Astronomy
Lecture Notes
What is the difference between astronomy and
cosmology?
Cosmology
is a branch of astronomy that studies origin, structure, and space-time
relationships of the universe. Who are the most important astronomers and what
did they discover? The Early Greeks (and Phoenicians, Egyptians) named the
stars in 88 patterns called constellations. Astronomers were the “stellar”
scientists at this time. About 300 BC, an observatory was built in
Telescopes.
The
optical telescopes (with reflecting mirrors and/or refracting lens) have been
the mainstay of astronomy for hundreds of years. Newer telescopes collect
radiation from the full electromagnetic spectrum (radio waves, x-rays, gamma
rays, ultra violet, visible light, cosmic rays). The Hubble Space Telescope
(HST), with mirrors only 2.4 m diameter, went into orbit around the earth in
1990 and provided clear pictures of the universe 3X better and further than any
telescope before its time. Its view is unobstructed by atmosphere and light
pollution. The HST uses several types of imaging and sensing devices. It has
been repaired and recommissioned to work until 2010.
New land-based telescopes are using large micro-manipulated mirrors to improve
on the HST imagery.
What are the most important facts to know about the
universe?
Our
Milky Way Galaxy, a spiral galaxy, contains over 200 billion stars, and spans
100,000 light years. Galaxies can be spiral, elliptical, or irregular. Light
travels at 300,000 km/s (3x108 m/s). A light-year is the distance
light travels in one earth year. Our solar system is 30,000 light years away
from the center of the Milky Way galaxy. Galaxies are clustered into groups
called super clusters, and these are parts of constellations. On a moonless
night away from city lights you can see a band of whitish light, which is the
disc of the Milky Way due to the large quantity of stars we cannot see
individually. There are over 100 billion galaxies, each containing over a
billion stars. Carl Sagan coined “billions and
billions and billions” of stars. A light-year is the distance light travels in
a year. Galaxies are separated by millions of light years. SETI is the search
for extraterrestrial intelligence. Galaxies form most of the visible mass of
the universe and there is black mass, which we cannot see. Astronomers have
recently discovered planets orbiting other stars. Polaris, the north star,
looks like it is always above the north pole from
anywhere on the northern hemisphere. This explains why early sea explorers were
able to navigate out of site of land and develop trade routes essential to
development of western civilization.
What are some important events with people in space?
Chuck
Yeager broke the sound barrier in the X-15, the Russian Sputnik was first in
space in 1957, Yuri Gagarin was the first man in space in 1961, Alan Sheppard
was the first American in space, John Glenn was the first to orbit Earth and
also the oldest person in space, Neil Armstrong was first on the moon in 1969,
and Sally Ride was the first woman in space.
Big bang theory and expansion of the universe was proposed by Edwin Hubble. 10 to 20 billion years
ago the universe was as small as your fist (no space or time) 10-32 seconds
after the “big bang” initial expansion at greater than the speed of light. Existence of quark soup, 6 types of subatomic particles, building
blocks of protons and neutrons. In 1 second “big freeze” occurred when
particles came together started formation of atoms (nucleosynthesis)
reducing temperature from 10 billion to 1 billion degrees, H and He start to
form 300,000 years after the big bang light and matter separated 1 billion
years after the big bang the first galaxies formed. Currently, universe is
expanding, but expansion is slowing (future expansion or collapse?) Open, flat,
and closed universes are speculated outcomes of future expansion/collapse.
Doppler affect with light used to measure movement away or toward us. Doppler effect is a shift in frequency of electromagnetic radiation
when the observer or source are moving relative to each other. Older parts of
universe are expanding away from us at faster rate than near parts. We know
this by the larger red shift in light spectrum from older parts of universe. Radiation
from big bang is still detectable.
Parallax
shift is the apparent movement of objects against each other, or a background.
Parallax is a method used to measure distances to planets and stars. We use
parallax with our bifocal vision to determine distances by comparing the L and
R eye images. Move your finger or pencil 20 to 40 cm away from your face and
look at it and background with right, left and then both eyes open. The closer
the object, the greater the parallax shift.
Astronomers use the star view from 6-month intervals when the earth is on
opposite sides of orbit around sun. Uses trigonometry by
measuring angles to point source from 2 locations (e.g. 2 eyes or 2 locations
of earth’s orbit). Early astronomers used parallax to determine that
planets orbit the sun rather than the earth. The largest parallax shift for the
nearest star is less than 1 arc second (diameter of a dime at 1 mile distance)
= 1 parsec away = 3.26 light years. Galileo tried to use parallax in 1609 to
determine star distances but found his telescope was not able to observe the
small shifts in parallax. The first star parallax was measured in 1838
independently by 3 scientists. Hendersen’s meridian
circle was the most practical and popular. Photography was introduced in 1888.
Stars – life cycles.
