
                      *** ASTRONOMY ACTION ***


MEASURING TERMS:


     GREAT CIRCLE  The curve of intersection on the celestial sphere 
with a plane passing through its center.

     HOUR CIRCLES are circles passing through the celestial poles.

     THE ZENITH is the point directly overhead.

     CELESTIAL POLES are intersections of the celestial sphere with the 
earth's polar axis; the celestial sphere appears to rotate about these 
poles. Your latitude is equal to the altitude of the North Celestial 
Pole.

     THE CELESTIAL EQUATOR is the a great circle 90 degrees away 
from the celestial poles; it is the intersection of the celestial sphere 
with the plane of the earth's equator.

     THE ECLIPTIC is the apparent annual path of the sun on the 
celestial sphere; the apparent motion is due to the earth's revolution 
about the sun.

     ALTITUDE is the angular distance above or below the horizon, 
measured along a vertical circle, to an object.

     AZIMUTH is the angle along the celestial horizon, measured 
eastward from the north point, to the intersection of the celestial 
horizon with the vertical circle passing through the object.

     HOUR ANGLE is the angle measured westward along the celestial 
equator from the local meridian to the hour circle passing through 
the object, measured in time units.

     EPHEMERIS is a table giving the positions of celestial bodies at 
different times.

     DECLINATION is the angular distanced north (+) or south (-) of 
the celestial equator to some object, measured along an hour circle 
passing through that object. (It's like latitude).

     RIGHT ASCENSION  is a coordinate for measuring the east-west 
positions of celestial bodies; the angle measured eastward along the 
celestial equator from the vernal equinox to the hour circle passing 
through a body.

     NOTE: Right Ascension and Declination can be imagined by 
placing yourself inside a crystal globe of the earth and projecting 
the latitudes and longitudes  into the sky.

     SPEED OF LIGHT is 300,000 km/sec ( 3 X 108 meters/sec).

     LIGHT YEAR is the distance that light travels in one year.  It's 
billions and billions of kilometers!  (9 X 10 to the 12 km).

     DISTANCE TO THE MOON is about 300,000 km.  It takes light 
about 1 second to reach it.  Laser beams have been sent to the moon 
and reflected back from mirrors left there by the astronauts. This 
method enables us to calculate the distance to the moon to a few 
centimeters.

     DIAMETER OF THE EARTH is about 12,000 km. This was first 
measured by the Greek, Aritosthenese, by using the different angles 
made by the sun's shadow on the Summer Solstice in two different 
cities. 

     CIRCUMFERENCE OF THE EARTH is 40,000 km.  Light would make 
7.5 trips around the earth in one second.  This delay is noticed in 
radio communications.

     ASTRONOMICAL UNIT is the average distance from the earth to 
the sun, about 150 million kilometers. It takes light 8 minutes to 
reach us from the sun.
        The earth's orbit is an ellipse with the sun at one focus, hence 
the distance varies throughout the year.  (We, in the northern 
hemisphere, are closer in winter time!).

     PARALLAX is the angle (in seconds) subtended by one 
Astronomical Unit at the star's distance.

     THE PARSEC (parallel second of arc) is a method using the 
parallax of the spreading out rays to measure distance to stars. A 
parsec is the distance to a star whose parallax is 1 second of arc.  It 
is equal to 206,000 Astronomical Units, or 3 X 10 to the 15th 
kilometers.



MEASURING DEVICES:


     REFRACTING TELESCOPE uses lenses to collect light and magnify 
images.  The largest is 1-meter in diameter at Yerkes Observatory.  
Larger than this is impractical as the glass flexes due to its weight.

     REFLECTING TELESCOPE uses mirrors to collect light and magnify 
images.  The most important thing isn't as much to magnify as it is 
to collect more light to make the images brighter. The largest are the 
5-meter at Polamar and the 6-meter in the USSR.

     MULTIPLE MIRROR TELESCOPES are now being built.  UCSC will 
sponsor the 10-meter, and a 15-meter is being planned. Several 
mirrors are electronically moved to focus to the correct place.

     RADIO TELESCOPES use parabolic dish antennae to pick up the 
long wave radiation from the galaxies.  Shorter waves are visible 
light, and infra-red.  Famous are the great movable 100- meter dish 
at Jodrell Bank in the Mother Country, and the huge, 300-meter 
stationary hole-in-the-ground dish at Arecebo, South America.


