Sunday, April 15, 2012

Astronomy Study Guide

Celestial Sphere - an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the celestial equator and the celestial poles. The celestial sphere is a very practical tool for positional astronomy.

North Star – Star closest to the Celestial North Pole

The north and south celestial poles are the two imaginary points in the sky where the Earth's axis of rotation, indefinitely extended, intersects the imaginary rotating sphere of stars called the celestial sphere. The north and south celestial poles appear directly overhead to an observer at the Earth's North Pole and South Pole respectively.

Solar Day - The length of time which elapses between the Sun reaching its highest point in the sky two consecutive times. This is what is usually simply called "the" day.

year - the orbital period of the Earth moving around the Sun.

Celestial Equator - a projection of the terrestrial equator out into space.[1] As a result of the Earth's axial tilt, the celestial equator is inclined by 23.4° with respect to the ecliptic plane.

Constellation - totally imaginary things that poets, farmers and astronomers have made up over the past 6,000 years (and probably even more!). The real purpose for the constellations is to help us tell which stars are which, nothing more. On a really dark night, you can see about 1000 to 1500 stars. Trying to tell which is which is hard. The constellations help by breaking up the sky into more manageable bits. They are used as mnemonics, or memory aids.

Circumpolar Stars - a star that, as viewed from a given latitude on Earth, never sets (that is, never disappears below the horizon), due to its proximity to one of the celestial poles. Circumpolar stars are therefore visible (from said location) for the entire night on every night of the year.

All circumpolar stars are within the circumpolar circle. This was in fact the original meaning of "Arctic Circle", before the current geographical meaning

Ecliptic - is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun.

The Tropic of Cancer and Tropic of Capricorn respectively mark the northernmost and southernmost latitudes at which the sun may be seen directly overhead (at the June solstice and December solstice respectively).

Arctic Circle - marks the southern extremity of the polar day (24-hour sunlit day, often referred to as the "midnight sun") and polar night (24-hour sunless night). North of the Arctic Circle, the sun is above the horizon for 24 continuous hours at least once per year and below the horizon for 24 continuous hours at least once per year. On the Arctic Circle those events occur, in principle, exactly once per year, at the June and December solstices, respectively.

Antarctic Circle - marks the northernmost latitude (in the Southern Hemisphere) at which the sun can remain continuously above or below the horizon for 24 hours.

Precession - a change in the orientation of the rotation axis of a rotating body. Earth has a 26,000 year change in tilt.

Zodiac - The zodiac (Greek: ζῳδιακός, zōdiakos) is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year.

Saros - a period of 223 synodic months (approximately 6585.3213 days, or nearly 18 years 11 days), that can be used to predict eclipses of the Sun and Moon. One saros after an eclipse, the Sun, Earth, and Moon return to approximately the same relative geometry, and a nearly identical eclipse will occur, in what is referred to as an eclipse cycle. A sar is one half of a saros.

Prograde – Apparent forward motion of an object against the celestial sphere. east to west motion.

Retrograde - Apparent backward motion of an object against the celestial sphere. west to east motion.

ellipse – the orbit of a planet, two pins and string, draw a circle with the string, will form an ellipse. A circle is a special case of an ellipse with both foci in the same location, never found in nature. The sun is in one foci.

focus, foci - the center/centers of an ellipse/circle.

Period - the time taken for a given object to make one complete orbit about another object.

Uniform Motion – an object in motion with no outside forces acting on it.

Speed – distance traveled in a given amount of time.

Acceleration – The change in speed of an object from a given force.

What is science? the systematic observation of natural events and conditions in order to discover facts about them and to formulate laws and principles based on these facts. 2. the organized body of knowledge that is derived from such observations and that can be verified or tested by further investigation.

What is Empiricism? Empiricism is a theory of knowledge that asserts that knowledge comes only or primarily via sensory experience.

How do people come to accept things in science? Kicking and screaming denials until the level of proof becomes so overwhelming that anyone who denies the facts is ridiculed by all their friends.

Who came up with the Science classification system we use today? The Greeks.

What is the role of experiment in science? Testing Hypothesis.

Be familiar with cave man astronomy.

