Download Chapter 21 notes - Clinton Public Schools

Chapter 21: Astronomy Notes
Section 1: Telescopes
*Light is a form of Electromagnetic radiation, energy that can travel through space in waves
*Telescope is a device that makes distant objects appear closer
*Objects in space give off all types of electromagnetic radiation
* Wavelength is the distance between the crest of one wave and the crest of another
* White light through a prism will produce a range of different colors with different
wavelengths, called a spectrum
*Telescopes: collect and focus light and other forms of electromagnetic radiation
* A telescope that uses lenses or mirrors to collect and focus visible light is called an optical
telescope.
*Refracting telescope uses convex lenses: a piece of transparent glass, curved so that the
middle is thicker than the edges.
*Reflecting telescope uses a curved mirror to collect and focus light:
*The largest optical telescopes today are all reflecting telescopes
*Radio telescopes: devices used to detect radio waves from objects in space: have curved,
reflecting surfaces
*Radio telescope focus radio waves the way the mirror in reflecting telescopes focuses light
waves
*Different types of telescopes collect electromagnetic radiation at different wavelengths:
visible light, ultraviolet, x-rays, gamma rays
*Observatories: a building that contains one or more telescopes:
*Observatories:
Located on mountaintops or in space: Earth’s atmosphere can make objects in space appear
blurry:
Sky is clearer: not brightened by city lights
*Telescopes in space: X-rays, gamma rays and some ultraviolet radiation are blocked by Earth’s
atmosphere, so to detect these wavelengths, astronomers placed telescopes in space:
Earth’s atmosphere also interferes with the transmission of visible light and infrared light
Hubble: reflecting: visible light: also collects ultraviolet and infrared
Chandra X-ray Observatory produces images in the x-ray portion of the spectrum: much
more detailed than earlier x-ray telescopes
Compton: detects gamma rays
Spitzer: produces images in the infrared portion of the spectrum
Section 2: Characteristics of Stars:


Groups of stars that form pictures of animals or people are called constellations.
Astronomers use the patterns of the constellations to locate objects in the night sky
Stars are classified according to their physical characteristics:
color: Coolest stars appear reddish, longer wavelengths, hottest stars appear blue. Our
sun appears yellowish
temperature: coolest stars about 3200 degrees Celsius: Yellow stars: 5500 degrees
Celsius: hottest stars: over 20,000 degrees Celsius, appear blue
size: Neutron stars, white dwarfs, medium size stars, giant stars, supergiant stars
composition: Stars vary in chemical composition:
A spectrograph is a device that breaks lights into colors and produces an image of the
resulting spectrum: gases in the star’s atmosphere absorb some wavelengths of light
produced within that star.
When the star’s light is seen through a spectrograph, each absorbed wavelength is
shown as a dark line on a spectrum
Each chemical element absorbs light at particular wavelengths: so each has a unique
set of lines for a given temperature: Figure 6, page 718
By comparing a star’s spectrum with the spectrums of known elements, astronomers
can infer how much of each element is found in the star
brightness: brightness depends on both its size and temperature
PHOTOSPHERE: THE LAYER OF A STAR THAT GIVES OFF LIGHT
How bright a star looks depends on both its distance from Earth and how bright the
star really is.
Apparent Brightness: is its brightness as seen from Earth
Absolute Brightness: brightness the star would have if it were a standard distance from the
Earth: more complex to find absolute brightness
astronomers must find out both the star’s apparent brightness and its distance from the
Earth
Measuring Distance to Stars:
 light year: unit to measure distance between stars: light travels at a speed of about
300,000km/sec;
 light year is the distance light travels in one year. 9.5 million million kilometers
 Parallax: astronomers often use parallax to measure distance to nearby stars
parallax is the apparent change in position of an object when you look at it from different
places.
Astronomers look at a nearby star when Earth is on one side of the moon.
They look at the same star six months later, when Earth is one the opposite side of
the star. They can then measure how much the nearby star appears to move against a
background of stars that are much farther away. The less is moves, the farther away it
is.
Can be used to measure distances up to a few hundred light years from Earth
Hertzsprung-Russell Diagram: was used to find out if temperature and absolute brightness of
stars are related.
Use HR diagram to classify stars and to understand how stars change over time.
Most of stars form a diagonal area called main sequence: More than 90% of all stars
are main sequence.

