Astron 088: Final

Infrared

Substantial amounts are emitted by cool stars, but most wavelengths of IR radiation are absorbed by water vapor in the Earth's atmosphere.

UV radiation

Substantial amounts are emitted by energetic processes and hot stars, but it is is also mostly absorbed by the ozone in the Earth's atmosphere.

Alighieri(Dante)

1300s - made drawings which showed the location of heaven and hell in the Aristotelian universe based on the teachings of Thomas Aquinas; became one of the foundations of the Christian Church at the time

Ptolemy

140 AD - refine the Aristotelian model of the Universe with a system of epicycles that would explain retrograde planetary motion. Wrote the Almagest

Hipparchus

150 BC - one of the first to catalog brightnesses and positions of stars in a very comprehensive way, introduced epicycles

Brahe(Tycho)

1546-1601 : never used telescopes but considered incredibly accurate especially on his observations of mars. enabled kepler to produce his 3 laws of planetary motion

Kepler

1571-1630: showed that the sun centered(heliocentrc) model of the universe worked better if the planets were in elliptical orbits about the sun of circular orbits. Three laws of planetary motion

Newton

1642-1727 AD - great synthesizer of experiments and observations who put forth the Theory of Gravity (for example, he explained Kepler's empirical 3rd Law and modified it so that it could be used to calculate the mass of a body); he also invented the reflecting telescope, calculus, and did important experiments in optics and light along the way.

Eratostothenes

250 BC - emphasized math, made observations of the angle of the sun with respect to zenith at different latitudes which allowed him to calculate the circumference of the Earth

Aristarchus

280 BC - put forth a sun centered model for the universe, but it was not accepted because stars did not exhibit parallax, which was expected if the earth went around the sun because people assumed the stars were nearby. He deduced the relative sizes of the sun and the moon

Aristotle

350 - emphasized metaphysics - he is credited ith developing a well thought out model of the universe(earth at the center) that persisted until the 1500s

Plato

380 BC - emphasized metaphysics, the pupil of Socrates and Aristotle's teacher; emphasized the importance of the circle in models

Pythagoras

540 BC - emphasized math; used numbers and geometry to express relationships in nature

Thales

600 BC - emphasized metaphysics; one of the first to propose a model for the universe, namely that the Earth was a disk afloat on the giant sea

Coriolis deflection

A missile fired from the north pole toward a target on the equator would find that the intended target rotates away.

Spectrograph

An instrument that separates light into colors and makes an image of the resulting spectrum.

Size of Earth relative to moon

Aristarchus found the Moon is 35% of Earth's size (actual is 27%). Used lunar eclipses. Note the size of the Earth's shadow relative to the Moon's size.

Relative Sun-Moon Distance

Aristarchus found the Sun was 20 times more distant than the Moon. (Observational error The Sun is 400 times more distant than the Moon!). Had to use either the first or third quarter moon

Kepler's Second Law

As a planet moves around its orbit, it sweeps out equal areas in equal times

Continuum Spectrum

By passing visible light produced by a hot filament through a prism, it can be broken up into a continuum of its component energies. Short wavelength violet light is the most energetic visible light, while long wavelength red light is the least energetic visible light. Colored filters can be used to transmit only certain wavelengths (colors) of light.

Theocratic World View

Based on the theology of Thomas Aqcuinas, including a place for heaven and hel

400x larger

Compared to the size of the Moon the absolute size of the Sun is:

About the same

Compared to the size of the Moon the angular size of the Sun is:

Fred Hoyle

Developed an arbitrarily complex way to use stonehenge to predict eclipses. 56 Post holes divided by 3

The moon is at it's highest point in the sky when the sun is setting

During a first quarter moon as viewed from pitt

Lipershey

Dutch lens maker often credited as the first to build a refracting telescope (but not for astronomy).

Greek: 8200 miles, Modern: 7,927 miles

Earth Diameter

Aristotelian World View

Earth centered, geocentric model which used rotating crystalline spheres

L=(2(pi)D)/360°

Eratosthenes calibration to find the actual distance of the sun and moon. L = diameter of planet, D = distance to planet.

Newton's Second Law

F=ma

Newton's Third Law

For every action there is an equal and opposite reaction

Ptolemaic world view

Geocentric model which used epicycles to explain planets' retrograde motion

29.5 days

How long does it take for the moon to complete a set of phases?

Sidereal year

If we observe the Sun, we find that the Sun takes about 365.2564 mean solar days to return to the same point in the sky with respect to the background stars.

No, need at least one side

If you know the 3 angles of a triangle, you also know the absolute lengths of the 3 sides?

Precession of the equinox

In this effect, the Earth's axis, which is tilted 23.5° with respect to a line perpendicular to the plane of the Solar System, gyrates (or precesses) with a 26,000 year cycle. During a single human lifetime, this effect would not be detected by a casual observer of the sky.

Newton's First Law

Inertia

Galilei, Galileo (1564-1642)

Italian astronomer. 1564-1642 AD - he did important experiments which helped reveal the laws of falling bodies; he also made observations with a telescope (he put together the first refracting telescope used for astronomical observation) which supported the heliocentric theory.

