what does modern science offer answers to?

fundamental questions about the universe and our place within it

what do we know about the universe according to modern science?

basic content and scale of the universe

ages of Earth and the universe

scale of the universe

size and extent of the universe

- includes basic content and structure

history of the universe

development and changes in universe from its beginning to the present

star

a large, glowing ball of charged gas that generates heat and light through nuclear fusion in its core

"nuclear furnace"

solar / stellar system

a star and all the materials that orbit it -- including planets and moons

Milky Way galaxy

- our galaxy

- the band of light we see in the sky when we look into the plane of our galaxy

galaxy

- great "island" of stars in space

- all held together by gravity

- orbit a common center

local group

group of about 40 galaxies to which Milky Way galaxy belongs

- one of the two largest among them is Milky Way

galaxy clusters

collection of a few dozen or more galaxies bound together by gravity

- smaller collections called groups

superclusters

clusters of galaxy clusters

largest known structures in the universe

Laniakea

local supercluster

translates to "immense heaven"

light year & kilometers conversion

1 light-year = 9.46 trillion km

astronomical unit

average distance (semimajor axis) from Earth to the Sun

~93 million miles (150 million kilometers)

light year

distance that light can travel in one year

approx. 10 trillion kilometers

the farther away we look in the distance...

the further back we look in time

structure of galaxies and galaxy clusters

arranged in giant chains and sheets with huge voids between them

planet

- moderately large object that orbits a star

- shines primarily by reflected light (from its star)

may be rocky, icy, or gaseous in composition

moon

object that orbits a planet

satellite

any object orbiting another object

asteroid

relatively small & rocky object that orbits a star

comet

relatively small & ice rich object that orbits a star

small solar system body

asteroid, comet, or other object that orbits a star

too small to qualify as a planet or dwarf planet

universe

sum total of all matter and energy

- all galaxies and everything in between them

observable universe

portion of the entire universe that can be seen from Earth

exoplanet

planets in other solar systems around other stars

nebula

interstellar cloud of gas and dust

how stars and stellar systems are formed

TNOs

dwarf planets

trans-neptunian objects

rotation

spinning of an object around its axis

orbit (revolution)

orbital motion of one object around another due to gravity

measured age of the universe

14 billion years

boundary of our observable universe

expansion (of the universe)

increase in average distance between galaxies as time progresses

levels of the universe

earth -> inner solar system -> outer solar system -> closest stars -> Milky Way -> local group -> laniakea -> local superclusters -> observable universe

solar day

time for the sun to return to the meridian

avg. 24 hours

sidereal day

time for a distant star to return to the meridian after a rotation

23 hours, 56 minutes, 4 seconds

*Earth's TRUE rotation rate*

why are the solar day and sidereal day different?

Earth also has to revolve around the Sun in our orbit and have to turn a tiny bit more to face the sun again

north celestial pole

directly above Earth's North Pole

ecliptic

the Sun's apparent annual path around the celestial sphere

geocentric universe

ancient belief that universe is "Earth-centered"

ie. Earth is center of universe and all other celestial bodies orbit around Earth

ecliptic plane

Earth's orbital path

celestial sphere

puts stars and constellations onto an imaginary sphere around us

*not realistic, just how it appears to us from Earth

earth moves from

west -> east

what direction do the sun, moon, planets, and stars all appear to rise and set?

east -> west

what direction does earth spin?

counterclockwise (when viewed from above the North Pole)

how much is earth's axis tilted?

23.5 degrees (from a line perpendicular to the ecliptic plane)

earths axis remains pointed...

in the same direction in space throughout the year

earths orbit moves...

in the same counterclockwise direction as its rotation

earth's axis points toward the star...