Section 3 Lives of Stars:
Nebula: large cloud of gas and dust spread out in an immense volume. A star is made up of large
amount of gas in a relatively small volume.
In the densest part of the nebula, gravity pulls the dust and gas together forming a
contracting could of dust and gas with eventually enough mass to form a star called a
PROTOSTAR
Earliest stage of a star’s life
A star is born when the contracting gas and dust from a nebula become so dense and hot that
nuclear fusion begins. Atoms combine to form heavier atoms.
How long a star lives depends on its mass: MORE MASS, SHORTER THEY LIVE…LESS MASS
THE LONGER THEY LIVE….
DEATHS OF STARS: After a star runs out of fuel, it becomes a white dwarf, a neutron star, or
a black hole, depending on its mass.
All main sequence stars eventually will become red giants or supergiants
*White Dwarfs: low mass stars and medium mass stars like the sun take billion of years to use
up their fuel: as they start to run out their outer layers expand, and they become red giants.
Eventually the outer parts grow larger still and drift out into space, forming a glowing cloud of
dust and gas called a planetary nebula. The blue—white core of the star that is left behind
cools and becomes a white dwarf…
White Dwarf: size of Earth: as much mass as sun: when it stops glowing it become a black
dwarf
Supernovas: high mass star: quickly evolve into supergiants: explosion: some materials from
the star expand into space. May become part of a nebula…this nebula can contract to form a
new partly recycled star. The sun began as a nebula that contained material from a supernova
Neutron stars: after supergiant explodes, material may form neutron star. Smaller and
denser than white dwarfs: can contain 3X mass as the sun.
Neutron stars can also be called pulsars because the rapidly spinning neutron star is
spinning hundreds of times per second, sending pulsating radio waves: pulsars are short for
pulsating radio waves.
Black Holes: most massive starts, those having 40 times more mass than the sun may become
black holes when they die.
Black hole is an object with gravity so strong that nothing, not even light, can escape.
Section 4: Star Systems and Galaxies:
Most stars are members of groups of two or more stars, called star systems:
Multiple star systems:
Binary stars: systems with two stars are called binary. Even when two stars cannot be
found, the dimmer star can be detected by observing the effects of its gravity: a wobble back
and forth
Eclipsing binary: a system in which one star periodically blocks the light from another. so
one seems to dim regularly
Star Clusters: many stars belong to larger groupings called star clusters: all formed from
the same nebula at about the same time and about the same distance from the Earth.
two major types:
* open clusters: loose, disorganized appearance and contain no more than a few thousand
stars. They often contain many bright supergiants and much gas and dust.
*globular clusters: large groupings of older stars: round, densely packed with some
containing more than a million stars.
*galaxies: huge group of single stars, star systems, star clusters, dust, and gas bound
together by gravity.
3 types:
spiral galaxies: bulge in middle and arms that spiral outward, like pinwheel. Most new
stars form in these spiral arms
elliptical galaxy: like round flattened balls, contains billions of stars, but have little gas
and dust between the stars: stars are no longer forming in elliptical galaxies.
Irregular Galaxies: do not have regular shape: typically smaller, have many bright, young
stars and lots of gas and dust to form new stars.
Quasars: objects very bright, very far away: active young galaxies with giant black holes
at their center: an enormous amount of gas revolves around the black hole, heats up and shines
brightly.
***Milky Way: spiral galaxy: recent evidence suggests that the Milky Way is a barred-spiral
galaxy instead. Lots of dust and gas.
Universe: All of space and everything in it. Numbers astronomers use are either very small or
very large: scientific notation is useful in astronomy
Section 5: The Expanding Universe:
How the universe was formed: Astronomers believe the universe was incredibly hot and
dense, exploded in what astronomers called the Big Bang.
According to the big bang theory, the universe formed in an instant, billion of years ago,
in an enormous explosion. Since then, the universe has been increasing rapidly
As universe expanded, it gradually cooled, and after a few hundred thousand years, atoms
formed. Approximately 200 million years after Big Bang, the first stars and galaxies formed.
Hubble’s Law: the farther away a galaxy is, the faster it is moving away from us. This
law strongly supports the Big Bang Theory.
Cosmic background radiation: thought to be the leftover thermal energy from the big
bang: energy was distributed in every direction as universe expanded
Age of the Universe: can measure approximately how fast the universe is expanding now,
they can infer how long is has been expanding. Careful measurements of how fast distant
galaxies are moving away from us and the cosmic background radiation, estimates are that the
universe is about 13.7 billion years old.
Formation of Solar System:
Solar nebula: about 5 billion years ago, a giant cloud of gas and dust collapsed to form our
solar system. Like the one that formed our solar system: called a solar nebula:
Planetesimals: in the outer parts of the disk, gas and dust formed small asteroid like and comet
like bodies called planetesimals: building blocks of the planets: collided and grew larger by
sticking together.
Inner Planets: When solar system formed, temps were very high…so hot close to the sun that
most of the water and other ice forming materials vaporized: most gases escaped the gravity
of the planets that were forming in this region. Inner planets: small and rocky
Outer Planets: farther from sun, much cooler: planets in this region grew, their gravity
increased and they were able to capture much of the H and He gas in surrounding space: as
result most out planets are very large:
Future of the Universe: General conclusion is that universe will continue to expand
forever.
Dark Matter: matter that does not give off electromagnetic radiation. Cannot be seen
directly: must be measured indirectly with the effect of gravity on light
Dark Energy: the possible force that accounts for the expansion of the universe