Download Notes for Unit 5

Unit E: Space Exploration: Note Outline
Section 1
Sec. 1.1: Early Views about the Cosmos
-many celestial objects and events have been tracked by people for thousands of years
-this was important for the following reasons:
-agricultural: when to plant and harvest crops
-calendar: keep track of the passage of weeks, months, and days
-religious holidays: insure that people are celebrating religious holidays on the
correct days
-navigation: determine position and course
-different cultures came up with different ideas about the cosmos
-e.g.: First Nations people of the Pacific Northwest thought the sky was a pattern
on a large blanket. The blanket was held up by a spinning world pole. The bottom of the
pole rested on the chest of a woman underground named Stone Ribs.
-Stonehenge, in England, is one example of a megalith structure (large rocks set in a
pattern). It was built in at least three separate phases between around 2800 B.C. and
1800 B.C. No one is sure exactly what it was built for or who built it, though most
researchers acknowledge it was used to help tell when the solstices occurred.
-other stone formations exist in different parts of Europe as well as Africa.
Define the term winter solstice. Around what date does it occur in the northern
hemisphere?
The winter solstice is the first day of winter, around Dec. 21. It is the shortest day of the
year. Along the horizon in the months up to the winter solstice, the sun rises farther west
and sets farther east each day. That now stops (“sol” = sun and “stice” = stop), and the
sun slowly starts to rise and fall such that the days get longer.
Define the term summer solstice. Around what date does it occur in the southern
hemisphere?
The summer solstice is the first day of summer, around June 21. It is the longest day of
the year. Along the horizon in the months up to the summer solstice, the sun rises farther
east and sets farther west each day. That now stops (“sol” = sun and “stice” = stop), and
the sun slowly starts to rise and fall such that the days get shorter.
Define the term equinox. When do equinoxes occur? What are they each called?
At the equinox, the amount of daylight and nighttime hours are equal. The spring
equinox (also called the vernal equinox) occurs around March 21 in the northern
hemisphere. The fall equinox (also called the autumnal equinox) occurs around Sept.
21 or 22 in the northern hemisphere.
-many cultures, including the Egyptians, the Mayans, and the aboriginal peoples of
southwestern Alberta built structures which aligned with specific celestial objects or
events.
Planetary Motion Models
-until the 1500s, the visible sky consisted of the sun, moon, Mercury, Venus, Mars,
Jupiter, and Saturn, along with various stars.
Disclaimer:
The next section deals with the history of astronomy from Greece to Newton, a favourite
topic of mine. The book leaves out some absolutely critical events (like Ptolemy,
HELLO PEOPLE?!?!). So, I took the liberty of filling in some gaps. The stuff in italics
are things mentioned in the text; all the other things are not mentioned in the text. But, if
you want to know at least a respectable fraction of the real story, you’ll read it all.
As well, the version presented below is not only terribly annotated, but it is also terribly
Eurocentric. Some really important stuff happened in other places, including Asia, the
Islamic world (particularly in places like the House of Wisdom in Baghdad, in presentday Iraq), and in areas where prominent Jewish astronomers lived. Unfortunately, this is
a western-centered text, so that information is not provided here. Please realize this does
not mean their contributions are to be overlooked or underestimated.
Thank you 
Ancient Greece:
-some “stars” in the sky appeared to move amongst the fixed background of the other
stars. These wandering stars were called planets (after the Greek word for wanderer).
-the objects considered to be planets were: the moon, Mercury, Venus, the sun, Mars,
Jupiter, and Saturn. Note that the earth was NOT considered to be a planet.
-all heavenly bodies were considered to be spherical and perfect (no craters, etc.). This is
because the Greeks considered the sphere to be the perfect geometrical shape, and wow,
did they ever love geometry!!
-Aristotle believed that the universe was geocentric, which means earth-centered.
-Ptolemy (whom your book does not mention – some people ought to be ashamed of
themselves!!!!), who lived around 100 A.D., refined the model. His model became the
standard for almost 1400 years to come. His model consisted of:
-the earth at the center of the universe: fixed and unmoving
-surrounding the earth: the moon, then Mercury and Venus (though the order of
these two was not certain), then the Sun, then Mars, Jupiter, and Saturn.
-outside Saturn was the sphere of the fixed stars.
