1. Astronomers Observe Light Radiated Toward Earth By Matter in Space
2. Light is Energy That is Radiated as a Wave with both Electric and Magnetic
Properties
3. The Electromagnetic Spectrum Shows All Light Grouped in BANDS organized
by wavelength
Short wavelength
High energy
Long wavelength
Low energy
All light travels through space at the same speed -The Speed of Light -- 300,000 kilometer/second !!!
The distance light travels in one year is called a Light
Year -- about 10 trillion kilometers
Our galaxy -- the Milky Way -- is about 100,000 light
years in diameter and contains more than 200 billion
stars!!
The nearest star system to our Sun is Alpha Centauri -about 4.2 light years away!! How many kilometers is
that??
Fortunately, gamma rays, x-rays and much UV light are
absorbed by Earth's atmosphere -- sparing us from harm
Earth's atmosphere is transparent (like a window) only to
certain bands, including:
Optical Window –
some UV light, all
visible light and some
infrared light
Radio Window –
some radio waves
and some
microwaves
Galileo Improved the Refracting
Telescope to observe visible
light
Refractors use curved glass lenses to
magnify objects up to 30x
Visible light is refracted (bent) as it enters
and exits a curved glass lens
-- visible light is refracted
(bent) as it passes from air
into material of a different
density.
-- white light bent by glass
prism is spread into rainbow
-- through water too!
You can blend
colors back into
white light too!
-- Lenses
can be arranged to refract (bend) light in ways that make
objects appear larger than they are.
Convex Glass Lens
-- The lens tricks the brain into thinking
the object is larger than it is
-- Object is magnified
Chromatic Aberration is a
problem with refracting lenses
-- white light is separated into
colors of the rainbow
-- creates image blurry with
rainbows at edges
Diagram of Refracting Telescope
Sir Isaac Newton developed Reflecting
lens Telescopes
Reflector Telescopes use mirrors (instead of glass
lenses)
Two Advantages of reflecting telescopes:
of
1. No Chromatic Aberration – no separation
white light into colors of the rainbow
2. Mirrors weigh less than glass lenses
Universal Law of Gravitation
All objects in the universe exert a
force on each other that is related to
the mass of the two objects and the
distance between them
This force is gravity
Reflecting Telescope uses mirrors to gather and focus light
Mirrors focus light
by reflecting it, NOT
refracting it
Modern Telescopes Are Designed
to Observe Specific Bands of Light
Since our
atmosphere is
transparent to
Radio Waves we
can position
radio telescopes
on Earth
Arecibo Radio Telescope in Puerto Rico – located on a
mountain and dug into the ground facing up so that it
only detects radio waves from space, not radio waves
emitted by radio stations. Radio waves are very long,
so receiver must be very wide and it does NOT have to
be a smooth surface
Arecibo also emits radio waves that bounce off near-Earth
asteriods and back to the telescope so we can keep track
of how close they come to Earth!
Click here to see a
radio image of an
asteroid taken by
the Arecibo radio
telescope
The South Pole Telescope observes microwave light
from space. It is located in Antarctica because the
altitude is very high and the air is very dry. The
atmosphere on mountain tops is much thinner and thus
is more transparent to microwaves. Moisture in the air is
a very effective blocker of microwaves.
Image of the “Cosmic Microwave Background” energy
left over from the formation of the Universe 13.75 billion
years ago – aka, the “Big Bang”
Spitzer Space Telescope – designed to detect the infrared
light emitted by the cooler gas of Nebulas (the remains of
supernovae) and the rings of Jupiter, Saturn, Uranus and
Neptune
Earth's atmosphere
absorbs most
infrared light, so
infrared telescopes
are designed to
orbit Earth above
the atmosphere
Image of Saturn’s largest ring – made by Spitzer
Hubble Space Telescope has orbited above Earth’s
atmosphere for over 20 years – taking pictures of the
visible light emitted and reflected by objects in space
Although our
atmosphere is
transparent to
visible light,
Hubble takes much
clearer pictures
because it is above
the atmosphere
Hubble Ultra Deep
Field of the many
Galaxies in our region
of the Universe
SOHO Solar Space Telescope – detects UV light emitted by
the Sun
SOHO helps astronomers
predict dangerous "space
weather" caused by massive
ejections of particles and
energy by the Sun.
Space weather can cause
satellites to fall out or orbit,
expose airline passengers to
be exposed to high doses of
radiation and cause electrical
blackouts on Earth.
Image of the UV light emitted
by the Sun taken by the SOHO
space telescope, showing a
large ejection of energy and
particles in the upper right
quadrant of the Sun.
Image is colorized to help us
see different wavelengths
within the band of UV light
Chandra Space Telescope
Designed to detect X-rays
emitted by the hottest
objects in space such as
neutron stars and black
holes
All space X-rays are blocked
by our atmosphere
Infrared image of the famous “Crab
Nebula” taken by the Spitzer Space
telescope. It shows the cooler dust
swirling around the remains of an
exploded star
Image of the same “Crab
Nebula” taken by the Chandra
X-ray telescope. The central
white star spewing a jet of xrays is clearly visible
Hubble Space Telescope Video