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.
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
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.
13.
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.
15.
16.
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
18.
19.
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?
22.
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
26.
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.