How do visual,
radio and X-ray telescopes collect data?
We
collect data on stars using visual, radio, and X-ray telescopes. Stars start as
nebula, a clump of gas (mostly H and He) and dust to coalesce into a prostar. When critical mass reached, then fusion begins (H
combines into He). Most are in binary systems (2 or more suns) and are in “main
sequence”. Main sequence of star life (90% of stars) is large blue sun, smaller
yellow sun (our sun is a G2 star). When H is used up and only He left, star
swells into red giant whose core collapse into a white dwarf (outer material
blown away in supernova), becoming a dead star (neutrons only) or black hole. Supergiant– extra large star (300 times size of our sun)
that is short-lived. The Hertzsprung-Russel Diagram
shows relationship of absolute magnitude, luminosity, and star temperature.
Stars have different colors (related to temperature) and their brightness,
compared to our sun, is its luminosity. Surface temperatures range form 2,800
(red stars) to 28,000 degrees C (blue stars). Some stars pulsate = Cepheid
Variables e.g. Polaris (North Star). Quasars are oldest objects in universe and
are near edge of universe, 12 billion light years away, they give off radio
waves and more energy than 100 galaxies combined. Inside the star, heavier
elements get created through fusion. During a supernova, elements heavier than
lead (Pb) are formed and distributed throughout the
universe.
Composition of the sun and nuclear
energy generation.
Diameter
864,000 mi., core is at least 27 million degrees, rotates every 25-36 days. Over
1 million earth planets would fit inside it, contains over 98% of mass in solar
system H (92%) and He (7.8%) make up most of sun. Fusion is nuclear
transformation; primarily 2 H become 1 He, releases energy Temperature at the
core is 15 million degrees C and at the outer layer only 2 million degrees C
and at the surface the temperature drops to 6000 degrees C. It takes 1 million
years for energy to escape the sun core to reach its surface. Sunspots – dark
spots on sun surface, cooler than other areas of sun. Solar flares – outbursts
of light and energy. Solar wind – emission of subatomic particles, mostly
protons, and cause the comets tails to point away from the sun. Seven layers:
He core, radiative zone, convective zone, photosphere, chromosphere
and corona. Energy enters the earth system primarily as solar radiation and
eventually escapes as heat. Sun energy (not earth core heat) is the primary
source of energy and heat on the surface of the earth. Sun energy reaching earth – 34%
reflected, 42% heating, 23% evaporation, 1% waves and wind, 0.023%
photosynthesis, energy cycles through earth’s biogeochemical systems.
Solar system formation and material
composition.
Started 5 billion years ago from nebula of gas, ice,
and dust. Planets formed 4.6
billion years ago. Heavier metals ended up nearer the sun, condensing to form
rocky planets consisting of iron, silicon, magnesium, sulfur, aluminum, calcium
and nickel. Heavy metals sank to the cores and light materials went to the
surface. The early atmospheres of the inner planets blew away with solar wind.
500 million years ago, solar system was in its current form.
The
planets, comets, asteroids, dust and gases orbit the sun in ellipses, but
earth’s ellipse looks more like a circle. Radial orbital distances of planets,
asteroids, and comets are sometimes measured in astronomical units (AU), the
radial distance of earth’s orbit.
What are the planet's names? 3rd rock from the sun?
Mercury,
Venus, Earth, and Mars are solid. Jupiter, Saturn, Uranus, Neptune are gaseous.
Pluto may be an escaped moon.
·
Mercury’s
magnetic field is 1% as strong as earth’s. It is a rock planet composed mostly
of iron and nickel. It has a thin atmosphere of H, He, K, and S compounds.
·
Venus is the
closest planet to earth and has similar size and composition. It has a CO2
atmosphere. Its surface has volcanic activity and is pot marked with craters.
·
Earth has a
high content of radioactive uranium, thorium and potassium so its interior is
hot, even after cooling for over 4 billion years.
·
Mars is 1/3
the size of earth and is composed of iron and iron sulfides. The outer surface
is oxidized (rusted) and looks red. Its magnetic field is too weak to measure.
The Pathfinder landed there in 1997. Mars may have had primitive life on it 3
billion years ago, but is unlivable now.
·
Jupiter is
composed mostly of H and He gas and is larger than all
the other planets combined. The Great Red Spot is a giant cyclone storm at
least 2 times the size of earth. In 1994, a large comet crashed into Jupiter.
·
Saturn is a
large gas planet composed of H and He. It has a
magnetic field 1000X stronger than earth. The A and B rings are actually
thousands of rings with ice and ice-covered particles.
·
Uranus and Neptune are both gas planets and look blue because of their methane gas
atmospheres.
·
Pluto is a
tiny low-density planet composed mostly of nitrogen.