     SPECTROSCOPES using prisms or diffraction gratings split the 
starlight into line spectra.  The spectral lines enable us to identify 
the elements in the stars or nebula, (by comparing them to spectra 
of known elements), and to tell what percent the elements are 
present, (by their intensities). Furthermore, the shifting of the lines 
enable us to measure the speed of stars and their rates of rotation.  
Ah Yaz, the Doppler Effect.
        With super massive stars, however, gravity also causes the 
redshifts. This makes it very challenging, especially with Quasars.  
They have huge redshifts.  So how much is due to super high 
velocity and how much is due to super high mass and gravity??

     THE GREAT MURAL QUADRANT: A device similar to a large 
protractor. It was invented by the famous TYCHO BRAHE in the 16th 
century for measuring the angles of the heavenly bodies.  With his 
good measurements others, like JOHANNES KEPLER, were able to 
accomplish great discoveries in astronomy.

     TEMPERATURE of STARS is determined by their colour.  This is 
called the spectral class.  An optical pyrometer can detect color of 
incandescent objects by comparing their colours to those of samples 
of known temperature.

     RADIATION OF STARS obeys the Stefan-Boltzman Law which says 
that the emission of energy is proportional to the fourth power of 
the absolute temperature.


                 E = k T4th   T is in K


     MAGNITUDE OF STARS:
        Absolute Magnitude or Illuminosity is a measure or the 
radiation being emitted by a star.  It is independent of distance.
        Apparent Magnitude, what it looks like to us, depends upon 
absolute magnitude and distance (remember the Inverse Square 
Law).
        The Magnitude scale was invented by Hipparchus in the 2nd 
century BC. First magnitude stars were the brightest ones, Sixth 
magnitude stars are the dimmest we can see (naked eye). By this 
scale, here are some examples: Sun = -26, Full Moon = -12, Venus = 
-4, Binoculars can see to 10, the 5-meter telescope to 24.


     VARIABLE STARS expand and contract and thereby vary their 
intensities.
        There are three kinds of variable stars. PULSATING change 
regularly.
        ERUPTIVE don't mess around... It's BAM, like a Nova. ECLIPSING 
binaries in which one star moves in front of the other as it orbits.

     CEPHEID VARIABLES are yellow supergiants. (Polaris, the North 
Star, is one. It varies between magnitude 2.5 to 2.6). Their size 
pulsates about 8%. They appear to be vibrating in resonance 
between the pressure of light pushing them out and gravity (their 
weight) pulling them in.  They are very important because there is a 
relationship between their periods of vibration and their 
illuminosity. This makes them useful in determining the distance to 
galaxies, far, far away. This is done by comparing their absolute and 
apparent magnitudes. That is, we know how bright that type of star 
is, and using the inverse square law, we can determine how far they 
must be to appear as bright as they are.



ASTRONOMICAL PHENOMENA:


     ROTATION OF THE EARTH.  From the poles, the stars make a 
complete circle in 24 hours.  Who is moving?  Us or them?  The 
FOUCAULT PENDULUM shows that it is the earth that is turning on 
its axis.  A pendulum's plane of vibration is independent of rotation, 
so the apparent rotation is the earth turning beneath the pendulum. 
The earth rotates 15deg per hour.  That's a time zone.

     REVOLUTION OF THE EARTH. The earth revolves about the sun at 
a rate of 18 km/sec in order to make its trip in about 365.25 days.

     REVOLUTION OF THE SUN. The sun makes a revolution around 
the galactic center in 200 million years.

     ECLIPSES are events in which one body blocks off light from 
another.

     A SOLAR ECLIPSE occurs when the moon blocks off sunlight from 
the earth. (The moon is between us and the sun).
        The reason that solar eclipses are rare, is because the cone of 
shadow, the UMBRA from the moon makes a spot only about 200 
km in diameter on the earth.
        A partial eclipse can be seen if you are in the PENUMBRA, 
which is the dim shadow surrounding the UMBRA.  It is caused by 
rays that pass the moon from the opposite side of the moon. 

