Astronomy 101

Mid Term Prep Unit 1-7

What is the difference between the horizon system and the equatorial coordinate system?

The horizon system is localized to the observer and uses two main elements, Altitude and Azimuth. The equatorial coordinate system uses the earth as its center projecting its equator,longitude and latitude and poles outward into the universe. The equatorial coordinate system uses a Celestial equator,celestial poles,right ascension(RA) and declination(DEC). The equatorial coordinate system is NOT observer dependent.

What is the horizon system?

An observer dependent method of measuring an objects location in the sky by using its altitude and azimuth.

What is the Equatorial coordinate system?

A non observer dependent method of pin pointing a celestial object. The ECS uses earth as its center projecting its equator,longitude,latitude and poles out into the sky.

Right ascension(RA)?

Longitude measurement of the Equatorial coordinate system.

Declination(DEC)?

Latitude measurement of the Equatorial coordinate system

Azimuth?

Distance around the horizon starting at 0degrees due north 90degrees east 180degress south and 270degree west. Used in the Horizon system

Cosmic address in order from home to country

home:Earth

neighborhood:Solar system

city:Milky way(galaxy)

state: Local group or virgo super cluster (galaxy cluster)

country: observable universe

Explain a day

The time it take earth to complete one full rotation on its axis which takes 24 hours.

Explain a month

A month is the time it takes the moon to complete one full orbit around earth. roughly 30days or 27 days for a sidereal month.

Explain a year

A year is the time it takes earth to complete one full orbit of the sun. Approx 365 days

What is a solar day?

The time from one noon to the next based on the suns position in the sky. Earth rotates on its axis while orbiting the sun,when earth finishes its rotation the sun isnt yet back in the same position because earth has moved along its orbit. earth must rotate an extra 1 degree to align the sun to noon. This takes 24 hours

What is a sidereal day?

The time it takes earth to complete one full rotation relative to the stars(23hours,56minutes,and 4 seconds). After one sidereal day the stars return to the same position in the sky, its a shorter day because no extra rotation is needed to account for earths orbital motion.

What are circumpolar stars?

Stars that never set below the horizon and are always visible on a clear nights. Only seen near the celestial poles north and south. Example: Polaris(the north star)

Define rise and set stars

Stars that rise in the east and set in the west each day. These stars follow the daily motion of rising and setting, driven by earths rotation.

Define never visible stars

Stars that remain below the horizon and cannot be seen from a specific latitude. Southern stars are hidden from northern observers and vice versa.

Why do earths seasons occur?

Earths season occur due to the tilt of its axis approximately 23.5 degrees relative to its orbit around the sun. As earth orbits the tilt causes different parts of the planet to receive varying amounts of sunlight throughout the year.

Explain summer

When the hemisphere tilted towards the sun gets more direct sunlight leading to longer days and higher temperatures

Explain winter

When the hemisphere tilted away from the sun receiving less direct sunlight resulting in shorter days and lower temperatures

Autumn and spring

When earths tilt cause moderate sunlight exposure.Days and nights are equal during these seasons.

What are constellations?

Officially recognized star patterns with fixed and defined boundaries, There are 88 constellations

What are Asterisms?

Informal star patterns usually made up of stars in multiple constellations.They lack an official boundaries

Whats the difference between Constellations and Asterisms?

constellations are officially recognized star patterns with defined boundaries and asterisms are informal star patterns usually made up of stars in one or more constellations. Asterisms lack official boundaries

what is the difference between a Solar and lunar eclipse?

Solar eclipse is when the moon passes between the sun and the earth. moons shadow is cast on earth. Lunar eclipse is when the earth passes between the sun and the moon, earths shadow is cast on the moon.

Why does the lunar eclipse last longer than a solar eclipse?

Because the earth is much larger than the moon its shadow is cast on the moon for a longer period of time.

Explain what a scientific model is

A model specifically used in science to explain,predict or understand natural phenomena.

What is an Abstract model? and give examples

NON physical representation often a concept or mathematical. examples: Newtons laws of motion,the theory of evolution,model of the atom

What is a concrete model? give examples

A physical representation Tangible. Examples: Scale model of the solar system, model of the human skeleton, dna double helix structure

What are some minimum requirements all scientific models must meet?

Must represent something in the natural world,Must make testable predictions,and must be limited.

Explain the geocentric model

Astronomical model placing the earth at the center of the universe with the sun,moon,planets and stars orbiting it.

Explain the heliocentric model

Astronomical model placing the sun at the center of the solar system with earth and other planets orbiting it.

Who proposed the heliocentric model?

Copernicus in the 16th century

Define a paradigm

Widely accepted framework of ideas and assumptions that shape scientific understanding and research.

Define a paradigm shift

A shift in a widely accepted framework of ideas due to new evidence.

Example of a shift in the paradigm

Geocentric model to heliocentric model

Name some evidence that helped with the geo/heliocentric shift

retrograde motion,Galileos discovery of venus phases and jupiters moons,Keplers laws of planetary motion based on tychos observations.

What are some strengths of the geocentric model

it could predict planetary motion well enough for practical uses like navigation and time keeping

what are some weaknesses of the Geocentric model

Struggled to explain retrograde motion and relied on complex epicycles, highly complex model

what are some strengths of the heliocentric model?

Accurately explains retrograde motion,matches telescopic evidence venus phases and jupiters moons. Simplicity,accuracy and predictive power.