Ganymede, calliso, io, Europa

Jupiter's 4 largest moons

Inverse Square Law

Light intensity (and gravity!) decreases according to the square of the distance, D, from the source. Similarly the surface area of a sphere depends on its radius squared.

Visible Radiation

Moderate temperature (6000° Kelvin) stars like the Sun emit a large fraction of their energy at visible wavelengths. Visible light (which is a very small part of the EM spectrum) passes through the Earth's atmosphere. The different types of visible light are: Violet (shortest wavelength), Indigo, Blue, Green, Yellow, Orange, Red (longest wavelength). Some people memorize this in reverse order by remembering the name Roy G. Biv.

Greek: 2870 miles, Modern: 2,160 miles

Moon Diameter

Greek: 318000 miles, Modern: 239,000 miles

Moon Distance

F=GMm/D^2

Newton's Law of Universal Gravitation. G=constant, M and m are the two masses of attracting bodies, and D is their separation.

20x zoom

Refracting power of Gallileo's telescope

If the phase of the moon is new

Side of the moon seen from earth is not illuminated. A solar eclipse can occur.

Sun's Diameter in relation to moon

Since the angular sizes of the Sun and Moon are the same, early Greeks also inferred that the Sun's diameter was 20 times larger than the Moon's. (Observational error è it's actually 400 times larger.)

Greek: 57,400 miles, Modern: 864,000 miles

Sun Diameter

Greek: 6,200,000 miles Modern: 93,000,000 miles

Sun Distance

Copernican

Sun centered(heliocentric) model which used a rotating earth and more naturally explained planets retrograde motion

Circumference of Earth

Sun's angle at noon at different latitudes. Eratosthenes determination was precise, accurate to 3%.

Tycho Solar System

The Sun and Moon went around the Earth, but everything else went around the Sun

100, 900

The UK had over ___ henge monuments and over ___ ceremonial circles

Tides

The high tide on the side of the Earth near the Moon is a result of water being pulled away from the Earth and toward the Moon, but the high tide on the side of the Earth which is opposite the Moon is a result of the Earth being pulled away from the water and toward the Moon. Low tide occurs between high tides. Tides change every 6 hours 12 minutes

Ecliptic

The location of the celestial equator in the sky is fixed for an observer on Earth, while the changing location of the Sun (corresponding to the constellations of the Zodiac) throughout the year is defined by this

Penumbra

The part of a shadow surrounding the darkest part

Seasons

The plane defined by the Earth's rotation (i.e., the celestial equator) is inclined 23.5° with respect to the Earth's orbital plane (i.e., the ecliptic plane, which is approximately the plane of the Solar System). This angle between the celestial equator and ecliptic plane is called the obliquity of the ecliptic and is 23.5°.

Absorption Line Spectrum

The spectrum of a gas seen in front of a continuum spectrum shows absorption lines. The absorption lines are produced at very specific wavelengths as electrons in the ground states are excited to higher states when they absorb continuum photons.

Emission Line Spectrum

The spectrum of a hot tenuous gas shows emission lines. The emission lines are produced at very specific wavelengths as electrons in specific excited energy states fall down to lower energy states (like the ground state).

Kepler's Third Law

The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.

Gallileo's telescope observations

There are many stars too faint to see without telescope. Nebulous blurs are resolved into many stars. Jupiter has 4 large satellites/moons; it's like a minisolar system.

X-Rays

They are also emitted by very energetic processes and are absorbed by the ozone in the Earth's atmosphere.

Gamma Rays

They have the greatest energies and shortest wavelengths. They are emitted by very energetic processes, but can be best observed in astronomical objects using space telescopes because ozone in the Earth's atmosphere absorbs most gamma rays.

Radio Waves

They have the smallest energies and longest wavelengths. Substantial amounts are emitted by plasmas sometimes associated with magnetic fields. Radio waves pass through the Earth's atmosphere.

Spring Tides

Tides are maximized near new and full moon phases

Neap Tides

Tides are minimized near quarter moon phases

Inner Stones

Used to predict seasons in stonehenge

Doppler Effect

When a wave is emitted by an object which is moving toward you, the wavelength is seen to decrease. Similarly, when a wave is emitted by an object which is moving away from you, the wavelength is seen to increase. The amount of increase or decrease in wavelength allows one to calculate the velocity difference between you and the object. Sound waves are not EM radiation. However, sound waves can be used to demonstrate how the wavelength (or frequency) depends on velocity

Increase

When an elevator starts accelerating upward, your weight as measured on a scale will:

Absolute Magnitude

a unit of measure that astronomers use to specify the actual or intrinsic brightness (luminosity) of a star. For example, the actual or intrinsic brightness (luminosity) of a light bulb is given by its wattage.

Apparent Magnitude

a unit of measure that astronomers use to specify the apparent or perceived brightness of a star. The apparent magnitude of a star depends both on the star's absolute magnitude and the star's distance.