     AN ANNULAR ECLIPSE of the sun is an event in which one can see 
a ring of sunshine around the moon. It is caused by the moon's 
being sufficiently far away from the earth that the UMBRA is in 
space above the earth and the sun's rays have diverged before 
reaching the earth. 

     TIDES are caused by both the sun's and the moon's gravity acting 
on the earth.  There is both a direct tide (same side as the sun and 
moon, and an opposite tide.  The latter is due to the relative forces 
of vector addition.  

        NEAP TIDES (medium highs and medium lows) are the result of 
the sun and moon being at right angles to each other such that their 
vectors somewhat cancel.  The moon's gravity vector is much 
stronger than the sun's because of the closeness of the moon.

        SPRING TIDES (high highs and low lows) are the result of the 
sun and moon being in line thus, adding their gravity vectors.

     A LUNAR ECLIPSE occurs when the earth blocks off sunlight from 
the moon. (The earth is between the sun and moon).
        The reason why lunar eclipses are only seen every few years 
(much more often than solar eclipses, however,) is because the 
moon's orbit is tilted with respect to that of the earth. Hence, only 
on special occasions do we have the Sun, Earth, and Moon directly 
in line.  When eclipsed, the moon has a reddish (oooh mysterious) 
glow due to the refraction and absorption of the sun's rays passing 
through the earth's atmosphere.

     PHASES OF THE MOON are the areas of it that we see illuminated 
as a result of our angle of viewing.  These occur monthly as Full, 
Quarters, Half, and New Moons.

     THE HARVEST MOON is the full moon nearest the Autumnal 
Equinox. What's special about, it is that it is up early for several 
days so that one can harvest his stash by moonlight.

     SUNSPOTS are cooler regions on the sun's surface caused by 
cyclonic (rotational) storms (ah the Coriolis Effect). Surface of the 
sun is 6000 K, the spots are about 4000 K.
        Galileo used sunspots to determine the sun's rate of rotation.

     NEBULA are gaaasss clouds composed mainly of hydrogen.  
Famous nebula are the Horsehead, the North American, the 
Dumbbell, and the Crab. The Crab nebula is the result of a 
supernova that occurred in the eleventh century.  It was so bright 
that it could be seen in the daytime for several weeks.

     SEASONS are caused by the tilt of the earth's axis, 23.5 deg.  Even 
though we, in the northern hemisphere, are closer to the sun in our 
winter, we have winter weather because the sun's rays are coming in 
at a great angle.  The density of sunlight per square centimeter, is 
much less than in summer when the sun is high in the sky.

     SOLSTICES are the maximum distance that the moon moves 
above or below the equator.  They are 23.5 degrees North and South 
Latitudes.  They occur on the first day of winter, the Winter Solstice, 
and the first day of summer, the Summer Solstice. Solstice literally 
means "stands still", that is the sun stands still at that latitude for a 
day before is starts back.

     EQUINOXES are the time when the sun is directly over the 
equator. The day and night are equal in length (equal night).  They 
occur on the first day of Spring, the Vernal Equinox, and the first 
day of Autumn, the Autumnal Equinox.

     SIDEREAL TIME is star time, measured by our position in space 
relative to the stars.

     MEAN SOLAR TIME is the average of the time in a year.

     THE EQUATION OF TIME is the difference between apparent time 
(by the sun, like with a sundial) and mean solar time (average over 
the year). It is about 14 minutes at most.

     BLUE SKY is caused by the short wavelength blue light being 
scattered by particles of matter in the atmosphere.

     RED SUNSETS and SUNRISES are caused by the sunlight passing 
through a long distance, when low in the sky, such that the blue has 
been scattered out, and only the long waves of red get through.

     PRIMARY RAINBOWS are caused by sunlight entering droplets of 
water at the top, refracting, totally reflecting, and refracting again.  
Red rays bend the least, violet ones the most, so that a colour 
separation occurs.

     SECONDARY RAINBOWS are caused by the sunlight entering the 
water droplets at the bottom, being refracted, twice totally reflected, 
and refracted again. (Wow).  