Describe the basic motion of the stars - once every 24 hours.

Sun rises 3 minutes 56 seconds later than the stars everyday.

Moon rises 50 minutes later than the Stars everyday.

Everything rises in the east and set in the west.

Sun and planets mostly go along the ecliptic, where the zodiac is.

Sun seems to move through the zodiac all year long.

What causes the seasons? Tilt of earth 23.5 degrees.

Why is summer hotter than winter. Sun is higher in the sky and sunlight goes though less atmosphere.

What are the causes of eclipses?

What causes phases of the moon? Angle between earth, sun and moon causes the shadow on the sun to vary over the orbit of the moon around the earth

Solar Eclipse - The moon blocking the sun, a total eclipse is where the moon's shadow crosses the earth, a partial is observed from a certain distance from the path of the moon's shadow across the earth.

Lunar Eclipse – Earth's shadow crossing some portion or all of the Moon.

Waxing – As the moon approaches full.

Waning – As the moon new.

Difference between Geocentric and Heliocentric Universe – Geocentric is Earth centered, Heliocentric is sun centered. We believe in Star centered stellar systems.

What did each of the following contribute?

The Greeks – science, classification system,

Copernicus – Sun was center of the solar system.

Tycho Brahe -

Kepler -

Galileo – telescopes, thermo-scopes, kinematics, wrote popular books presenting the view that the sun was center of solar system, which lead to his house arrest by the church.

Newton – calculus, laws of motion, law of universal gravitation, alchemist, reflecting telescope, theory of color, occult studies

What calender do we use today? Gregorian

How is it different than the previous Julian calendar? Julian calendar numbered each day from start of year, had a leap year every 4 years.

Is there a leap year every 4 years in the Gregorian Calendar? Leap year every 4 years, unless it is divisible by 100, unless it is divisible by 400.

3 Major types of calendar?

Solar -

Lunar -

Lunisolar -

Metonic cycle is where the lunar and solar calendars line up every 19 years. Jewish calendar is one of them.

What are Kepler's three laws?

  1.     The orbit of     every planet is an     ellipse with the     Sun at one of the two foci.        
  2.     A line     joining a planet and the Sun sweeps out equal areas     during equal intervals of time.[1]        
  3. The square     of the orbital     period of a planet is directly proportional     to the cube     of the semi-major     axis of its orbit.     

Why are Kepler's laws useful? Tell us a lot about planetary motion.

What did Galileo do to make the church mad at him? Wrote a satirical book presenting the view that the sun was the center of the solar system.

What did Galileo discover? Sunspots, rings around Saturn, venus has phases, moons around jupiter.

What are Newton's three laws?

  1.     Every     object in a state of uniform motion, or at rest, tends to remain in     that state of motion unless an external force is applied to it, or     at rest.
  2.     Total     force on an object is equal to the product of the object's mass     times its acceleration. F=ma << science.
  3.     For     every force that an object exerts on a second object, there is an     equal and opposite force exerted by the second object on the first.

What is Newton's Universal Law of Gravitation?

F = (G M M )/d^2

How did the Greeks laws of motion differ from Newton's ideas?
    Greeks thought that the natural state is rest and that force is needed for motion. 

Newton incorporated both rest and motion into his ideas and said that force just applies acceleration to an object.

Planets order from Mercury to Neptune – m v e ma j s u n p

Planets in size from small to big – p m v ma e u n s j

Mars and Venus have no Magnetic field.

Yearly differences caused by orbit around the sun.

Daily differences rotation of earth.

Monthly differences

Comets have tails, asteroids don't

What are the planets relative densities?

