1. Chapter 12 Lesson 1 – The View from Earth – p414-419 - page1
Vocabulary
 Spectroscope (417) – an instrument that spreads light into different wavelengths
 Astronomical Unit (418) – the average distance between Earth and the Sun, about 150
million km
 Light-year (418) – the distance light travels in 1 year
 Apparent Magnitude (419) – a measure of how bright it an object appears from Earth
 Luminosity (419) – the true brightness of an object
Looking at the Night Sky
 If you look at the stars for a long time they seem
to________________.
 ________________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.
 Polaris is commonly referred to as
the___________________________,
because it and the stars near it never
___________when viewed from the
northern hemisphere.
Naked-Eye Astronomy
 Naked-eye astronomy means gazing at the sky using just your eyes; no
___________________ or telescopes.
 Before telescopes, people used the stars to tell time, ___________________, and finding
directions.
Constellations
 When ancient cultures gazed at the night sky, they saw_______________________.
o They represented people, animals, and objects
 The Greek astronomer Ptolemy identified dozens of star patterns nearly
______________ years ago.
o These are called ________________ ____________________today
 Present-day astronomers use many ancient constellations to divide the sky
into ______________regions also called constellations
Telescopes
 Telescopes are able to collect much more _____________________than the human eye
 The _______________________ spectrum is a continuous range of wavelengths
o __________________ light is only one part of the spectrum

2. Chapter 12 Lesson 1 – The View from Earth – p414-419 - page2
o Longer wavelengths have ______________energy
o Shorter wavelengths have ______________energy
 Different objects in space can emit different types of wavelengths.
 The range of wavelengths a star emits is called its__________________________.
Spectroscopes
 Scientists study the spectra of a star using a___________________________________.
 A spectroscope ___________________ light into different wavelengths.
 This way, scientists can study a star’s characteristics, compositions, and______________.
 Newly formed stars emit mostly _____________and infrared waves. While exploding stars
emit high energy _______________________________waves.

3. Chapter 12 Lesson 1 – The View from Earth – p414-419 - page3
Measuring distance
 Astronomers use angles created by __________________ to measure how far objects are
from Earth.
o Parallax is the apparent change in an object’s
____________________ caused by looking at it from 2
different points.
o 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
____________________ around the Sun
Distance Within the Solar System
 Distances ________________ the solar system are measured using astronomical units or
AU.
 An astronomical unit is the average distance between Earth and _____________________ ,
about 150 million km.
Distances Beyond the Solar System
 Astronomers measure distances ___________________ the solar system using light-years.
o A light-year is the distance light travels in 1 year.
o 1 light-year equals about 10 _______________________km.
 The nearest star to our Sun is 4.2 light-years away. How far is that in km?
Looking Back in Time
 Because it takes time for light to travel, you see a star not as it is______________, but as it
was when light left it.
 At 4.2 light-years away, Proxima Centauri appears as it was
______________ years ago.
Measuring Brightness
 Astronomers measure the brightness of stars in two ways:
o By how bright they appear from Earth
o By how bright they actually are
Apparent Magnitude
 Scientists measure how bright stars appear from __________________ using a scale
developed by the ancient Greek astronomer Hipparchus
o Hipparchus assigned a _______________ to every star he saw in the night sky based
on its brightness.
 Today these are called __________________ _____________________
o The apparent magnitude of an object is a measure of how bright it appears from
Earth
 Hipparchus assigned the number __________ to the brightest star he saw in the night sky

4. Chapter 12 Lesson 1 – The View from Earth – p414-419 - page4
Absolute Magnitude
 Stars can appear bright or dim depending on their __________________ from Earth, but
stars also have actual, or absolute, magnitudes
 __________________________is the true brightness of an object
 This depends on the star’s _____________________and size rather than its distance from
Earth
 A star’s luminosity, distance, and apparent magnitude are all_____________________.
Thus, if a scientist knows two of these factors, he can mathematically determine the third.
Apparent Magnitude Scale