     THE DOPPLER EFFECT: When there is relative motion between a 
wave source and a detector, there will be a shift in the frequency 
that the detector notices.  For sound waves, approaching sources 
will have a higher frequency (higher pitch) and receding sources a 
lower frequency (lower pitch).  For light waves, the frequency 
changes result in color changes. Approaching waves have a blue 
shift and receding waves have a red shift.  This is detected by 
comparing the spectral lines of the moving source with those of a 
stationary source.  The amount of shifting enables one to calculate 
the relative velocity of the source and the receiver.

     CORIOLIS EFFECT is the apparent deviation of objects, air 
currents, or water currents moving over the rotating earth. The 
reason for this deviation, is because the earth moves at different 
speeds at different latitudes.  In the northern hemisphere, the 
deviation is to the right.  A ballistics missile fired from the North 
Pole aimed at New York and traveling for an hour would hit Chicago!


     GEOCENTRIC CONCEPT is the ancient idea (supported by 
Aristotle) that the earth is the center of the universe.

     HELIOCENTRIC CONCEPT is the modern idea (proposed by 
Copernicus in the 16th century, and proved by Galileo) that the sun 
is the center of the solar system.

     NEWTON'S FIRST LAW OF MOTION.  Every body either remains at 
rest or in constant motion in a straight line, unless acted upon by an 
external force.

     NEWTON'S SECOND LAW OF MOTION.  The acceleration of a body 
is directly proportional to the force and inversely proportional to 
the mass.

                    A = F/M,  or  F = MA

     NEWTON'S THIRD LAW OF MOTION. For every action there is an 
equal and opposite reaction.

                      Mv =mV.

     NEWTON'S LAW OF GRAVITY.  Every body attracts every other 
body with a force that is directly proportional to the product of 
their masses and inversely proportional to the square of the 
distance between their centers.

                           F = G Mm/r2

                                       G is the gravitational constant.
                                       M is mass of large object.
                                       m is mass of small object.
                                       r is the distance between centers.


     ORBITS are the balance between the forces of gravity trying to 
pull one object into another object and the effect of inertia, 
centrifugal force, trying to keep the orbiting object moving in a 
straight line.

                         F gravity = F inertia

                             G Mm /r2  = mv2
                              

     KEPLER'S LAW OF PLANETARY ORBITS:  The orbits of the planets, 
or comets,  are ellipses with the sun at one focus. (The other focus is 
a point in space).

     APOGEE is the most distant point of the orbit. 
              (Aaaaaaappoooogggeeee...  is waaayyy out).

     PERIGEE is the closest point of the orbit.


     KEPLER'S LAW OF EQUAL AREAS: The area that an orbiting planet 
sweeps out of its ellipse is always equal in an equal time. This law 
enables one to calculate where a planet or comet, any other orbiting 
body will be at any time. (The velocity of an orbiting body changes 
with distance from the sun, moving more slowly when it is more 
distant).

     KEPLER'S LAW OF PERIODS:  The period squared is equal to the 
distance cubed of an orbiting planet, or comet. This enables us to 
calculate the length of a year on any planet when we know its 
distance from the sun.  It applies also to the time for a comet to 
come around again.  For example COMET HALLEY comes around 
every 76 years.

     THE PLANETS:  To remember them in order from the sun...

   "Mary's  Violet  Eyes  Make  John    Stay    Up   Nights  Pondering."
   Mercury  Venus  Earth  Mars Jupiter Saturn Uranus Neptune  Pluto

        Because Mercury and Venus are inside the Earth's orbit, they 
exhibit phases just like the Moon does (full, quarters, half, and new).

     GALILEO improved the telescope in the 16th century, and 
discovered four  satellites of Jupiter, and Galaxies (which he thought 
were blurs).  His telescope was not nearly as good as a cheap pair of 
binoculars, so go out see for yourself!

     BINARY STAR a pair of stars orbiting about each other under 
mutual gravitational attraction. One can learn the masses of the 
stars from Newton's Law of Gravity and knowing the period of 
revolution of the binaries. A famous binary star is Barnard's Star.

     GALAXY.  A large system of stars held together by mutual 
gravitational attraction. Ours is the Milky Way.  Nest nearest is 
Andromeda.

     THE MASS OF THE GALAXY can be found using the binary star 
technique with the sun as one star the center of mass of the galaxy 
as the other.  The result is a galactic mass of 200 billion sun's 
masses.