RankNameDensity (kg pr. cubic meter)
1Earth         5515
2Mercury         5427
3Venus         5243
4 Mars         3933
5 Moon         3350
6 Pluto         1750
7 Neptune         1638
8 Sun         1408
9 Jupiter         1326
10 Uranus         1270
11 Saturn         687

Source: NASA

What are the special characteristics of each planet?

mercury - smallest of the terrestrial planets.
the fastest orbiting planet in our solar system.
rotation axis is aligned along its orbital pole.

venus - weather patterns
to the naked eye, Venus is the brightest star like object in the sky.
it is transparent to visible light, but nearly completely blocks infrared sometimes called "heat radiation".

earth - life-sustaining
abundance of water
the largest of the terrestrial planets in the Solar System in diameter, mass and density

mars - has a volcano that is three times higher than Mount Everest
it is the planet that we most often relate extraterrestrial life to
home to one of the longest (more than 4,000 km (2500 miles long)) canyon systems in the solar system called Valles Marineris ("Mariner Valley").

jupiter - its immense size
the Great Red Spot.
has the most moons of any planet in the solar system

saturn - Great White Spot
magnificent ring system.
it is the least dense of all the planets.

uranus - the only planet that rotates on its side.
discovered by accident in 1781 by William Herschel.
there is absolutely no detail in the cloud cover

neptune - Great Dark Spot
extremely violent hurricanes
Neptune is never visible with the naked eye.

pluto - the only "planet" not yet explored by space probes
higher eccentricity, higher inclination orbit than any other planet
the farthest planet from the Sun

Earth - Water, magnetic field, life

What moons do each planet have?

All planets except Mercury and Venus have at least one moon. Saturn has the greatest number of moons—18. In 1995, the Hubble Space Telescope detected what appeared to be four additional moons of Saturn; however, that discovery has yet to be confirmed.

PlanetNumber of MoonsNames of Moons
Earth1The Moon (sometimes called Luna)
Mars2Phobos, Deimos

*Several other satellites have been reported but not confirmed.

Jupiter16*Metis, Adrastea, Amalthea, Thebe, Io, Europa, Ganymede, Callisto, Leda, Himalia, Lysithia, Elara, Ananke, Carme, Pasiphae, Sinope
Saturn18*Atlas, 1981S13 (unnamed as yet), Prometheus, Pandora, Epimetheus, Janus, Mimas, Enceladus, Ththys, Telesto, Calypso, Dione, Helene, Rhea, Titan, Hyperion, Iapetus, Phoebe
Uranus15Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, Puck, Miranda, Ariel, Umbriel, Titania, Oberon
Neptune8Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, Triton, Nereid

Sources: Famighetti, Robert, ed. World Almanac and Book of Facts 1996, pp. 279-80; The Universal Almanac 1992, pp. 17-22.
Source: UXL Science Fact Finder, ©1998 Gale Cengage. All Rights Reserved.

 What are comets?  Kuiper belt objects that are thrown into the inner planets by the large outer planets, mainly Jupiter.   They are composed of ice and rock and dust.  As they approach the sun they are heated and release jets of water vapor and dust.  This dust and water vapor is pushed away by the sun’s solar wind creating large tails that can be stunning in size.  The ancients believed that seeing a comet in the sky was a bad omen.

Comets come from two places in the Solar System: the Oort Cloud and the Kuiper Belt.



meteor showers?  These are remnants of ancient comets.  Over a long time the debris from a comet will spread out along it’s orbit.  As the earth intersects the orbit of these objects there is an increase in the number of meteors you see.

What is the Oort Cloud?  The Oort Cloud is a spherical halo of comets surrounding the Solar System at a distance of around 50,000 Astronomical Units.

Kuiper Belt Object?  The Kuiper Belt is a ring of icy objects beyond the orbit of Neptune (30-100 AU). It lies (more or less) in the plane of the solar system and is a reservoir for the short period comets that we see.    These objects are most likely pulled from the Oort cloud and down into the plane of the solar system by the large outer planets.

How did the solar system begin?  

Condensation model.  

Large cloud of dust and gas.  The dust particles began clumping together.  The clumps formed larger clumps.  These larger clumps began to collide and combine with each other.   The cause to start this event is unknown.   Any sort of compression wave might have been enough to push things together.  Could be a spontaneous event.

What is a protosun?  A object that has accumulated enough matter to be a star, but the nuclear process that powers stars is still starting up.

What is differentiation?  The planets got big enough to retain heat and have liquid interiors. The heavier materials like iron and nickel sank to the planet cores while the lighter materials like silicates and gases rose toward the surface, in a process called differentiation.

