns.

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 A modern star chart of Ursa Major:

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26. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Section 3 Mapping the Stars Finding Stars in the Night Sky You can describe the location of a star or planet by using an instrument called an astrolabe and the following points of reference: The zenith is the point in the sky directly above on observer on Earth. The altitude is the angle between an object in the sky and the horizon. The horizon is the line where the sky and the Earth appear to meet.

27. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Section 3 Mapping the Stars Altitude, Horizon, and Zenith Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

28. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Zenith, Altitude, and Horizon Section 3 Mapping the Stars

29. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Azimuth – measured in degrees – how far from North an object is.

30. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Section 3 Mapping the Stars Finding Stars in the Night Sky, continued Using an astrolabe allows you to describe where a star or planet is relative to you. Scientists need a different method that describes location independently of the observer’s location. Astronomers describe the location of a star or planet in terms of the celestial sphere.

31. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 The Celestial Sphere Section 3 Mapping the Stars

32. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Section 3 Mapping the Stars Describing a Star’s Position Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

33. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Stars are “attached” to a celestial sphere Distances to stars are hard to measure. However, we can pretend all stars are at the same distance from us, attached to a large celestial sphere. Position on the celestial sphere is known even when the distance in unknown.

34. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Celestial Sphere: A large imaginary sphere centered on Earth

35. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Special locations on the celestial sphere North Celestial Pole = point directly above Earth’s North Pole (near the star Polaris) South Celestial Pole = point directly above Earth’s South Pole (no nearby bright star) Celestial Equator = circle directly above Earth’s Equator

36. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Distances between points on the celestial sphere are measured in degrees, arcminutes, and arcseconds 360 degrees in a circle 60 arcminutes in a degree 60 arcseconds in an arcminute ½ degree = angular size of Sun & Moon

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38. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Celestial navigation made simple At Earth’s North Pole: Polaris is directly overhead At Earth’s Equator: Polaris is due north, on the horizon In Earth’s Northern hemisphere: Polaris is due north - height above the horizon (in degrees) is equal to your latitude (in degrees)

39. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 The celestial sphere appears to rotate about the celestial poles (1 day cycle) Observation: Stars, Sun, Moon and planets move in counterclockwise circles around north (south) celestial pole. Objects near the celestial equator move east to west when above the horizon (“rising” in east, “setting” in west). What causes these circular motions?

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42. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Section 3 Mapping the Stars Circumpolar Stars Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

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49. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 The Sun appears to move west to east relative to stars (1 year cycle) Today the Sun is “in” Sagittarius, next month in Capricornus, etc. Sun’s path on the celestial sphere = ecliptic Constellations through which the ecliptic runs = zodiac The ecliptic is NOT the same as the celestial equator!

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51. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1 Observation: Sun moves west to east relative to stars (about 1 degree per day). What causes this annual motion?

52. Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 1