SDSU Astronomy Final Leonard

fundamental forces of nature

the basic forces that are known to exist in Nature

gravity

electricity

magnetism

strong nuclear force

weak nuclear force

star

a sphere of gas shining under it's own power

-mainly made up of H and He

-nuclear fusion of light nuclei into heavy nuclei produces the energy by which they shine

--considered to be "living" from the moment nuclear fusion begins, until the moment it stops

--fate of a star depends entirely on its initial mass

-an object that during some part of its lifetime derives 100% of its energy from the fusion of hydrogen nuclei (protons) to helium

-supported by gas pressure and radiation pressure

-stars are born with a range of masses

--lightest stars have ~0.1Msun (min. amount of mass that an object must have in order to achieve temp high enough to ignite fusion of H into He in its core

--heaviest stars have ~100Msun

--most stars have less mass than the sun

--greater the mass, the more luminosity

--maximum core temp achieved by a star depends entirely on star's mass. greater mass=greater temp

Alpha Centauri

the closest star (takes 4 years for light to reach us)

light year

the distance light travels in one year

nebula

any "fuzzy" astronomical object

north pole

northern most point

south pole

southern most point

equator

circumference midway between two poles

latitude

the angular distance north or south of the equator

longitude

angular distance around the earth, measured along the equator

sun

large, self-luminous sphere of gas, closest star to earth

-gas pressure dominates in sun, but both gas and radiation pressure support are important for stars

-generates power through nuclear fusion

-nuclear fusion in the sun releases neutrinos, which have been detected on earth, confirming our basic model for the sun's energy source

-sun is in hydrostatic equilibrium

-~4.5 BY old, and will continue fusing H --> He for another ~4.5 BY

-sun will become a red giant about 10 billion years after its born

horizon

-the boundary that divides what you can and can't see in the sky.

-sun rises in the east and sets in the west

celestial sphere

-imaginary sphere centered on the center of the Earth to which it "appears" the stars are affixed

conceptual scheme

a "model" used to explain observations

zenith

90 degrees north of the horizon of where you are standing

celestial poles

extension of earth's north and south poles onto the celestial sphere

celestial equator

extension of earth's equator onto the celestial sphere

Polaris (north star)

-a fixed star on the celestial sphere that does not move

-zenith to the north pole

circumpolar stars

-stars that never rise nor set, but just circle around a celestial pole

-above the horizon at all times

-at the north pole, all stars are circumpolar

-at the equator, no stars are circumpolar

"wanderers"

Sun, moon, mercury, venus, mars, jupiter, saturn

ecliptic

-apparent annual path of the sun on the celestial sphere

-takes about a year for sun to return to it's original spot

constellation

one of 88 sectors into which astronomers divide the celestial sphere

asterism

an especially notable star pattern in the sky

zodiac

a belt around the sky about 18 degrees wide, centered on the ecliptic

retrograde motion

the apparent motion of a planet when it appears to move "backward" from the direction it normally moves with respect to the stars

parallax

the apparent displacement of an object caused by a change in the position from which it is viewed.

-The closer the object, the greater the parallax

-defined to be one half the angle that a star shifts when seen from opposite sides of Earth's orbit

-the apparent displacement of a nearby star due to Earth's motion around the sun

-can be used to find nearby stars (most accurate and least controversial technique)

-current range: up to ~300 LY

cosmology

the study of the whole universe, its contents, structure, origin, evolution, and ultimate fate

geocentric

explanation of Sun's apparent motion: sun circles around the Earth once per year

earth is at the center

heliocentric

explanation of Sun's apparent motion: Earth circles around the Sun once per year

sun is at the center

Eclipse

the passing of one body into the shadow of another

lunar eclipse

the phenomenon that occurs when the moon moves into the shadow of the earth

sun earth moon

why geocentric was preferred over heliocentric

-if earth was moving, we would feel it

-earth-centered is philosophically pleasing: humans are special in a special location

-Plato and Aristotle said so

-parallax of stars was not observed

Plato's challenge:

what are the uniform, circular motions that underly the observed motions of the planets in our sky?

epicycle

a small circle riding on a larger circle on which the planet moves

solar system

the system of the sun, planets, and other objects revolving around the sun

-formed roughly 4.5 billion years ago

celestial motions: a summary

-extremely complex

-geocentric cosmology, favored by ancients, perfected by Ptolemy in ~130 AD

-full, heliocentric cosmology not proposed until ~1540 AD by copernicus

telescope

an instrument that collects light and makes distant objects appear larger and brighter