-all the spheres surrounding the earth turned around the earth once per day. The
spheres themselves were thought to be made of some sort of heavenly crystalline
material. All matter on earth, as Aristotle stated, was made up of the four
elements: earth, water, air, and fire. All matter in the heavens was made of the
fifth element, the ether. Space was not empty, but rather filled with this ether.
Various Greek gods were responsible for turning the spheres.
Christian Synthesis of Greek Works:
-after many centuries, this system was incorporated into Medieval Christianity. Heaven
was beyond the sphere of the fixed stars; God set the spheres in motion, and His angels
helped turn each sphere.
Heliocentric Model
-note that a few ancient Greeks had proposed a sun-centered universe, but their
arguments didn’t hold up to Ptolemy’s.
-in 1543, Nicholas Copernicus’ On the Revolutions of the Heavenly Bodies was
published. He proposed a sun-centered universe. Note that although this was a radical
change, he used many of the ancient geometrical devices that Ptolemy employed, the
details of which are beyond the scope of these notes (including epicycles). Still, the
Catholic Church didn’t get too upset at the time, as another man wrote in the introduction
to Copernicus’ book that the sun-centered theory was simply a mathematical device to
produce more accurate astronomical tables and wasn’t really the way the universe looked.
-then, in Italy, came Galileo Galilei. He got a hold of some Flemish glassworkers’ new
devices, modified them, and pointed them at the sky. These were the first refracting
telescopes (they used glass lenses). He quickly made some extraordinary discoveries,
including:
-way more stars than anyone had ever seen before
-the phases of Venus (this is really important in geometrically showing that Venus
must orbit the sun closer than earth’s orbit, supporting the Copernican theory)
-moons around Jupiter (surprise – not everything revolves around us, as Ptolemy
thought)
-big mountains and craters on the moon (another surprise – a heavenly body that
isn’t perfect?!) (Note that before then, the moon’s spotty appearance was
explained away as changes in the density of the ether between earth and the
moon)
-spots on the sun (uh oh, the sun isn’t perfect either)
-the sun rotates on its axis every few weeks
-a bump around the center of Saturn (determined after Galileo’s death to be
rings)
-Galileo, a devout Catholic, tried to convince Catholic officials that the Copernican
system was clearly correct and they should adopt it to prevent looking foolish. The
Catholic Church responded by beginning secret files on him. He was also warned to
watch his step. (Note that at the time, the heliocentric model was considered to be
heretical, as it did not comply with various Biblical teachings.)
-Galileo later published a book in which he stages a mock debate between advocates of
the geocentric and heliocentric systems. He, of course, has the heliocentric person win.
Pope Urban VIII was convinced by colleagues that the Pope himself was the model for
the geocentric advocate, and therefore Galileo was really making fun of him. The Pope
forced Galileo to recant publicly his beliefs and he spent the rest of his life under house
arrest.
-other important people:
-Tycho Brahe, who receives only a passing mention in the text, is actually considered to
be one of the greatest naked-eye observers of the modern era. He built a great
observatory called Uraniborg on the island of Hven in Denmark. He came up with the
Tychonic System, a very clever model of the universe that, unfortunately, we don’t have
time to discuss here. He did, however, observe two key events:
-a supernova, which, using very careful observations, he determined occurred in
the sphere of the supposedly unchanging stars, not in the atmosphere of earth
-a comet, which, again, using very carefully observations, he determined must be
crashing through the crystalline planetary spheres. This led him to a huge
discovery: THERE WERE NO SPHERES.
-Johannes Kepler took up Brahe’s work when he died. Kepler came up with 3 extremely
important laws, but the key concept we will cover here is: the planets don’t move in
perfect circles. Their orbits are actually elliptical (though only slightly elliptical). This
proved to be a big help to making astronomical tables more accurate.
-the last person I’ll mention is Isaac Newton, who isn’t even mentioned in your book,
which makes me very sad , considering he may be one of the smartest people who ever
lived. Just to wrap it up, Newton made almost all of his discoveries during 9 months in
1666 when he had to leave Cambridge because it was closed due to a plague outbreak.
During that time (and through developments later in his life), he came up with: 1. his
theory on optics (including that white light is made up of all the colours); 2. his theory
on universal gravitation (that all objects with mass are attracted to all other objects with
mass in the universe, and that this force acts over empty space – no ether); and 3. calculus
(although a guy in Europe named Leibniz also came up with this around the same time,
which made Newton very angry). Newton destroyed any last beliefs anyone had in the
geocentric theory. By the way, Newton spent much of his life studying Biblical
chronology and alchemy.