The 4
inner planets have different atmospheres in depth and composition. Earth is the
only one with a substation amount of oxygen. Remember the greenhouse effect and
global warming. Why does Venus have the highest temperature and not Mercury?
It’s the gas.
The
main dark shadow of solar eclipse = umbra, the lighter part of shadow =
penumbra.
Nebula
theory – solar system formed at same time from a gas cloud
99% of
the gas became the sun and fusion started.
How are we currently exploring the universe?
Optical
and radio telescopes, artificial satellites and probes, and the international
space station (being built). SETI – search for extraterrestrial intelligence. NASA – National Aeronautics and Space Administration. Mercury
and Gemini missions put men into space, Voyager mission sent probes into deep
space, Apollo put man on the moon. The Apollo 11 fire,
Apollo 13 disaster/miracle (great movie) and the Challenger explosion (teacher
on board) had major impacts on the public, NASA and the space program. Hubble telescope – large telescope in space, no light pollution or
atmospheric interference. Pioneer and Voyager were early interplanetary
explorations. Magellan probe mapped Venus. Pathfinder robot
landed on Mars in 1997, 2 probes in 2000 were destroyed.
Asteroids
and their impact on planets, especially recent one being currently studied (vs.
comets)
Comets
are made of dust, loose rock, frozen water, methane, and ammonia. There is a
large spherical cloud of comets outside of Pluto, the Oort
Cloud. They have elliptical orbits around the sun and
eventually lose all their material (vaporize). Comet
tails always point away from the sun due to solar wind (particles expanding
away from sun). Meteors burn up in the atmosphere, meteorites hit the ground (-ite means rock). Pea size meteors impact earth at the rate
of 10 per hour. Meteors burn up in about 1 sec leaving a fiery streak (shooting
star). Most of our atmospheric dust is attributed to space debris. What
materials are asteroids made of? Rock, metal (iron and
nickel). Asteroids are from 100 feet to several miles diameter. Most are
located in the asteroid belt between Mars and Jupiter about 245 to 580 million
km from sun, but also many in orbits around sun closer or farther than earth
and some pass through earth’s orbit (e.g. Apollo, Amor
and Athens Group). Over 1000 asteroids > 1 km diameter
cross earth’s orbit. Where did they come from? Broken up planet is one
hypothesis. What size of asteroid can do real harm to the Earth? 1 mile wide. What asteroid is currently being probed by
NASA? 433 Eros (also Gaspra, Ida, and Mathilde) is being studied by the NEAR probe (Near Earth
Asteroid Rendezvous). Eros has a 50% chance of hitting the earth in next 100
million years. Asteroids hit Earth all the time; most are small and burn up in
the atmosphere. The last large one was 2,000 years ago and left a ¾ mile wide
crater in
Earth development over last 6 billion
years (change in composition and
structure).
Gas
cloud coalesced into molten rock. First million years there were many volcanoes
spewing lava, ash, and water (created oceans). One theory of ocean development
is that water came from ice comets. Earth has a solid inner core (3,500 km
thick) mostly Fe and Ni due to high pressure. Mantle (3,500 km thick) is like
silly putty, solid but plastic and moving like a liquid. Crust is only 60 km. Eras
on earth: Precambrian (unicellular organisms developed), Paleozoic (fish and
amphibians, Pangaea formed), Mesozoic (Triassic, Jurassic, Cretaceous periods,
dinosaurs, angiosperms) and Cenozoic (mammals). The Precambrian takes up more
than the first 4 billion years of the earth’s 4.6 billion year existence. The
ice age occurred 45 million years ago and may be the result of CO2 depletion
(less greenhouse effect) due to uplifting and weathering of the seabeds (chemical reactions in the limestone) to create the
Himalayan Mts. (collision of Indian and Asian tectonic plates). Homo sapiens
developed 500,000 years ago and became dominant only 10,000 years ago, a speck
of a second in geologic time. The current time period is the Quaternary Period.
Blue green algae fossils found in rock 3 billion years old. Living Xenophile
bacteria found in deep rock mining cores today. Early life believed to be
formed from self-replicating molecules in primordial soup with UV sunlight and
lightning providing energy. Continents
were all connected as one, Pangaea, and then drifted into 2 continents,
Gondwanaland and Laurasia. These in turn broke up
into our present 6 continents.
Earth’s earliest atmosphere (H and He similar to other planets) was swept away by
solar wind since these gases were so light. Volcanoes spewed water vapor, CO2,
methane and nitrogen gases. As earth crust cooled, water condensed forming rain
and filling the oceans. The CO2 dissolved into the water (chemical buffering)
leaving mostly N2 in the air. One small source of O2 was the breakup of H2O by
UV light. The major source was life forms (cyanobacteria)
broke up CO2 into C and O2, keeping the carbon and releasing the oxygen (a
waste product). Carbon now cycles through the biogeochemical spheres.