-the larger the telescope, the fainter the objects that it can detect

-invented in 1608

-telescopes now exist to collect light from all regions of the electromagnetic spectrum; some are located in space (e.g., the Hubble Space Telescope) to get above Earth's obscuring atmosphere

testing theories: heliocentric vs geocentric

only the heliocentric model is consistent with the observation that Venus goes through a complete set of phases

the essence of science

the ability to make testable predictions

CORRECT explanations (heliocentric cosmology) for observations

1.all stars complete one revolution per day about the pole star

--> occurs due to the Earth rotating once per day about its axis of rotation

2. sun shares a daily east-west motion with all other celestial objects and also moves once per year in opposite (easterly) direction

--> occurs due to the Earth revolving once per year around the sun

3.planets appear to rotate once per day around the pole star, exhibit a slow easterly motion with respect to background stars, exhibit retrograde motion

--> occurs due to the Earth passing outer planets in their paths around the sun

4. venus and mercury never stray very far from the sun in the sky

--> occurs due to mercury and venus always being interior to the earth's path around the sun

precession

the slow, conical change in the orientation of Earth's axis of rotation that slowly changes the location of the celestial poles over time

-a complete cycle takes 26,000 years

astrology

the study of the possible influence that the locations of the sun, planets, and moon in our sky have on human affairs and destiny

Aristotle

very influential greek philosopher who presented arguments in favor of Earth having a spherical shape (~325 BC)

-believed in geocentric cosmology

-knew sun was further away than the moon

-shadow on moon during eclipse was round so he knew the earth was round

-when traveling far south you see new stars, and height of North pole decreases

-thought that heavier objects would hit ground first

-student of Plato

Eratosthenes

greek astronomer, mathematician, and geographer who successfully estimated the circumference of the earth (~200 BC)

Hipparchus

perhaps the greatest observational astronomer of ancient times (~150 BC), created a precise star catalog (locations and brightness) and discovered the precession of Earth's axis

geocentric?

Aristarchus

(~280 BC) believed in heliocentric cosmology

Claudius Ptolemy

(~140 AD) wrote Almagest and Tetrabiblos

-geocentric

-most important contribution was his geometrical representation of the solar system that predicted the positions of the planets for any date and time

De Revolutionibus

-by Copernicus

-most important idea was that Earth is one of six (then known) planets that revolve around the sun

-was able to work out correct general picture of the solar system

-deduced that the closer a planet is to the sun, the greater the orbital speed

-with this theory, was able to explain complex retrograde motions of the planets without epicycles

Nicolaus Copernicus

(1473 - 1543) cleric and scientist

-could not prove that earth revolves around sun

-first proposed full heliocentric cosmology in ~1540 AD

-wrote De Revolutionibus

-laid foundation for Galileo and Kepler

Galileo

1609, heliocentric

-the study of motion and the actions of forces on bodies

telescope discoveries:

-phases of venus

-jupiter's moons

-moon's craters

-sunspots

-milky way made up of "innumerable stars"

Johannes Kepler

(1571-1630) his discovery of basic laws that describe planetary motion placed the heliocentric cosmology from Copernicus on a firm mathematical basis

-WHAT are the precise paths taken by the planets as they resolve around the sun?

-developed 3 laws of planetary motion

Isaac Newton

(1643-1727) WHY do planets follow the paths that they do?

-3 laws of motion

-1666: disperses sunlight into a spectrum of colors (continuous spectrum)

Henrietta Leavitt

determined that cepheid stars can be used as standard candles (1910)

Vesto Slipher

(1875-1969) found that nearly all the great nebulae were found to be moving away from us at tremendous speeds (1917)

Edwin Hubble

Hubble's Law, Hubble Constant, Hubble Diagram

Hubble's orignial estimate: Ho=500 (km/s)/Mpc

Today's best estimate: Ho=70 (km/s)/Mpc

--todays estimate yields a time since the Big Bang of about 14 billion years

Cecilia Payne-Gaposchkin

(1900-1979) discovered the relative amounts of each element in the sun (1925)

Wolfgang Pauli

1933: proposed the existence of neutrinos

Tetrabiblos

the foundational book on astrology

Galileo's contributions to science and mechanics

-emphasized absolute necessity of experimentation

-law of falling bodies

-law of inertia

-principle of equivalence

mechanics

the branch of physics that concerns the study of motion and the action of forces on bodies

Law of Falling Bodies

in the absence of air-resistance, all bodies fall at the same rate

Law of Inertia

every body tends to continue doing what it is already doing - being in a state of rest, or moving uniformly in a straight line - unless it is compelled to change by an outside force

--only a change in motion requires a force

Galileo's Principle of Equivalence

there is no way to tell locally the difference between being in a reference frame that is at rest or one that is moving at a constant speed in a constant direction

--resolves the "why-don't-we-feel-the-Earth-moving" problem

asteroid

a small, stony, or metallic object orbiting the sun

asteroid belt

a region between the orbits of mars and jupiter in which many asteroids are located

volume

the physical space occupied by a body

density

amount of mass per unit volume

angular momentum

the momentum associated with motion around an axis or fixed point

-when a large, slowly spinning object collapses down to a smaller size, its spin rate increases in order to conserve angular momentum