Polaris

- the North Star, always found in a direction of due north

earths distance from the sun...

varies slightly over the course of the each year

earth orbits the sun in the same direction that...

it rotates on its axis

local solar neighborhood

region of the Sun and nearby stars

dark matter

matter inferred to exist from gravitational effects, but no light has been detected

- dominates total mass of the universe

dark energy

energy that could be causing the expansion of the universe to accelerate

virtually every galaxy outside the local group is moving...

away from us

the more distant the galaxy...

the faster it appears to be racing away

raisin cake

analogy to explain expansion of universe

expansion of cake causes raisins to move away from local raisin -- more distant raisins move away faster

distant galaxies are all moving away from us, with more distant ones moving faster...

indicating that we live in an expanding universe

how do observations of expansion allow us to measure the age of the universe?

faster the rate of expansion, the more quickly galaxies reach their current position -- therefore the younger the universe must be

problems with raisin cake analogy

- cake has center and edges; same may not be true for the universe ( no place is more central than any other place)

-can't see galaxies moving apart with time

Doppler shifts

way of measuring speeds of galaxies via spreading their light into these spectra

constellations

region of the night sky with well-defined borders

familiar star patterns help us find them

south celestial pole

point directly over Earth's South Pole

celestial equator

projection of Earth's equator into space

- makes a complete circle around the celestial sphere

Milky Way

band of light that circles around celestial sphere

- traces our galaxy's disk of stars-- the galactic plane-- as it appears from our location within the galaxy

local sky

sky as seen from wherever you happen to be standing

horizon

boundary between earth and sky

zenith

point directly overhead (in sky)

meridian

imaginary half-circle stretching from horizon due south, through the zenith, to the horizon due north

direction

one of two coordinates needed to pinpoint an object in the local sky

altitude

(above horizon) the angular distance between the horizon and an object in the sky

declination

north-south location on sky (like latitude)

(degrees, arcminutes, arcseconds)

right ascension

east-west location on sky (like longitude)

hours, minutes, seconds

angular size

(of an object) the angle it appears to span in your field of view

- also depends on distance

angular distance

(between objects) angle that appears to separate them

celestial sphere appears to rotate...

east to west

circumpolar

star that always remains above the horizon for a particular latitude

stars near south celestial pole...

never rise above horizon at all

0 point for right ascension

where the sun crosses the celestial equator on the march equinox

the farther away an object is...

the smaller its angular size

stars near North Pole are...

circumpolar, meaning that they remain perpetually above the horizon, circling (counterclockwise) around the north celestial pole each day

stars near south celestial pole...

never rise above the horizon at all

others stars have daily circles that are...

partly above the horizon & partly below

why they appear to rise in the east and set in the west

positive declination

north of the equator

negative declination

south of the equator

relationship between angular size (in degrees), physical size, and distance

angular size/360 degrees = physical size / 2pi x distance

does the sky vary with latitude or longitude?

latitude

the altitude of the celestial pole in your sky =

your latitude

the constellations visible at a particular time of night...

change as we orbit the Sun

Earth's axis points in the same direction all year round, which means...

its orientation relative to the Sun changes as Earth orbits the Sun

If Earth did not have an axis tilt...

we would NOT have seasons

summer solstice (June solstice)

occurs around June 21st

moment when the Northern Hemisphere is tipped most directly toward the Sun

- receives the most direct sunlight

winter solstice (December solstice)

occurs around December 21st

the moment when the Northern Hemisphere receives the least direct sunlight

spring/ vernal equinox (March equinox)

Northern Hemisphere goes from being tipped slightly away from the Sun to being tipped slightly toward the sun

fall/ autumnal equinox (September equinox)

moment when the Northern Hemisphere first starts to be tipped away from the sun

we use equinoxes and solstices to mark...

the progression of the seasons

equinox

sun rises precisely due east and sets precisely due west

solstice

Sun rises and sets farthest to the north of due east and due west

high latitudes have...

more extreme seasons

precession

gradual wobble that alters the orientation of Earth's axis in space

the tilt of Earth's axis remains close to 23.5 degrees, but...

the direction the axis points in space changes slowly with the 26,000-year cycle of precession

what causes precession?

gravity's effect on a tilted, rotating object

lunar phases

Moon's appearance in the sky changes as its position relative to the sun changes

the sun comes from essentially the same direction...

all along the Moon's orbit

moon phase takeaways

- we always see the same side of the moon facing Earth

- as moon orbits Earth, we see different combinations of its bright and dark faces

the phase of the moon depends on...

its position relative to the Sun as it orbits Earth

the moon's phase affects not only its appearance but also...

its rise and set times

new moon

rises and sets with sun

waning crescent

rise: before dawn

highest: mid-morning

set: mid-afternoon

third quarter

rise: midnight