Intro to Astronomy: Ch.1-5 Review

Astronomy

is the study of the world beyond our own.

Astrophysics

is the astronomical phenomena explained by using physics.

Star

the universe’s basic building block: a highly compressed ball of mostly hydrogen and helium gas.

Globular Cluster

a ball of one to ten million stars, or occasionally more.

Galaxy

a large grouping of 100 billion stars in spherical or football (elliptical) or disk (spiral) shapes; Milky Way is our own spiral galaxy and Andromeda Galaxy is the nearest large galaxy, a spiral.

Clusters of Galaxies

a grouping of tens to thousands of galaxies.

Local Group

the local cluster of about 30-50 galaxies containing our own galaxy, andromeda and many small ones.

Superclusters

clusters of clusters of galaxies.

Voids

the universe contains vast empty spaces between clusters of galaxies.

Cosmology

is the study of the large-scale make-up and origin of the Universe.

Speed of Light ( c )

is very large but finite speed of travel of light: c = 3.0 × 10^8 m/s = 300,000 km/s (units of meters or kilometers per second)

Astronomical Lengths—Astronomical Unit (AU)

distance from Earth to Sun.

Light-Year (ly)

distance light travels in 1 year. ( = 63,000 AU )

Parsec (pc)

a unit for expressing distance to stars and galaxies, this unit is approximately 3.26 (ly).

Angular Measure—Degree

there are 360 Degrees in one revolution.

Minutes of Arc (arcminutes)

there are 60 arcminutes in 1 degree.

Seconds of Arc (arcseconds)

there are 60 arcseconds in one arcminute.

Angular (apparent) size

size in degrees of an object seen: AS= 57.3 Degrees x (true object size) / (distance to object)

True or Physical Size

the real size of an object measured in some length unit.

Constellation

grouping of stars in the sky representing an object, with names from ancient mythology (for example, Orion, Ursa Major, Taurus).

Celestial Sphere (CS)

the spherical projection (picture) on the sky used to represent astronomical objects.

Horizon

the perimeter of the plane on which one stands.

Zenith

the high point of the sky above you.

Meridian

the great circle passing through the zenith.

North Celestial Pole

the point in the sky where Earth’s rotation axis points, the star Polaris marks it.

Celestial Equator

Earth’s equator extended onto the celestial sphere.

Ecliptic

Sun’s path across the sky (a great circle), marked on the celestial sphere and tilted at 23.5 Degrees to the celestial equator.

Right Ascension

like longitude on Earth, a measure (in time) of the location of an object on the CS.

Law of Gravitation

the force of attraction Fg between two masses at a distance d: fg = G M1 M2 / d2 , G is the Gravitational constant.

Weight

is the force of gravity of Earth acting on an object; works also on another planet.

Pressure

the action of a force distributed over area A of application: P = F / A

Radius ( r )

the distance from the center of rotation.

Angular Momentum ( L )

measures an object’s rotation by its speed v, radius of orbit r, and mass m: L = r m v

Conversation of Angular Momentum

L is conserved, that is, not lost or gained.

Eratosthenes

found Earth’s size using the change in the length of shadows from place to place.

Parallax

the apparent visual shift of a nearby object against a distant background when moving sideways.

Ptolemy’s Geocentric Model

SS model where planets move on epicycles with Earth at center.

Copernicus’ Heliocentric Model

SS model with Sun at center; planets travel along simple circles.

Tycho Brahe

advanced the accuracy of star and planet position measurements by a factor of six, namely, from 0.05 degrees to 0.0083 degrees = 0.5 arcmin.

Kepler’s Laws (3) of planetary motion

planets move along ellipses (ovals), the speed varies near to and far from the Sun; P2 = a3, with P a planet’s period of orbit in years and a the average of the planet from the Sun in AU.

Light Rays

light collimated into thin beams or rays.

Reflection, Refraction

light rays bounce off (reflect) a polished surface or they bend (refract) when passing into another transparent medium.

Lenses

disks of transparent material, rounded inward or outward, that use refraction to focus (bend) light.

Telescope

instrument to observe distant objects (Galileo, 1610) with an objective (lens or mirror of diameter D) to gather light from an object and an eyepiece to focus and magnify the image.

Electromagnetic (EM) spectrum

gamma-rays, x-rays, UV light, visible light, infrared radiation, radio waves.

Refractor

a telescope using only lenses.

Reflector

a telescope using a mirror as objective to gather the light.

Magnification

the overall increase in angular size of the image seen through a telescope.

Resolving Power

smallest angular separation a telescope can distinguish: RP = 57 x λ / (objective size), where λ is the wavelength in meters.

• λ - is the symbol for wavelength, which is called Lambda, a Greek letter.

Light-Gathering Power

area of the light collecting of objective of a telescope: LGP = constant x (diameter of objective)2

Declination

like latitude on Earth, the second measures (in degrees) of an object’s location on the CS.

Retrograde Motion

the temporary backward motion of a planet across the sky.