Explains rise set motion of stars

explains zodiacs

where did revision of the geocentric model occur

Created in ancient greece revised in europe

Why was revision of the geocentric model needed?

Because it could not explain retrograde motion

Who developed the geocentric model and when

Aristotle but was later refined by ptolemy in the 2nd century

Who proposed the Heliocentric model

Nicolaus Copernicus challenged the geocentric model by proposing the heliocentric model in the 16th century

how did Galileo contribute to the heliocentric model and when

Galileo in the 17th century provided observational evidence using the telescope supporting the heliocentric model. his observations include the phases of venus and jupiters moons.

How and when did Johannes Kepler contribute to the idea of the heliocentric model?

Kepler in the 17th century refined the models with his laws of planetary motion based on tychos data introducing elliptical orbits.

How and when did Issac Newton contribute to the idea of the heliocentric model?

Newton in the late 17th century comes out with his laws of universal gravitation which provided a physical bases as to why planets orbit the sun cementing the heliocentric model

What struggles did galileo face

Put on house arrest for Heresy, His publications were banned

Kepler struggles

Faced religious and political difficulties, publications were banned

copernicus struggles

publications banned by the catholic church

What is an ellipse?

Oval shaped curve with two fixed points called FOCI

Key parts of an ellipse?

Semi major axis

Semi minor axis

Foci

What is eccentricity?

Its a measurement showing how from from a perfect circle an objects orbit is

E=0 is

Circular orbit

0<e<1 =

Ellipse

e=1

Parabola

e<1

hyperbolla

Keplers first law?

planets orbit elliptical paths with the sun located at one of the foci

Keplers 2nd law

Planets move faster when they are closer to the sun and slower when they are away

Keplers 3rd law

The square of a planets orbit P² is proportional to the cube of its semi major axis a³

write keplers 3rd law equation

P²=a³

P=

Orbital period(years)

a=

Semi major axis (au)

orbital velocity equation tells you what?

Speed required to maintain a circular orbit

Escape speed tells you what?

The minimum speed required to escape a gravitational field

Why do astronauts float?

Astronauts float due to freefall with a horizontal velocity moving them foward causing them to “miss” earth and stay in orbit.

Correct someone who says astronauts float due to no gravity

Astronauts “weightlessness or floating” is an effect of orbiting(freefalling with forward motion causing them to miss earth and stay in orbit) not absence of gravity

types of planets in our solar system

Terrestrial(Rocky inner planets like earth,mars,mercury and venus)

Giants(outer planets mainly composed of gas and ice,Jupiter,saturn,uranus and neptune)

what are the 3 small body populations?

Asteroid belt

Kuiper belt

Oort cloud

how many planets in our solar system?

8

Define a planet using IAUs definition

A celestial body that

orbits the sun

Is massive enough to be Spherical

Has cleared its orbital path of debris

Define a dwarf planet by IAU standards

Orbits the sun

is nearly spherical

is not a moon

has not cleared its orbital path

What is an asteroid

A rocky metallic body mostly found in the asteroid belt

What is a comet

An icy body that releases gas and dust when near sun

what are meteoroids?

small particles from comets and asteroids

What is stage 0 of the core accretion theory?

Solar nebula, the starting point a massive cloud of gas and dust containing the raw ingredients to create a star and solar system

What is stage 1 of the core accretion theory?

Cloud collapse, Solar nebula collapses under its own gravity resulting in the cloud flattening into a spinning disk. forming two main regions the protostar and the protoplanetary disk

What is stage 2 of the core accretion theory?

Condensation,Where gases turn into solids due to cooling in space.

Where does ice condense in the protoplanetary disk?

beyond the iceline

What is the Ice line?

An imaginary boundary where temperatures allow water ice to condense

Do dense materials condense near the center at high temperatures or near outer regions with low temperatures?

Dense materials such as Rock and metals condense near the center at high temperatures.

What is stage 3 of the core accretion theory?

Accretion, The process where solid particles collide and stick together growing larger over time

Accretion level 1

Grains to pebbles driven by static

Accretion level 2

Pebbles to planetismals Pebbles aggregate to planetismals believed to be driven by friction with gas

Accretion level 3

Planetismals to planets, planetismals collide with each other, Gravity driven

Rocky planets form from how many levels of accretion?

3 levels, planets to small to capture gases

Accretion level 4

Planets core reaches critical mass and captures gases into its atmosphere.

Giant planets form where and how many accretion levels does it require

Forms outside the iceline, with 4 accretion levels. large core able to capture gases into its atmosphere

which planets have high densities Giant or rocky planets?

Rocky since they are mostly made up of heavier materials like rock and metals

True or false

All planets exert the gravity on each other force is the same for both but effect is not

What is stage 5 of the Core accretion theory?

Disk dispersion, the end of planet formation. Proto star becomes a star and releases a stream of particles blowing all the remaining gas away

A protostar becomes a star when?

When the protostar reaches critical mass and begins hydrogen fusion

what is solar wind?

A stream of particles released from a star

where are asteroids found?

asteroid belt

where are comets found

Kuiper belt or Oort cloud

Difference between asteroid and comet

Asteroid made up of mainly metal and rock, has no tail

Comet made up of mostly water ice,rock and dust, has a tail

where are short period comets found

Kuiperbelt

Where are long period comets found

Oort cloud

What is the Oort cloud?

Theoretical spherical cloud of icy objects surrounding the solar system.

why do we believe the Oort cloud exists?

Mainly due to the behavior of long period comets, they approach from all directions and are highly elliptical