-then lots of other stuff happened, but unfortunately, that is beyond the scope of these
notes, so when you get to university, go take some history of science and astronomy
classes!!!!
Section 1.2: Discovery through Technology
-before the invention of telescopes, people were building tools to help them better
understand the cosmos. Examples include:
-the sundial: used to tell time
-the quadrant: used to measure a star’s height above the horizon
-the astrolabe: used to make accurate star charts
-the cross-staff: used to measure the angle between the moon and any given star
-then, the telescope was invented. First, people used refracting telescopes (first used to
look at the stars by Galileo Galilei around 1607), which are made with lenses. Better and
better lenses and telescopes were built.
-later, reflecting telescopes, which use mirrors, were built (the first working one was built
by Isaac Newton in the late 1600s to early 1700s).
-currently, we use huge telescopes on earth and in space. Some of the telescopes use the
visual part of the spectrum, but others are radio and X-ray telescopes.
Important Unit Definitions:
-AU (astronomical unit): the average distance between the earth and the sun
-this equals about 150 million km, or about 93 million miles for you Imperial
folks
-this unit is handy for measuring distances in our own solar system.
-so, earth is 1 AU from the sun; Uranus is about 18 AU from the sun; Pluto is
about 39 AU from the sun.
-light-year: the distance light travels in one year
-this equals about 9.5 trillion km (as light moves at 300 000 km per second).
-we use light-years when talking about interstellar distances (the distances
between stars).
-the nearest star to us (besides the sun) is Proxima Centauri. It is just over 4 lightyears away.
-note that when you look at an object in space, you are not seeing it as it presently looks.
An example is the sun: it takes light about 8 minutes to travel from the sun to the earth,
so when you see the sun (of course you would never look at the sun directly!!), you are
seeing it as it appeared 8 minutes ago.
-If you look through a powerful telescope and see Pluto, you are seeing it as it looked 5
hours ago.
-If you look at Proxima Centauri, you will see it as it appeared 4 years ago.
-If you look at the Andromeda Galaxy, you are seeing it as it looked 2 million years ago.
-If you look at some distant galaxies through the Hubble Space telescope, you are seeing
them as they appeared 12 billion years ago.
So: looking into space = looking into the past. Also, some of the stars you see in the sky
may have died a long time ago, and other stars that have just been born won’t be visible
to us for years.
Section 1.3: The Distribution of Matter in Space
What is a star?
-a star is a hot glowing ball of gas that gives off lots of light. It is mainly composed of
hydrogen.
-there are billions of billions of stars. Some stars are much bigger than others; some are
much denser than others. Colours vary; blue = hot while red = cool.
-our sun falls into a category of stars called main sequence stars. 90% of all stars fit into
this group.
Star Life Cycle
-stars are born in nebulae, regions which contain lots of gases and dust. Nebulae contain
about 75% hydrogen and 23% helium; the rest is oxygen, nitrogen, carbon, and silicate
dust.
-gravity can cause a small section of the nebula to collapse into a small, rotating cloud.
More material gets drawn in and its temperature rises. If the temperature rises enough, it
will glow; this is called a protostar. The core of the protostar continues to get hotter.
Once the core temperature reaches 10 million degrees Celsius, fusion from hydrogen to
helium starts, releasing lots of energy. A star has been born 
-the star may be a main sequence star, like our sun, or else, more rarely, be massive.
Both types of stars are stable for millions to billions of years, changing hydrogen to
helium for fuel.
-however, the fuel eventually runs out. When hydrogen runs out, the star shrinks, heating
the helium so it fuses to form carbon, and then other elements. More nuclear reactions
then case the outer layers of the star to expand, turning the star into a red giant, or, in the
case of a massive star, a red supergiant. (Our Sun will turn into a red giant in about 5
billion years, and will likely be so big it will swallow Mercury, Venus, Earth, and Mars.)
-eventually, the fusion reactions stop. For a star like our Sun, this occurs when the core
temperature drops too low to keep the reactions going. The star slowly collapses,
becoming a white dwarf, no larger than the size of Earth. Then, it fades into a cold, dark
black dwarf. However, it may take billions of years to cool from a white dwarf to black
dwarf stage, so we don’t know if any black dwarfs exist in the universe yet.
-however, in a massive star, the fusion reaction stops when the star runs out of fuel.
