Download Ch 3 Sec 1 Tools of modern astronomy

Ch 3 Sec 1 Tools of modern astronomy
I.
Constellations
A. Stars that are in the same direction, and form
the outline of a pattern
B. May be very different distances from Earth
II.
Electromagnetic radiation
A. Types of electromagnetic radiation
1. What you see is “visible light”
2. Electromagnetic radiation is energy traveling
through space in the form of waves
B. The electromagnetic spectrum
1. The distance between one wave and the next
is the “wavelength”
a) From as short as one millionth of a
meter to as long as several meters
2. Light can be split into different colors, each
with different wavelengths, called the
spectrum
a) Visible light spectrum is red, orange,
yellow, green, blue, and violet
3. Electromagnetic spectrum, from longest to
shortest, is radio waves, infrared radiation,
visible light, ultraviolet radiation, X-rays, and
gamma rays.
III. Telescopes
A. Purpose is to collect and focus electromagnetic
radiation, including visible light.
B. Visible light telescopes
1. Refracting telescopes are straight through,
usually with a convex lens at each end
a) The length of the tube depends on the
focal length of the objective lens
2. Reflecting telescopes use a mirror instead of
an objective lens
a) All the big telescopes now are reflecting
C. Radio telescopes
1. Use radio waves the same way reflecting
telescopes use visible light
2. The dish may be bigger than 3 football fields
D. Other telescopes – there are instruments to
capture all parts of the electromagnetic spectrum
IV.
V.
Observatories
A. Buildings housing one or more telescopes
B. Visual light observatories are up on mountains
1. Atmosphere makes images blurry
2. City lights interfere with images
C. Radio telescopes can be anywhere – light doesn’t
matter to them
Satellites
A. Atmosphere blocks much UV, X-ray, & gamma ray
radiation, so have to put telescopes above the
atmosphere to study these parts of the
electromagnetic spectrum
B. Hubble Space Telescope uses a 2.4 m mirror
1. You’ve seen its images on NASA’s web site
VI.
Spectrographs
A. Breaks light into a spectrum and records the
colors. (“Spectrograph” means recording of the
spectrum)
B. Tells astronomers about chemical composition and
temperature
C. Chemical composition
1. Different elements absorb different parts
of the spectrum
2. Where light is absorbed, there is a dark bar
in the spectrum, so that element must be
present in the star’s atmosphere
D. Temperature
1. The strongest line for an element depends
on temperature, so the presence or absence of
a strong line tells something about temperature
Ch. 3 Sec 2 Characteristics of stars
I.
Galaxies and universe
E. A galaxy is a collection of stars – hundreds of
billions of stars each
F. There is lots of nearly empty space inside and
between galaxies
1. Light takes 8 minutes to get here from the
sun (so the sun is 8 light-minutes away)
2. Light from the nearest star takes 4.2 years
(so distance is 4.2 light-years)
3. Light from the center of our galaxy takes
25,000 years to get here
4. Light from the next galaxy takes 2,000,000
years to get here
G. The universe is all of space
VII. Distances to stars
A. Measured in “light-years” – how far light travels in
one year (about 9,500,000,000,000,000 kilometers)
VIII. Measuring distances to stars
A. Astronomers use “parallax” to measure the
distances
B. Parallax is the apparent change in position of an
object when looked at from two different places.
C. Commonly done by measurements 6 months apart
D. The further away, the smaller the parallax shift
(the less it appears to move)
E. Only good to about 1,000 light-years, before the
shift gets too small to measure
IX.
Classifying stars
A. Astronomers use size, temperature, and
brightness to characterize stars
B. Sizes range from supergiants, giants, medium (like
our sun), to dwarves and neutron stars (20 km in
diameter)
C. Color tells you how hot a star is – cooler stars are
red, middle are white, and hottest are blue-white
D. Brightness depends on both size and temperature
1. A cool star won’t give off much light, but if
it’s huge, will appear bright to us.
2. Apparent magnitude is how bright it appears
from Earth
a) Depends on how close it is to Earth
b) A flashlight doesn’t change, but will look
much brighter to you if it’s in your face
than a block away
3. Absolute magnitude is how bright the star
would be at a standard distance
E. Hertzsprung-Russell diagrams
1. Graphs brightness against surface
temperature
a) Note that the X-axis is backwards –
gets smaller as you go right.