Seasons

the cycle of heating and cooling on Earth due to the changing intensity of sunlight from the 23.5 degree tilt of Earth’s rotation axis relative to the plane of its orbit.

Moon Phases

are the apparent shapes of the sunlit portion of the Moon as seen from Earth, caused by the Moon’s orbit around Earth changing the amount of its illuminated surface that we can see.

New Moon

The dark moon.

First-Quarter Moon

a half moon that brights on the right side.

Third-Quarter Moon

a half moon that brights on the left side.

Full Moon

bright complete moon.

Eclipses

one object passes through another’s shadow.

Lunar Eclipse

The moon passes through earth’s shadow.

Solar Eclipse

The earth passes through moon’s shadow.

Umbra

the dark inner, shadows of an object.

Penumbra

the less dark, outer shadows of an object.

Total Eclipse

is when object is in the umbra. completely blocks the whole thing.

Partial Eclipse

when the object is in penumbra, covers a portion of the thing.

Power of Ten notation (10 n)

use 10 multiplied n times to represent 1,00…00 within n zeros or 10 -n for 1/10 n = one divided by 10 n.

Order-of-magnitude

estimating the size of something in powers of ten.

reasoning—Occam’s razor (Law of Parsimony)

the simplest explanation is likely the correct one. involve with deduction and induction.

Deduction (deductive reasoning)

reasoning from the general to the particular; calculation using a law.

Induction (inductive reasoning)

reasoning from particular facts to obtain a general relation (law).

Inference

is the conclusion of a deductive argument.

Science

observations lead to a hypothesis and a prediction, then an expirement provides data that either verifies or falsifies the hypothesis.

Observation Data

mostly qualitative features noted about some natural phenomenon.

Experiment Data

a controlled observation of a hypothesis with quantitative measurements or data.

Hypothesis

is a proposed relationship among physical quantities about how nature works.

Theory

a set of verified hypotheses.

Model

a representation of a theory allowing numerical computation.

Verifying and Falsifying

showing from experiment that a hypothesis is correct or is wrong.

Inertia

the resistance to change in an object’s motion measured by an object’s mass.

Speed ( v )

the measure of the motion (distance covered per given time) of an object in m/s (meters per second)

Acceleration ( a )

the change in an object’s speed versus time in units of m/s2

Force ( F )

a push or a pull or gravity acting on an object, causing it to move.

Mass ( m or M )

measures the quantity of matter.

Newton’s Three Laws of Motion

1. The law of Inertia

2. The law of acceleration, F = m a

3. The law of action-reaction

Twinkle Effect

a main limiting factor of ground-based telescopes caused by the atmospheric distortion of images.

Adaptive Optics

“correction” of twinkle effect by comparison to single star image.

How is Earth Unique?

It’s the only planet in the solar system with the next five traits.

1. Life

2. Liquid Water

3. Oxygen

4. Plate Tectonics

5. Magnetic Field

Plate Tectonics

Earth’s crust consist of independent pieces they move and collide.

Atmospheric Oxygen

A planet with significant oxygen in its atmosphere.

Surface Liquid Water

a planet where temperature and pressure allow surface water to be in liquid form, helping the development of life.

Climate Stability

atmospheric conditions are relatively stable over time.

Life

In the solar system, Earth is the only world known to have life, which is both abundant and diverse.

Carbon Dioxide (CO2)

the most common gas released by volcanos on a planet; on earth, it gets locked up into rocks in the oceans after rains carry it there.

Global Warming

the trapping of heat in the atmospheric due to extra manmade CO2 or other greenhouse gases.

Ozone Hole

destruction of earth’s upper atmospheric ozone ( O3 ) layer by chlorine released from chlorofluorocarbons (CFCs) by UV Radiation.

Moon

one of the largest planet satellites (moons) of any planet in SS; heavily cratered; no liquid or atmosphere; now thought to originate from an early major impact on Earth which squished out material that later reformed as the Moon.

Inner, Terrestrial Planets

Their make-ups are metallic/rocky with average densities of 5 g/cm3 (water’s is 1 g/cm3) and consisting of a solid-inner and liquid-outer core of mostly iron, a liquid rocky middle layer (mantle), and thin rigid crust (lithosphere).

Mercury

mostly, a large iron core due to early large impact; cratered much like the moon; few lowland (seas) or highland flat areas; hot, due to Sun’s closeness; no atmosphere; small magnetic field; 1/3 larger than Moon; no moon.

Venus

size of Earth (Earth’s twin); dense atmosphere of carbon dioxide (CO2) with caustic sulfur dioxide (SO2) clouds; very hot (~450 Degrees Celsius) due to runaway greenhouse-effect trapping of infrared heat; enormous pressure (90 times Earth’s); no moons or magnetic field; some high mountains; mapped by radar; no moon.

Earth

dense atmosphere with oxygen (O2) ; much liquid water (H2O); moving crustal plates (plate tectonics); originated/sustains much life; long-term stable climate; strong magnetic field; large moon.