     SPIRAL GALAXY is a galaxy that has spiral arms.  The Milky Way 
is a spiral galaxy as is Andromeda.

     ELLIPTICAL GALAXIES are lens shaped.

     IRREGULAR GALAXIES are a mess.

     SYFERT GALAXIES are unusual spiral galaxies characterized by 
small, extremely bright nuclei containing one to ten billion stars.  
They are orders of magnitude brighter in the X-ray than in the 
visible part of the spectrum.

     BLACK HOLE.  An object resulting from complete gravitational 
collapse beyond that of a neutron star. The accompanying 
gravitational field is so intense that no radiation can escape.  It must 
be a star of at least ten times the mass of our sun.
        The EVENT HORIZON is distance that once entered offers no 
escape.  Not even light can get out.  The X-rays emitted are from 
atoms that are being torn apart as they enter the event horizon.  At 
this place, the gravitational gradient is so severe, that even atoms 
are torn asunder.

     COSMIC RAY. High energy atomic nuclei (ions) and electrons 
originating in stellar sources and interstellar space, and observed in 
the near-earth environment.

     COSMOLOGY is the study of the origin, evolution, and structure 
of the universe.

     DIFFUSE BACKGROUND is the microwave radiation that pervades 
all of space and is believed to be a remnant of the initial big-bang 
which marked the birth of the universe.

     THREE DEGREE RADIATION (3 K, or 3 deg C above absolute 
zero).   See Diffuse Background.

     EXPLODING GALAXIES are violent energetic explosions centered 
in certain galactic nuclei where the total mass of ejected material is 
comparable to 5-million average stars.  Jets of gas 1000 light- years 
long are typical.

     GENERAL RELATIVITY is the theory of gravity and the nature of 
gravitational forces as expounded by Einstein.  He said the masses of 
matter cause deformations in space (like vortexes), into which 
matter falls, spirals around, or orbits..

     SPECIAL RELATIVITY is Einstein's theory (or fact) dealing with 
matter as it approaches the speed of light (300,000 km/sec). It 
shows that at speeds approaching that of light (which is the 
maximum speed), matter shortens in the direction of motion, gains 
in mass, and time slows down... All relative to the observer.
        This has been proved in particle accelerators wherein electrons 
find long tubes (like the 3 Km one at Stanford) become short (a few 
cm), and their masses gain 40,000 times!!
        Furthermore, particles' time of decay slows down as predicted. 
Also, super accurate clocks placed on aircraft moving relative to the 
earth run more slowly than those on the ground!
              We're talkin' impressive action!

     METEORS are luminous phenomenon observed in the atmosphere 
composed of small particles of matter.  Sometimes called, "shooting 
stars". The friction of the atmosphere heats them so hot that ions 
are produced and sometimes the meteor explodes. The ionized air 
causes the streak of light we see.

     METEOROID is a particle in space before it encounters the earth's 
atmosphere.

     METEORITE is that part of the meteoroid which survives the 
intense heat of atmospheric friction to reach the earth.

     AURORAS, (Aurora Borealis, Aurora Australis), are light radiated 
by  atoms stimulated by solar radiation in the atmosphere around 
the magnetic poles. They are especially active during big sunspot 
action.

     ASTEROIDS are minor planets orbiting between Mars and Jupiter. 
The largest is called Ceres.

     SUPERNOVA.  This is a catastrophic stellar explosion occurring 
near the end of a star's life in which the heavy elements are created 
and spewn out into space. Visible luminosity may reach 100-million 
times that of the sun. Our most famous one blew in the eleventh 
century, and is still spreading out a gas cloud called the Crab 
nebula.


     NEUTRON STARS are remnants of supernovae explosions.  They 
consist of ultra-dense matter composed almost entirely of neutrons, 
which have been squeezed together by the force of gravity exerted 
by the collapsing matter. The extreme pressure and temperature 
crushes the atoms together and forces the electrons into the protons 
to make neutrons. They are about 60 km in diameter with the mass 
of thousands of suns!!!  Gasp...

     PULSARS are believed to be rotating neutron stars.  The intensity 
of their radiation in the electromagnetic spectrum is modulated by 
the period of rotation. These are radio sources. Only one has been 
visually sighted.  It is in the Crab Nebula.