2. 90% of all stars are main sequence, which line
up diagonally on an H-R diagram
Ch. 3 Sec 3 Lives of stars
I.
Pulsars are neutron stars which are
pulsating radio sources
X.
Star is born
A. The earliest stage starts with a bunch of gas and
dust gathered together, called a nebula
B. As gravity starts to pull the gas/dust together, it
is called a protostar
C. The star is born when the gas/dust becomes so
compacted and hot that nuclear fusion starts
XI.
Lifetime of stars
A. Depends on how massive the star is
B. The more mass, the shorter its life.
1. Smallest 200 billion years; sun-sized 10
billion years; largest only 10 million
2. Smaller stars don’t burn up their fuel as
rapidly
XII. Deaths of stars
A. As they die, all stars become red giants or
supergiants
1. The core is being used up, so gravity is not
strong enough to hold the outer part, so it
expands.
B. Small and medium stars lose the outer part (it
drifts away eventually) leaving only a core about the
size of Earth, called a white dwarf
1. Even though it is very small, the white dwarf
still has about as much mass as the sun
(meaning density is quite high)
2. When the leftover energy is gone, the light
goes out and it is a black dwarf
C. Giants and supergiants may explode, called a
supernova – is millions of times brighter, for a short
period
1. The outer layer drifts away and may form a
new nebula, and eventually be part of a new star
2. What’s left is smaller and denser than a
dwarf. It’s called a neutron star. May be 3X as
massive as our sum, but only 20 km across
D. The biggest stars, more than 40X the sun, leave
behind a black hole
1. There is no hole – it just looks like one
2. The star is so massive that its gravity is
extremely high and nothing, not even light, can
escape the gravity.
3. Commonly detected by finding X-rays
emitted from gas being sucked into a black hole
a) Also, can measure its effect on a nearby
star
E. Quasars are extremely bright but extremely far
away. Astronomers think they are galaxies with
huge black holes in the center, which are sucking in
huge amounts of space gas.
Ch. 3 Sec 4 Star systems and galaxies
I.
Star systems and planets
A. More than 1/2 of all stars are in star systems –
groups of 2 or more stars
1. Systems with 2 stars are binary stars
a) A dark star may show itself by passing in
front of the brighter star – called an
eclipsing binary
b) Or, the brighter star may appear to
wobble, as the 2 stars pull on each other
2. Planets have been found around other stars
a) Same techniques as used for binary star
systems
b) Means that can’t find planets as small as
Earth – ones found so far are at least 1/2
the size of Jupiter
XIII. Galaxies
A. Milky Way looks milky because the stars are too
close together to been seen individually
1. Our sun is far out on one arm of the Milky
Way
B. Spiral galaxies are relatively flat, with arms going
out like pinwheels
1. These have lots of gas and dust in the
center, so they are still making new stars
C. Elliptical galaxies look like flattened balls
1. There is little gas and dust, so no new stars –
only old stars
D. Irregular galaxies are those with no regular shape
Ch. 3 Sec 5 History of the universe
I.
Moving galaxies
A. They are all moving. A few close ones are coming
closer, but most moving away from us
B. The further out a galaxy is, the faster it is
moving away from us
1. Means that the universe is expanding
II.
Big bang theory
A. If you could run time backwards, galaxies would all
be moving closer together, until they were all at a
single point.
B. The explosion that started the outward motion
happened about 10-15 million years ago
1. Knowing how fast it is expanding allows you to
calculate how long it has been expanding
III. Formation of the solar system
A. About 5 billion years ago, a nebula started to
collapse to form the solar system
B. Started forming a spinning disk
C. Gas in the center condensed into the sun
D. Other bits of gas and dust gathered into the
planets
E. The inner planets lost their gases to the sun’s
gravitational pull
IV.
Future of the universe
A. Could continue to expand until the stars all use up
their fuel and the universe goes dark and cold.
B. Another possibility is that gravity will eventually
stop the expansion and start sucking everything
back to the center – could be the “big crunch”, the
opposite of and beginning of the big bang
C. Which will happen depends on how much matter
there is in the universe (because more mass means
more gravity), so astronomers are looking for dark
matter between stars systems. They are finding
quite a bit of it.