Astronomy #1 Exam Review

Scientific Notations

• 10^0= 1

• 10^1=10 (1 zero)

• 10²=100 (2 zeros)

• 5.3 × 10³= 5,300

• 8.9 × 10^4= 89,000

• 10^-1 = 0.1

• 10^-2= 0.01

• 2.1 × 10^-2= 0.021

Orders of magnitude

The numbers of powers of 10 that two things differ by (The orders of magnitude that separate them)

• EX: two orders of magnitude = 10²

  • EX: The sun is 100 times larger than the earth, so it is 2 orders of magnitude larger than the earth

What are Quasars?

Extremely distant black holes shining brighter than MOST GALAXIES, but SMALLER than our solar system!

• Looks like a star, but there’s a bunch of stars within it

• brighter b/c it has a lot of gas supply

• The easiest star to map out

What are superclusters?

A lot of galaxies near each other

Void

regions with very few galaxies

Naked eye planets

Planets you can see without a telescope

What is Orion

Roughly 3000 stars are visible at once

• what made months a thing, 30 days long, 360 min in an hour, 360 sec in a minute, ect.

What are the outermost limits of the Universe?

More than 40 billion light years away

When does the first quarter moon rise and set

Rises at noon

Sets at midnight

when does the full moon rise/set

rises sunset

sets sunrise

Earth is…

• light MINUTES away from the nearest PLANETS

• light YEARS from the nearest STARS

• MILLIONS OF LIGHT YEARS from the nearest large GALAXIES

when does the third quarter moon rise and set

rises at midnight

sets at noon

When we look at distant objects, how do we see them?

• As they were when the light left them.

• Traveling far in space means traveling back in time.

What are constellations?

The patterns of stars that stay the same

• Stars being grouped because they are in about the same direction (NOT PHYSICAL)

• 88 regions of the sky

  • 48 of them are defined by ancient greeks

• Don’t really change relationships to each other

Zenith

The point directly overhead (so if you were to look straight up)

Horizon

The lowest part of the sky you can see; just above the earth’s surface

• You can see anything above it, not below

• So, we always see 50% of celestials, the other 50% is below the horizon

North/ South Celestial poles

The points on the celestial sphere where it intersects the Earth’s axis projected outward

• The earth rotates on this line, and the sphere rotates in the opposite direction but around the same imaginary line

  • North pole, South pole

Celestial equator

The ring on the celestial sphere where it meets Earth’s equator, projected outward

• Just like the Earth has an equator, we can project the equator of the earth till in meets our celestial equator.

• Could be overhead at some point if you live on the Earth’s equator

How do stars move

East to West

• They rise a 4 minutes earlier each night

Circumpolar stars

• Stars near the North Celestial Pole (Polaris)

• Travel in a circle around the pole

• stay above the horizon

Ecliptic

the current path of the sun from EARTHS POV

• It takes 1 year for the Earth to go around the sun

• titled 23.5 degrees

• the reason for the Earth’s changing seasons

The sun’s apparent path

• Always RISES towards the EAST and SETS in the WEST

• Due to Earth’s tilt, it gets HIGHER in the sky at noon in the SUMMER, lower in the sky at winter

  • Closest overhead at noon on the summer solstice

Polaris movement

• The pole doesn’t move

• So, The pole star BARELY moves

• WHY?

  • Since earth rotates on an axis that runs through North and South poles, if you were to draw a straight line out it points at Polaris.

How stars near polaris move

• circumpolar stars circle the pole

• The stars move in an counterclockwise

• They don’t rise or set because they are near the pole

Annual changes in constellations

• Different constellations are on the RIGHT side of Earth at different times of the year

• Stars rise 4 MINUTES earlier each night

• FIGURES ARE NOT TO SCALE

Describe in what direction from us the Sun, Moon, planets and most stars rise and set, and why they do so

• Rise in the east and set in the west BECAUSE the Earth spins from west to east on its axis (Counterclockwise)

• One full turn takes 24 hours

What do the motions of Earth correspond to (day and year)

• Rotates (spins) on its axis around the sun

• Takes 24 hours to do one full spin; 365 days (1 year) to do one full trip around the sun

• This is what creates day and night bc the side facing the sun experiences daytime, while the side turned away experiences night

• The 23.5 degrees tilt of the Earth creates our CHANGING SEASONS b/c different parts of the planet receive more or less direct sunlight throughout the journey.

What are the two causes of seasons?

The Earths tilt, and directness of sunlight varies over the year

• The Ecliptic (plane of earth’s orbit) is tilted at 23.5 degrees!

• When it is tilted TOWARDS the sun, its SUMMER and when the tilt is AWAY from the sun, its WINTER

  • The sun is closest overhead at noon on the summer solstice, lower in the sky during the winter

  • we get less sun when the sun is lower in the sky

  • So, not only do we get less hours of daylight in the winter, but the light we get is also less intense.

• When it is summer in the northern hemisphere, it is summer in the southern hemisphere

What would happen if Earth didn’t have a tilt?

Latitude alone would determine how much sun you get. So, the equator would get the most sunlight.

What causes the phases of the moon?

• Due to us only seeing part of the sunlit moon

• Depends on its position compared to the earth and sun

• There is a daytime and nighttime for the moon

• New moon, full moon, quarter moon

New Moon

Completely dark.

• It’s not that its not getting sunlight, but the side that IS, is not facing us.

• Rises and sets at the same time as the sun

Full moon

The side we see is entirely lit up

• Opposite the sun and sky, so sets when the full moon rises

quarter moon

50% is lit up, 50% is dark

• Rises at noon and sets at midnight.

