Transcript Ch.6 lecture

Light and Telescopes
A Telescope is a tool
used to gather light from
objects in the universe
There are two different types of
telescopes
• A refracting telescope uses a glass lens to
concentrate incoming light
• A reflecting telescope uses mirrors to
concentrate incoming starlight
Three main functions of a telescope
Most important!!
• Gather More Light – (bigger = better) making
objects appear brighter
followed by
• to see fine detail
(called resolution)
and least important,
• magnify
magnification = (objective lens focal length / eyepiece lens focal length)
A larger objective
(lens or mirror)
provides a
brighter (not
bigger) image
If you pass white light through a prism,
it separates into its component colors.
long wavelengths
R
O
Y
G
B
I
V
short wavelengths
spectrum
But visible light is only one
type of electromagnetic
radiation (light) emitted by
stars
Astronomers are interested
in the entire spectrum of
Light!
Consider This Class as Seen in Different Wavelengths of Light!
Consider Orion as Seen in Different Wavelengths of Light!
Observations at other wavelengths are
revealing previously invisible sights
UV
Ordinary
visible
infrared
Map of
Orion
region
Hubble Space Telescope Views of Orion Nebula showing stars hidden in clouds
http://oposite.stsci.edu/pubinfo/pr/97/13/A.html
Sun as seen in visible light from Earth and from space
in X-rays by satellites
http://solar.physics.montana.edu/tslater/real-time/
Radio telescopes
The Very Large Array (VLA) in New Mexico
‘Twinkle, twinkle, little star’
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Atmospheric seeing
How can we improve the image quality?
1. Bigger telescope mirror
2. Location, location location! (mountain tops, space)
3. Adaptive optics
The planet Uranus imaged in the infrared
Earth’s atmosphere refracts light: images are blurry!
Image of stars taken
with a telescope on
the Earth’s surface
Same picture taken with
Hubble Space Telescope
high above Earth’s blurring
atmosphere
The Hubble Space Telescope is in space for 2 reasons:
•
refraction (bending of optical starlight)
•
absorption (of near ultraviolet and infrared)
visible
Near infrared
Some EM radiation is absorbed by Earth’s atmosphere.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Tutorial: Telescopes and Earth’s
Atmosphere pg. 43
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with one
another. Take time to understand it now!!!!
• Come to a consensus answer you both agree on.
• If you get stuck or are not sure of your answer, ask
another group.
Which is the correct reasoning for why a gamma ray
telescope located in Antarctica that is to be used to
look for evidence of black holes in the centers of
galaxies would not get funded?
1. There is no way to detect the presence
of a black hole.
2. Gamma rays are too energetic to detect
with a telescope.
3. You can’t build a functioning telescope
in Antarctica.
4. Gamma rays don’t penetrate Earth’s
atmosphere.
Imagine you’re the head of a funding
agency that can afford to build only one
telescope. Which of the three proposed
telescopes below would be best to support?
1. A gamma ray telescope in Antarctica
2. A radio telescope in orbit above the
Earth
3. A visible telescope located high on a
mountain in Peru
4. An ultraviolet telescope located in the
Mojave desert
Imagine that you throw a ball directly upward. Which
of the following statements best describes how
Newton’s second law accounts for the motion of the
ball when it reaches its maximum height?
1.
2.
3.
4.
5.
The ball has a velocity that is zero and an
acceleration that is zero.
The ball has a velocity that is upward and an
acceleration that is downward.
The ball has a net force that is downward and a
velocity that is downward.
The ball has a net force that is downward and an
acceleration of zero.
The ball has a net force that is downward and an
acceleration that is downward.