What are Jovian and terrestrial planets?  Jovian planets are large gas giants in the outer solar system.  The inner planets are rocky solid objects.   One theory is that they were beyond a stellar frost line where H2O and other gases could condensate into fluids or solids.    Inside this frost line the planets were unable to capture as much of this material and formed smaller, denser planets.

What is a planetismal?  When dust and ice particles in a protoplanetary disc merge, the large clumps collide into even larger bodies called planetesimals. When planetesimals begin to stretch a few miles across, they muster enough of a gravitational field to gather round even more planetesimals and form a young planet called a protoplanet.

What is a protoplanet?  Protoplanets are large planetary embryos that originate within protoplanetary discs and have undergone internal melting to produce differentiated interiors. They are believed to form out of kilometer-sized planetesimals that attract each other gravitationally and collide. According to planet-formation theory, protoplanets perturb each other's orbits slightly and thus collide to gradually form the dominant planets.

What is a planet?  the decision last August by the International Astronomical Union (IAU), astronomers' main professional society, to define a planet as an object that orbits a star, is large enough to have settled into a round shape and, crucially, "has cleared the neighborhood around its orbit."

What is albedo?  Reflected light, 1.0 reflects 100%, 0.0 reflects none.

What is the green house effect, and how does it run away?

Some gasses hold heat in better than other gasses, such as CO2.  If you get enough of that gas then it will hold in more and more heat, vaporizing any lighter gasses and causing them to escape from the planet.   Eventually the entire atmosphere will consist of the green house gases at high pressures and be locked into a high temperature.   This heat will be spread evenly around the entire planet by convection cells.   Venus is an example of such a planet.

What is the Coriolis effect?  As a planet rotates it exerts a small apparent force on anything moving across the planets surface.   This is the same apparent force that would cause a ball to appear to curve opposite the direction of movement if you were rolling it back and forth on a merry go round.

What are the layers of the atmosphere?  

the space between earth’s magnetic field and free space.
The earths magnetic field in space.  Blown out of shape by the solar wind.
the rest of the way out.  Gets thinner and thinner forever.
upto 600km out.
upto 95 km.  temperature drops with increase in altitude because the low density doesn’t allow heating by ultraviolet light.  
next layer up.  50 km high.  19% of atmosphere, very little water vapor.  Temperature increases with altitude. This prevents "convection" since there is no upward vertical movement of the gases and is the reason for the 'anvil-shaped' tops of cumulonimbus clouds. These anvils occur at the tropopause.
about 15 km high.  layer closest to the ground. Densest layer.  Temperate drops as you go up.  Most weather here.

What is the aurora?  The aurora is caused by charged particles coming down in the gaps of the magnetic field at the poles and spreading out into the upper atmosphere.  This creates spectacular light shows.

What is energy?  The potential to do work.

What are the two forms of Energy?  Potential and Kinetic.

What is escape velocity?
The speed something has to go in order to move out of the gravitational influence of another body.

What effect does escape velocity have on planets?  
Lighter gases move faster than heavier gases at the same temperature.  if this extra speed is greater than the escape velocity of the planet, then the lighter gasses will tend to escape more easily than the heavier gasses.  This leads to the loss of light gasses such as helium and hydrogen from the atmosphere and the retention of the heavier gasses.
Changes the composition of the atmosphere.  Lighter molecules stay escape, because they are moving faster.  Heavier molecules tend to stay because they are moving slower.

Explain tidal forces.  
Tidal forces are created by a gravitational gradient.  The further from an object, the less   The force on one side of an object is greater than the force on the other side of the object, causing that side to be pulled out.

Why are tidal forces so important in Astronomy?
Many of the moons of larger planets are heated internally by tidal forces from their primary and other moons orbiting the planet.

Stars are classified by their  spectra ( the bands of light they emit) and their temperature.

What are their stellar classes?  

< - hotter
Oh Be A Fine Girl, Kiss Me
                          cooler - >

apparent magnitude (m) of a celestial body is a measure of its brightness as seen by an observer on Earth, normalized to the value it would have in the absence of the atmosphere. The brighter the object appears, the lower the value of its magnitude.

