*** 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.