Because it is so massive, gravity causes the star’s core to collapse rapidly. This ends
suddenly with an outgoing shock wave. This causes the outer part of the star to explode
violently; this is called a supernova. They light up entire galaxies and in the past have
appeared as sudden very bright stars in our sky which quickly fade. If the star is not
totally destroyed by the explosion, the leftover core can become one of two things:
-a neutron star, a rapidly spinning, extremely dense object no bigger than 30 km
wide
-a black hole, where gravity is so strong that not even light can escape.
Star Groups
-constellations are groupings of stars we see as patterns. Officially, there are 88
constellations.
-many unofficial star groupings are called asterisms. These include the Big Dipper,
which is in the constellation Ursa Major (the great bear).
Galaxies
-a galaxy is a grouping of millions or billions of stars, gas, and dust that is held together
by gravity.
-our galaxy is called the Milky Way. It is classified as a spiral galaxy. It has between
100 billion to 200 billion stars.
-the other two types of galaxies are called elliptical and irregular.
-there may be a billion billion galaxies in the universe.
Section 1.4: Our Solar Neighbourhood
-according to the protoplanet hypothesis model, a solar system is born in three steps:
1. A cloud of gas and dust in space begins to swirl.
2. Most of the material (over 90%) accumulates in the centre, forming the sun.
3. The remaining material accumulates in smaller clumps circling the centre.
These form planets.
-Our Sun
-110 times wider than earth
-1 000 000 earths could fit inside it.
-the temperature at the surface of the sun is 5500 C, whereas the core
temperature is 15 000 000 C.
-the sun releases charged particles that flow out in all directions. This is called
the solar wind, and its average speed is 400 km/s. Earth’s magnetic field protects
us from the solar wind.
-Check out www.spaceweather.com for today’s solar weather forecast!
-The Planets
-the planets are usually divided into the inner planets (Mercury, Venus, Earth,
and Mars), which are smaller and terrestrial, and the outer planets (Jupiter, Saturn,
Uranus, Neptune, Pluto), which, with the exception of Pluto, are large, gaseous planets.
(Pluto is the exception; it is terrestrial and is quite small.)
Other bodies in our Solar System:
-between Mars and Jupiter is the asteroid belt. The asteroids in this belt orbit the sun.
Asteroids range in size from a few meters to several hundred kilometers across. The
largest is Ceres, which is over 100 km wide.
-comets, also known as dirty snowballs, are made of dust and ice. Their long tails and
bright glow only occur when they get near the sun; this is because the sun heats up the
comet causing gases to be released, which the solar wind then pushes out into a tail.
Comets spend most of their time slowly orbiting the outer reaches of the solar system
(many beyond Pluto). Some comets orbit the sun regularly, such as Halley’s comet,
which is visible from earth every 76 years.
-pieces of rock flying through space with no particular path are called meteoroids. They
can be as small as dust or as big as a car.
-when earth’s gravity pulls one in, the heat of atmospheric friction causes it to give off
light. This is called a meteor, or shooting star. If a piece of a meteor lasts long enough
to hit Earth’s surface, it is called a meteorite. Some meteor showers occur regularly,
such as the Perseids and the Leonids.
Tracking Objects in the Solar System
-the paths of objects in the solar system are elliptical. Since we understand elliptical
geometry, we can predict where an object has been in the past and where it will be in the
future.
Section 1.5: Describing the Position of Objects in Space
-two measurements are necessary to describe the position of an object in our night sky:
1. azimuth: where an object is in relation to a compass, e.g. north, south, east,
or west. 0 = north, 90 = east, 180 = south, and 270 = west.
2. altitude: how far an object is above the horizon; that is, how high in the sky
it is. If it is on the horizon, it is at 0; if it is directly overhead, it is at 90.
The point in the sky directly over your head is called the zenith.
Determining the Position of Objects in Space
-recall that planet comes from the Greek word meaning wanderer, as planets wander
against the apparently fixed background of the stars. (Note: you can only see real stars
move relative to one another over a period of many thousands of years.)
-the path that the sun takes across the sky is called the ecliptic.
-the celestial sphere is the name given to the very large imaginary sphere of sky
surrounding the earth.
-the celestial equator is the imaginary line around that sphere of sky directly above the
earth’s equator. The ecliptic crosses the celestial equator at the vernal (spring) and
autumnal (fall) equinoxes. The sun’s most northerly position on the ecliptic is the
summer solstice; the sun’s most southerly position on the ecliptic is the winter solstice.
(My thanks to Christina Willson for creating and sharing this
document.)