This document provides an overview of key astronomical concepts, including the definitions of spectroscope, astronomical unit, and light-year. It explains how stars appear to move due to the Earth's rotation, the use of naked-eye astronomy for navigation, and the measurement of distances and brightness in the cosmos. Additionally, it discusses the significance of constellations and the historical contributions of astronomers like Ptolemy and Hipparchus.

1. Chapter 12 Lesson 1 p414-420
THE VIEW FROM
EARTH

2. Vocabulary
 Spectroscope – an instrument that spreads
light into different wavelengths
 Astronomical Unit – the average distance
between Earth and the Sun, about 150 million
km
 Light-year – the distance light travels in 1 year
 Apparent Magnitude – a measure of how
bright it an object appears from Earth
 Luminosity – the true brightness of an object

3. Looking at the Night Sky
 If you look at the stars
for a long time they
seem to move.
 Why does this happen?
 Polaris is a star almost
directly above the north
pole.
 As Earth spins Polaris
stays in place as stars
near it seem to circle
around it.

4.  Polaris is commonly referred to as the Northern
Star, because it and the stars near it never set
when viewed from the northern hemisphere.

5. Naked-Eye Astronomy
 Naked-eye astronomy means gazing at the
sky using just your eyes; no binoculars or
telescopes.
 Before telescopes, people used the stars to tell
time, seasons, and finding directions.

6. Constellations
 When ancient cultures gazed at the night sky,
they saw patterns.
 They represented people, animals, and objects
 The Greek astronomer Ptolemy identified
dozens of star patterns nearly 2000 years ago.
 These are called ancient constellations today
 Present-day astronomers use many ancient
constellations to divide the sky into 88 regions
also called constellations

7. ORION

8. LEO

9. SCORPIO

12. Telescopes
 Telescopes are able to collect much more light
than the human eye
 The electromagnetic spectrum is a continuous
range of wavelengths
 Visible light is only one part of the spectrum
 Longer wavelengths have low energy
 Shorter wavelengths have higher energy
 Different objects in space can emit different types
of wavelengths.
 The range of wavelengths a star emits is called its
spectrum.

14. Spectroscopes
 Scientists study the spectra of a star using a
spectroscope.
 A spectroscope spreads light into different
wavelengths.
 This was scientists can study a stars’
characteristics, compositions, and energies.
 Newly formed stars emit mostly radio and infrared
waves. While exploding stars emit high energy
ultraviolet waves.

17. Measuring distance
 Astronomers use angles created by parallax to
measure how far objects are from Earth.
 Parallax is the apparent change in an object’s
position caused by looking at it from 2 different
points.
 For example: Look at your pencil with only your left
eye. Then, without moving the pencil, look at it with
only your right eye.
 Astronomers create a parallax by using 2
points in Earth’s orbit around the Sun

20. Distance Within the Solar
System
 Distances within the solar system are
measured using astronomical units or AU.
 An astronomical unit is the average distance
between Earth and the Sun, about 150 million km.

21. Distances Beyond the Solar
System
 Astronomers measure distances beyond the
solar system using light-years.
 A light-year is the distance light travels in 1 year.
 1 light-year equals about 10 trillion km.
 The nearest star to our Sun is 4.2 light-years
away. How far is that in km?

23. Looking Back in Time
 Because it takes time for light to travel, you
see a star not as it is today, but as it was when
light let it.
 At 4.2 light-years away, Proxima Centauri
appears as it was 4.2 years ago.

24. Measuring Brightness
 Astronomers measure the brightness of stars
in two ways:
 By how bright they are from Earth
 By how bright they actually are

25. Apparent Magnitude
 Scientists measure how bright stars appear
from Earth using a scale developed by the
ancient Greek astronomer Hipparchus
 Hipparchus assigned a number to every star he
saw in the night sky based on its brightness.
 Today these are called number magnitudes
 The apparent magnitude of an object is a
measure of how bright it appears from Earth
 Hipparchus assigned the number 1 to the
brightest star he saw in the night sky

27. Absolute Magnitude
 Stars can appear bright or dim depending on
their distances from Earth, but stars also have
actual, or absolute, magnitudes
 Luminosity is the true brightness of an object
 This depends on the star’s temperature and
size rather then its distance from Earth
 A star’s luminosity, distance, and apparent
magnitude are all related. Thus, if a scientist
knows two of these factor, he can
mathematically determine the third.