What is a wave?
a disturbance that travels through a medium from one location to another location.  This transports energy, not matter.
The speed of a wave is = wavelength * frequency

The distance from one fixed point on a wave to the same point on the next wave.

wavelength = speed of the wave / frequency

How long does it take a wave to pass a fixed point.  The time it takes to complete a cycle is the period.


How many waves pass a fixed point in one second.


What is a photon?   A particle of light.

What is light?
Light is the part of the electromagnetic spectrum visible to the naked human eye.  It is one tiny part of a vast spectrum of electromagnetic radiation.

Why is the study of light important?  The study of visible light led to the discovery of the invisible areas next to the visible light spectrum.  This lead to the discovery of infrared, ultraviolet and radio, which in turn lead to the discovery of the entire electromagnetic spectrum.

Draw a diagram of the electromagnetic spectrum.

        Less Energy.  Low frequency, long wavelength ->
Gamma | X-Ray | UV | Visible | IR | Microwave | Radio | ELF
<- high frequency, short wavelength.  More energy.

Describe the three types of spectrum?
Continuous Spectrum - light like the rainbow.  
Absorption Line Spectrum - dark lines on a continuous spectrum.  
Emission Line Spectrum - mostly dark, no continuity bright lines.

Why are they useful?  
If an electron jumps down from a higher level to a lower level, light with a specific energy (wavelength) will be emitted.  This light “fingerprint” can be used to determine what elements are present in a star far away and what conditions the elements are being subjected to.

What is Weins law?
The wavelength distribution of thermal radiation from a black body at any temperature has essentially the same shape as the distribution at any other temperature, except that each wavelength is displaced on the graph. Apart from an overall T3 multiplicative factor, the average thermal energy in each mode with frequency ν only depends on the ratio ν / T. Restated in terms of the wavelength λ = c / ν, the distributions at corresponding wavelengths are related, where corresponding wavelengths are at locations proportional to 1 / T. Blackbody radiation approximates to Wien's law at high frequencies.

What is the Stephan Boltzman law?  
The total energy radiated per unit surface area of a black body per unit time (also known as the black-body irradiance or emissive power), j*, is directly proportional to the fourth power of the black body's thermodynamic temperature T (also called absolute temperature):  

What is the doppler effect?  
The perceived change in frequency of a wave source based on the speed and direction of the wave source and the object perceiving the wave.  Waves appear higher pitched when moving towards each other and lower pitched when moving away from each other.

What are the two kinds of telescopes?  Reflector and refractors.

What are the subtypes of reflector telescope?
Newtonian and Dobson, hybrid (Schmidt-Cassegrain and Cassegrain),

What kind of telescope is the least expensive?
Small refracting telescopes.

What kind of equipment do astronomers typically put on a telescope to observe the stars?  
Motors to track the stars, spectrometers to analyse the stars, light sensors to measure absolute brightness, CCDs and cameras to take pictures of the stars.

What is the advantage of larger telescopes?  
The larger the opening the more photons enters the device.  The more photons means that you can build up an image more rapidly, see objects dimmer and further away than you can with a telescope that has a smaller opening.  Sharper pictures as well.

What is the advantage of a space telescope?  No atmosphere. 

What are sunspots?  

temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature. Like magnets, they also have two poles. Although they are at temperatures of roughly 3000–4500 K (2727–4227 °C), the contrast with the surrounding material at about 5,780 K leaves them clearly visible as dark spots, as the intensity of a heated black body (closely approximated by the photosphere) is a function of temperature to the fourth power. If the sunspot were isolated from the surrounding photosphere it would be brighter than an electric arc. Sunspots expand and contract as they move across the surface of the Sun and can be as large as 80,000 kilometers (50,000 mi) in diameter, making the larger ones visible from Earth without the aid of a telescope.[1] They may also travel at relative speeds ("proper motions") of a few hundred m/s when they first emerge onto the solar photosphere.

Solar flares?