When do eclipses occur?

When the Earth, Moon (Tilted 5 degrees), and Sun form a straight line

• The moon’s shadow will cross the earth OR the Earth’s shadow will cross the moon

• Both have to happen perfectly

RARE!!!

Lunar Eclipse

• When the EARTH is between the Moon And Sun

• The moon has to be BEHIND the earth

• Full moon going in AND coming out

• The moon becomes dark b/c its in earth’s shadow

Blood moon: even though it’s in the earth’s shadow, some light still comes through

Solar Eclipse

Moon is perfectly aligned between earth and sun

• the moon has to be BETWEEN the earth and sun

• The Sun goes dark

• Can be Partial, TOTAL, or annual

Total Solar eclipse

• denser shadow

• The moon will look to be the same size in the sky as the sun (just close/big enough to block the sun barely)

Corona

the outer atmosphere of the sun

What phase of the moon must the solar eclipse happen during?

THE NEW MOON

What phase of the moon must the lunar eclipse happen during?

FULL MOON

What are 2 things light consists of?

Wave and Particle

Wave

moving pattern, carries energy

Particle

Fixed pieces, carries energy

• light can be absorbed in fixed amounts (particles) so not half absorbed

Electric force

Attracts/repels ELECTRICALLY CHARGED objects

• Two positive/negatives: pushes apart

• One positive, one negative: it attracts

• Responsible for static shocks/electricity

• Can be both positive or negative, or you can have just a positive charge or just a negative charge

Magnetic Forces

Attracts/ repels MAGNETIC POLES (North pole & South pole)

• what causes compasses to work

• Two north/south poles: pushes each other apart

• one north, one south: attracts

• if you have a north pole you HAVE a south pole (they always coming together)

  • north pole always points to the south pole

What do electric & magnetic forces tell you?

The direction and strength

• if it’s closer, its stronger

If you change the electric field what must you do?

Change the magnetic field

what actually makes up light?

Electromagnetic Waves

• LIGHT IS ELECTROMAGNETIC RADIATION

Electromagnetic wave

A wave occuring in the electric and magnetic fields

• always moves at the same speed

• all of our technology relies on this

Electromagnetic waves in astronomy (stars)

Stars are made of protons, electrons, and neutrons

• they’re really hot, so the electrons get stripped from the protons, and electric charges are flying around

• This is what makes telescopes detect light traveling to earth

Radiation

when energy travels from one place to another without a direct contact between the two

What are basic properties of a wave?

• wavelength

• frequency

• speed

• amplitude

Wavelength

The DISTANCE between two peaks

Frequency

how long does it take to get from peak to peak

• measured in Hertz (Hz)

  • hertz: number of peaks per second

speed of a wave

How fast the peak is moving.

• speed = wavelength/period

• speed = wavelength x frequency

• light can cancel light

speed of light or light waves

C ∝ wavelength x frequency FOR ANY TYPE OF LIGHT

• wavelength∝ c/frequency

• wavelength ∝ 1/frequency

• frequency ∝1/wavelength

if the wavelength is small/big, what does that say about the frequency?

• small= frequency big

• large= frequency small

What is visible light

• the light our eyes can see

• red, orange, yellow, green, blue purple

• White light is NOT A THING!! its always made up of different colors

Red

Has the longest wavelength light

• Although has a shorter frequency and enegry

Blue

Has the shortest wavelength light

• BUT larger frequency and energy

Spectrum

when we split light into different components

• so the range of all wavelengths of light is the ELECTROMAGNETiC SPECTRUM

Proportionality

• MULTIPLYING & DIVIDING, no adding or subtracting

• whatever you do to change the right hand side, you have to do to the right hand side

Which one has the highest frequnecy, which one has the lowest?

Highest: Gamma rays

Lowest: Radio waves

Longer wavelengths causes what to the frequency?

smaller frequency

E ∝ F (frequency)

HIGHER FREQUENCY = HIGHER ENERGY

• one of the ways light acts as a particle

Everything in the Universe has what 2 things?

A wave and particle nature

The Inverse-Square Law

If we have a source of light giving light in every direction, then the amount of light that goes through a sphere per second HAS TO BE THE SAME no matter the size

• the amount of light per sq meter determines how much bright light we see

  • EX: a street light is brighter if it’s closer

• Intensity of light ∝ energy output per time / distance²

  • more distance = less intensity

  • closer distance = more intensity

  • INTENSITY DROPS FASTER THAN DISTANCE DOES.

Surface area of a sphere

4nr²

Thermal Radiation

• ALL objects in the universe emit radiation (light)

• Hotter outside: the particles in the air are moving faster and have more energy

The Kelvin temperature scale

• 0k means theres no random (thermal) motion

  • ABSOLUTE Zero

Ideal thermal emitter (BLACKBODY RADIATION

• has to be TOTALLY OPAQUE (can’t see through it)

• Absorbs all light hitting it determined ONLY by temperature

• EX: the sun

• Shorter wavelengths have more intensity

• none of us are observing every wavelength of light or we would be black

peak wavelength

the wavelength where the intensity of light is the highest

• so, where the curve is the highest

Wien’s law

Tells us that if an object is HOTTER, the peak wavelength will be SHORTER

λ peak (peak wavelength) ∝ 1/T

• T is temperature in K

• When T is bigger, wavelength is smaller

What color are hot objects that PEAK at SHORT wavelengths

blue

What color are cold objects that PEAK at Long wavelengths

Red

Stefan’s law

Adding up all the energy at every possible wavelength to get the total energy is PROPORTIONAL to the fourth power of temperature

• So, intensity ∝ T^4 , if t is measured in k