Grade 8 Integrated Science Chapter 12 Lesson 1 on the view of space from Earth. This lesson gives a short introduction on constellations, relative brightness, luminosity, and the apparent size of a star. *This version (Version 2) contains pictures and diagrams of 3 constellations and a white background for easier viewing.

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.