A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy[1] (about a sixth of the total energy output of the Sun each second). The flare ejects clouds of electrons, ions, and atoms through the corona into space.

granules?  on the photosphere of the Sun are caused by convection currents (thermal columns, Bénard cells) of plasma within the Sun's convective zone. The grainy appearance of the solar photosphere is produced by the tops of these convective cells and is called granulation.


a large, bright feature extending outward from the Sun's surface, often in a loop shape. Prominences are anchored to the Sun's surface in the photosphere, and extend outwards into the Sun's corona. While the corona consists of extremely hot ionized gases, known as plasma, which do not emit much visible light, prominences contain much cooler plasma, similar in composition to that of the chromosphere. A prominence forms over timescales of about a day, and stable prominences may persist in the corona for several months. Some prominences break apart and give rise to coronal mass ejections.

solar wind?  a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time. These particles can escape the Sun's gravity because of their high kinetic energy and the high temperature of the corona.

The solar wind creates the heliosphere, a vast bubble in the interstellar medium that surrounds the Solar System. Other phenomena include geomagnetic storms that can knock out power grids on Earth, the aurorae (northern and southern lights), and the plasma tails of comets that always point away from the Sun.

photosphere?  the visible surface of the Sun that we are most familiar with. Since the Sun is a ball of gas, this is not a solid surface but is actually a layer about 100 km thick (very, very, thin compared to the 700,000 km radius of the Sun). When we look at the center of the disk of the Sun we look straight in and see somewhat hotter and brighter regions.

chromosphere?  (literally, "color sphere") is a thin layer of the Sun's atmosphere just above the photosphere, roughly 2,000 kilometers deep.

Although thin, its density increases over almost seven orders of magnitude (five million times) from a low of 1.0 × 10−11 kg/m3 (1.0 × 10−14 g/cm3) at its boundary with the solar transition region, and increasing to a high of 2.0 × 10−4 kg/m3 (2.0 × 10−7 g/cm3) where it merges into the photosphere.[1] See Figure 1. Skylab's solar atmosphere results chart for details of how its temperature and density vary with height.

corona?  One of the most puzzling features of the Sun is what has been dubbed "the solar corona problem." There is a region around the Sun, extending more than one million kilometers from its surface, where the temperature can reach two million degrees. This region, called the solar corona, is where the solar wind originates. The corona has been found to emit X-ray radiation (the corona is a plasma; at temperatures greater than a million degrees a plasma will radiate a lot of X-rays). 

The corona can be seen only during solar eclipses, when the main radiation from the Sun's surface is blocked by the passage of the Moon or with special instruments.

The problem is, no one can really explain how this corona exists. Even if the temperature in the core of the Sun does reach 15 million degrees, it drops to a mere 5000 degrees at the surface. The temperature should be even lower farther away from the Sun, but the temperature of the corona is measured at more than a million degrees. This incredibly hot temperature requires a permanent heating mechanism, or the plasma would cool down in about an hour. There are many mechanisms which could heat some gas above the surface of the Sun, but none of those mechanisms could account for the large rate of heating necessary to heat the corona to these temperatures. This phenomenon remained a mystery for more than 50 years.

 What happens to the temperature in the atmosphere of the Sun?

The surface of the Sun, the part that we can see, is known as the photosphere. This is the region where light from inside the Sun can finally reach space. The temperature of the photosphere is approximately 6000 K, and glows with white light. But the Sun doesn’t end there. Directly above the photosphere is where the Sun’s atmosphere, and it stretches for several hundred thousand kilometers. Let’s take a look at the atmosphere of the Sun.

The first region in the atmosphere of the Sun is the called the temperature minimum, and it sits about 500 km above the photosphere, and has a temperature of about 4,000K. In this part of the Sun, it’s cool enough that simple molecules like water and carbon monoxide can be detected.

The next layer in the Sun’s atmosphere is known as the chromosphere. It’s only about 10,000 km thick (about the diameter of the Earth), but it quickly rises in temperature as it rises in altitude. At the top of the chromosphere, temperatures can reach 20,000 K. The chromosphere is invisible without special equipment that use narrow-band optical filters to see the region. Gigantic solar prominences can rise through the chromosphere reaching altitudes of 150,000 km.

Above the chromosphere is known as the transition region. Below this region, gravity is the dominant force that shapes the features. Above the transition region, temperatures rise quickly because helium becomes fully ionized. Once ionized, helium holds onto heat.