Gravitron

a wave-like particle with zero rest mass and no charge. Gravitons are the "exchange particles" or carriers of information in gravitational theory. Gravity acts on all mass, e.g., it holds the stars, solar systems, and galaxies together.

Tycho's Nova

actually a supernova, an indication that the sky is changing, challenging aristotle's idea. Also discovered a comet that was beyond the moon's orbit. Challenged aristotle.

annular eclipse

an eclipse of the sun in which the edge of the sun remains visible as a bright ring around the moon.

Photon

another word for electromagnetic (EM) radiation. Certain photons are also the "exchange particles" or carriers of information in electromagnetic theory, i.e., the theory that explains how atoms are held together. Gamma rays, x-rays, ultraviolet light, visible light, infrared light, and radio waves are all types of electromagnetic radiation.

Radio Telescope detector

antenna with a receiver

Tidal Bulge

caused by the differential gravitational force that the Moon exerts on the Earth's waters. This differential gravitational force arises because a portion of the Earth's surface is always 8,000 miles closer to the Moon than is the surface on the opposite side of the Earth.

Coriolis Effect

caused by the rotation of the Earth on its axis with respect to the fixed stars. For example, a pendulum located at the north pole would demonstrate this rotation nicely as the Earth would rotate under it during the course of a day.

Inertia

causes objects of mass to resist changes in motion (speed and direction): Larger mass means more resistance to motion.

Collecting area

determines how much EM radiation from an object can be collected and focused in a given interval of time. This is basically the telescope's light gathering power. By making the collecting area larger, fainter objects can be observed. For unobscured spherical optics, the collecting area is simply A = πD2 /4, where D is the telescope diameter. If a point-source star is being observed, its image brightness, B, in an aperture containing the star will be directly proportional to the collecting area, A

Bruno

first to suggest we live in a universe with the sun not at it's center and that there are many solar systems, burned at the stake for blasphemy

Kepler's First Law

elliptical orbits for planets (not circular orbits)

Copernicus

first to propose a sun centered model of the universe that became wildly accepted. inferred that, because parallaxes of stars were not observable (by eye!), the stars must be at great distances, consistent with his heliocentric theory.

Reflecting Telescopes

focus light with mirrors. There are numerous designs for reflectors (e.g., Newtonian, Cassegrain, Gregorian, Ritchey-Chretien, etc.) that vary in cost, but generally they are considerably cheaper than refractors because there are less surfaces to grind and polish. Aberrations in the image are determined by the design, but spherical aberration is a common problem in reflectors and is corrected by making the shape of the mirror parabolic.

Relation of Apparent Brightness and distance

governed by the inverse square law: the apparent brightness is inversely proportional to the distance to the object squared. [For example, if we were two times further from the Sun, the Sun would appear 22 = 4 times fainter; if we were 10 times further from the Sun, the Sun would appear 102 = 100 times fainter.]

Hooke

great scientist of his time, but he often wrongly criticized Newton. Named Cells

Solar Eclipse

happens when the phase of the Moon is NEW(and no any other) and the Moon is between the Earth and Sun.

Theoretical Resolution

how well two nearby objects are separated) depends on the wavelength of the EM radiation and the distance (baseline) between different parts of the telescope's collecting area. Observations at longer wavelengths result in poorer resolution. Smaller distances between different parts of a telescope's collecting area also result in poorer resolution.

Constant acceleration due to gravity

independent of the body's mass. Galileo used an inclined plane to slow down how long it took a body to reach the ground in order to measure acceleration caused by gravity.

Equatorial Mount

most commonly used by amateur astronomers to observe the sky. The mount's polar axis is pointed toward the north celestial pole, i.e., toward the north star. The other axis, called the declination axis, is perpendicular to the polar axis.

Moon revolves around the earth

once each month. This means that each day the Moon moves about 12° east with respect to the background stars.

Digges

one of first to seriously introduce the concept of infinity into a model of the Universe

Rheticus

prompted Copernicus to publish his great work

Halley

prompted Newton to publish his great work, Principia; discovered "Halley's Comet."

Air Friction(resistance)

slows down a falling body.

umbra

the very darkest part of the moon's shadow

Photometer

used to measure the intensity of light from an object. Modern photometers are often just CCDs used with colored filters.

Aurora

usually arise when charged particles are produced by a solar storm (more common at sunspot maximum). The charged particles become part of the solar wind. When the particles encounter the Earth's magnetic field, they are guided by the magnetic field toward the poles. When they finally hit the molecules in the atmosphere a glow is produced. This is a beautiful effect that sometimes appears in a variety of colors.

Refracting Telescope

which focus light with lenses. These telescopes are costly because there are more optical surfaces to grind and polish. Refracting telescopes also often suffer from chromatic aberration (i.e., all the different colors of light from an object are not focused at the same place). However, refractors can produce superb images if made properly.

Elementary Particles

with exotic sounding names (intermediate vector bosons and gluons) are thought to be the "exchange particles" in weak and strong nuclear theory. The weak theory explains radioactive decay while the strong theory explains how atomic nuclei are held together.