     QUASARS, or Quasi-Stellar Objects, are very controversial. 
Quasars seem to be the size of large stars, yet they emit energy at all 
wavelengths comparable to that of a thousand galaxies. They are the 
brightest and most distant objects in the universe, and they are 
characterized by very large redshifts.  Overwhelming!!

     X-RAY SOURCES are detected by radio telescopes.  X-rays are 
possibly the death cries of matter entering black holes.

     WHITE DWARF is a star the size of the earth formed from a 
collapsed star about the size of the sun.

     RED GIANT is a very large and cold (only red hot) star.  It doesn't 
have the poop to become a nova.  The most famous is Betelgeuse. 
(Pronounced "beetle juice").  It is so large that if it were placed 
where our sun is, it would fill most of the solar system. 

     BLUE GIANTS are young stars, rich in hydrogen, and burning 
HOT. Many dazzling ones can be seen at night, including the 
Pleiades (seven sisters), Sirius and Spica.

     H-R DIAGRAM (Hertzsprung-Russell) is very important!!!  Look it 
up in an astronomy text!  Note how the different spectral types are 
placed in and around the main sequence of stars. Our sun is an 
average star in the main sequence.

     STARS POPULATIONS.  Population I are the young blue stars.  
They are mostly hydrogen, and are fusing it into helium. Population 
II stars are old red stars.  They have a high concentration of helium.
        When a star ages and cools off, its light pressure diminishes 
allowing gravity to cause the star to start collapsing.  If it is large 
enough to create sufficient heat by adiabatic compression, other 
elements will undergo nuclear fusion (the light elements down to 
iron).  This can cause the star to explode and become a NOVA.
        When it becomes a NOVA or SUPERNOVA, the heat is so 
tremendous that heavy elements (beyond iron) are formed.  We're 
talking millions and millions of degrees K. The heat is ON!


     PARTS of the SUN:  The sun is over 1-million kilometers in 
diameter (the earth is 12,000 km).  It is surrounded by the CORONA 
which is a halo of white light extending a million Km.  It can be seen 
during an eclipse of the sun.
        The CHROMOSPHERE is a bright red ring layer of gas 100,000 
km thick. The surface temperature is 6000 K.
        The INTERIOR is a dense mass of gases at a pressure of 1-billion 
megagrams (metric tons) per square centimeter!  The temperature is 
15-million K.

     SUNSPOTS are colder (4000 K) cyclonic storms that have high 
magnetic fields about them.  These fields guide the solar flares in 
horseshoe patterns.

     SOLAR FLARES or PROMINENCES are streamers of gas erupting 
from sunspot activity. The eruption causes great radio disturbance 
here on earth due to the ions produced.  A famous example was the 
attempt of the military in Washington to warn Pearl Harbor of the 
pending Japanese attack after they had broken the Japanese code.  
The solar flare in progress prevented the radio messages from 
reaching Hawaii. Hence a telegram was sent but arrived too late.


     THEORIES OF THE FORMATION OF THE UNIVERSE:  
     
     The STEADY STATE theory states that matter is constantly being created to 
replace that which is consumed or moves on.  This isn't highly 
upheld anymore.
        THE BIG BANG theory states that all the matter/energy was for 
an instant concentrated in one blob, and then it blew! And it's still 
blowing.  If we extrapolate the presently expanding universe back to 
where it appears to have started, it's 15-billion years old.
        THE PULSATING UNIVERSE theory thinks that instead of 
expanding forever, it will stop its expansion, and contract back to a 
blob again and start all over with another big bang. This could 
happen if there is enough mass to exert sufficient gravity to stop the 
expansion.

     THEORIES of FORMATION of the SOLAR SYSTEM: In 1778, le 
Compt de Buffon established the PLANETESIMAL HYPOTHESIS.  It 
says that two stars came close together and their gravities pulled 
forth gases that cooled and condensed into solid chunks of matter 
that coagulated into the planets.
        It is more likely that a big gas cloud whirlpool condensed into 
the sun and its planets.  This is called the DUST CLOUD WHIRLPOOL 
HYPOTHESIS of von Weizsacker.

             HERE ENDETH THESE NOTES. 

Much more can be found in astronomy texts including the 
appropriate pictures and diagrams.