The next layer is the corona, and it extends outwards from the Sun for millions of kilometers into space. You can see the corona during a total solar eclipse, when the disk of the Sun is blocked by the Moon. The temperature of the corona is about 200 times hotter than the surface of the Sun. While the photosphere is only 6,000 K, the corona can reach 1-3 million degrees K. Scientists still aren’t sure why the temperature of the corona is so high.

The uppermost part of the Sun’s atmosphere is the heliosphere. This is the bubble of space filled with the solar wind that extends out about 20 astronomical units (1 AU is the distance from the Earth to the Sun). It is eventually slowed and stopped by the interstellar medium.

What are sunspot cycles?  11 year period of periodic variation in the average number of sunspots.  During periods were there are few sun spots the solar radiation from the sun seems to be minimized.  The  Little Ice Age corresponded with the Maunder minimum of 1645 - 1715.

What kinds of effects on the Sun can have an effect on the Earth? Solar flares and knock out our electrical systems and cause large light displays in our atmospheres called the northern lights.

What are the characteristics of the stars?  Emit light from the fusion of hydrogen and other elements.

What is an H-R diagram?   Sequence diagram of stars

What does it mean?  Stars fit into the diagram in certain spots depending on their size and age.

Describe the life cycle of the stars?  Stars form from dust, begin burning hydrogen fusion, and slide into the main sequence.   Depending on size they slide down and to the left until they expand and blow off their outer shells and become white dwarfs or neutron stars.  If they are massive they will burn out their fuel suppy, collapse into themselves and form a super nova or nova.  This forms large nebula which are nurseries for other stars to form.

Big dust cloud
shrinks into multiple stars
Big stars form first
Smaller stars form second

proto stars -> star begins burning hydrogen.

How is it different for stars of different mass?

Low mass - > blows off mass, becomes a white dwarf
a trillion years.

medium mass -> main sequence
100 billion years.

High mass moves up to a giant.  They burn up and either become novas or black holes.

Why are binary stars usedful to astronomers?  Binary stars are very useful to astronomers because it allows us to measure the mass of the stars in the system (by Kepler's laws). If the mass of the compact object turns out to be more than the critical mass mentioned above, then one can be sure that it is a black hole. So that is how black holes are discovered.

What are the different kinds of binary star?  Detached binaries are binary stars where each component is within its Roche lobe, i.e. the area where the gravitational pull of the star itself is larger than that of the other component. The stars have no major effect on each other, and essentially evolve separately. Most binaries belong to this class.

Semidetached binary stars are binary stars where one of the components fills the binary star's Roche lobe and the other does not. Gas from the surface of the Roche-lobe-filling component (donor) is transferred to the other, accreting star. The mass transfer dominates the evolution of the system. In many cases, the inflowing gas forms an accretion disc around the accretor.

A contact binary is a type of binary star in which both components of the binary fill their Roche lobes. The uppermost part of the stellar atmospheres forms a common envelope that surrounds both stars. As the friction of the envelope brakes the orbital motion, the stars may eventually merge.

What are the classes of binary stars?

How can being a member of a binary star system change a stars evolution?  Because the size of a star changes as it ages, when it begins to expand matter can be pulled into the other star.

What are the methods we talked about that can be used to tell distances to stars?

Paralax, red shift.

What holds stars together?  Gravity.  football Rho G h.

What keeps them from collapsing?  Pressures from inside.

What supplies fuel for a star?  Hydrogen, Helium and later carbon.

How long do stars live?  millions of years for large stars, billions of years for main sequence, trillions of years for white dwarfs.

What are the end products when stars die?  black dwarfs, neutron stars, black holes.

What are protostars?  Objects that are massive enough to become stars, but the fusion reactions have not began.

The main sequence?  How typical stars form and age.

dwarfs?  Small stars.

giants?   Large stars.

degenerate matter?  When matter is pushed together by forces that overcome first the electron repulusion and then later the nuclear forces.

The three end products of a star:
black holes?

neutron stars?

white dwarfs?

black dwarfs?

brown dwarfs?

planetary nebula?



What did Curtis and Shapely debate over?

The size and shape of the Universe and our galaxy.

Who won?

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