Newton's Law of Gravity

gravity is a force of attraction that exists between objects that have mass

-an example of an inverse square relation: the force of gravity decreases as the inverse square of the distance separating the objects

Fg= (GxM1xM2)/R^2

-if you double the distance, the force decreases by a factor of 4

-if you halve the distance, the force increases by a factor of 4

-if sun were replaced by black hole with equal mass, nothing would change

-since light has no mass, it should not be affected by gravity

inverse square relation

the force of gravity decreases as the inverse square of the distance separating the objects

eccentricity

how "squashed" an ellipse is; the ratio of the distance between the foci to the length of the major axis

Kepler's Three Laws of Planetary Motion

1. each planet moves about the Sun in an orbit that is an ellipse, with the Sun at one focus of the ellipse

2. the straight line joining a planet ad the Sun sweeps out equal areas in space in equal intervals of time

3. the squares of the planet's periods of revolution are in direct proportion to the cubes of the semi-major axes of their orbits P^2=R^3 (P in years and R in AU)

Newton's Version of Kepler's 3rd Law

newton proposes that this law if Universal (it applies everywhere in the universe)

(R^3)/(P^2)=constant

where the "constant" is equal to the sum of the two object's masses

(R^3)/(P^2)=(M1+M2)

ALLOWS THE DETERMINATION OF MASSES BY STUDYING ORBITS

since M1 >> M2, (M1 + M2)~M1 so...

M1~(R^3)/(P^2)

measuring R and P essentially tells you the mass of the more massive object

solar eclipse

the eclipse of the sun by the moon, caused by the passage of the moon in front of the sun

sun moon earth

angular diameter

the angle subtended by the diameter of an object

both the sun and moon subtend angles of ~.5 degrees in our sky

corona

the outer atmosphere of the sun

solar nebula

the cloud of gas and dust out of which the solar system formed

planetesimals

small bodies that formed in the solar nebula that ultimately formed the planets

terrestrial planets

mercury, venus, earth, mars

any planet with mass ~ 1/10Mearth - 10Mearth, which orbits another star

jovian or giant planets

jupiter, saturn, uranus, neptune

astronomical unit (AU)

the distance from Earth to Sun

differentiation

the gravitational separation of materials of different density into layers in the interior of an object

Meteor:

A flash of light observed when a small piece of solid matter enters

meteroid

A particle or chunk of typically rocky or metallic material in space

before any encounter with the Earth.

Meteorite

A portion of a meteoroid that survives passage through Earth's atmosphere and strikes the ground.

Mercury

-closest planet to the sun

-orbits sun quickly (88 days)

-smallest (and least massive) planet

-hot (450 degrees F)

-no moons

-heavily cratered

Venus

-similar in size to Earth

-thick atmosphere

-experiences "runaway" greenhouse effect

-incredibly hot surface (1000 degrees F)

-no moons

-slow, "backwards" rotation (243 days)

Earth

-only planet (we know of) with life

-only planet (we know of) with liquid water on surface

-closest planet to the sun with a moon

The moon

-orbits Earth every ~27 days

-about 1/4 the diameter of Earth (very BIG relative to earth)

Mars

-comparatively small planet (only ~1/10 mass of Earth)

-rotates every 24 hours (like earth)

-no liquid water today, but likely had in the past

-has largest volcano in the solar system

-has two small moons (phobos and deimos)

Jupiter

-largest and most massive (by far) planet in the solar system

- no solid surface: the first of four "giant" planets

-similar chemical composition to the sun

-over 60 known moons

Saturn

-no solid surface: the second "giant" planet

-least dense of all the planets

-famous for ring system

-over 60 known moons

Uranus

-first planet discovered by telescope

-no solid surface: third "giant" planet, but significantly smaller that Jupiter or Saturn

-very cold: -350 degrees F

-over 25 known moons

Neptune

-predicted by mathematical calculation, then discovered (1846)

-similar in size to Uranus

-over a dozen known moons

-no solid surface: the last of the giant planets

Pluto

-five known moons

-orbit around the sun that is the more inclines and more eccentric than any of the 8 planets

-small than earth's moon

-discovered in 1930 as the 9th planets, reclassified as a dwarf planet in 2006

-visited by "New Horizons" spacecraft in July, 2015

greenhouse effect

a warming that results when the sun's light is trapped by an atmosphere

meteor

a flash of light observed when a small piece of solid matter enters Earth's atmosphere and burns up; "shooting star"

meteoroid

a particle or chunk of typically rocky or metallic material in space before any encounter with the Earth

meteroite

a portion of a meteoroid that survives passage through Earth's atmosphere and strikes the ground

comet

a small body of icy and dusty matter that orbits the sun