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CSU / Astronomy / AA / What is the difference between astrology and astronomy?

What is the difference between astrology and astronomy?

What is the difference between astrology and astronomy?


School: Colorado State University
Department: Astronomy
Course: Introduction to Astronomy (GT-SC2)
Term: Fall 2019
Tags: astronomy, copernicus, kepler, galileo, lawsofmotion, moon, sun, orbit, planets, and grapefruit
Cost: 50
Name: AA 100 Unit 1 Study Guide
Description: Everything from the study outlines on the powerpoints!
Uploaded: 09/23/2019
10 Pages 64 Views 12 Unlocks

Unit 1 Study Guide

What is the difference between astrology and astronomy?

1.1-1.3, 2.3

Science vs. pseudoscience



Explanations based on natural causes

Vague/misleading language

Occam’s razor - if two models agree equally well w/ outcomes, use the simpler model

Untestable claims

Falsifiability - has the capacity to be proven wrong

Lack of self-correction

Difference between astrology and astronomy

- Used to be the same practice until ~ 17th century

- Tycho, Kepler, Galileo all astrologists/astronomers

What is a scale model?

- Connection to astrology was good for astronomy b/c it helped further astronomical research

Ecliptic vs. Zodiac

- Ecliptic is the apparent orbital path in the sky that the sun and other celestial bodies are confined to over the course of a year We also discuss several other topics like How can we define the marketing mix?

- Ecliptic passes through all 13 of the zodiac constellations


Scale Models

Help us to visualize our place/other things in the universe

Seeing through time

Light travels at the speed of light. Because we don’t receive the light immediately, we see light from the past. Therefore, when light reaches us, we are seeing things how they looked in the past.

“We are Stardust”

Almost everything in our universe (including humans) is made out of elements from dead stars.

What are the seasons around the globe?

Don't forget about the age old question of Which cells produce surfactant in the alveoli?

Astronomical Units and Light Years

Astronomical Units (AU)

Light Years

Average distance from the earth to the sun

Distance that light can travel in one year 300,000 km/sec

1 AU = ~8 minutes

Used b/c information comes through light

Light Year distance from __ to Earth

Moon - 1 second

Sun - 8 min

Sirius - 8 years

2.1, 4.1

Constellations vs. Asterisms

- Constellations are sections of the sky (like states) that contain groups of stars; asterisms are notable star patterns within constellations (ex: big dipper).

- Some asterisms cross constellation borders

- Ptolemy’s Almagest recorded 88 constellations

Using stars for navigation

Polaris is very near the North Celestial Pole, so Polaris’s altitude from a certain location is equal to the North latitude of that location

Changing universe Don't forget about the age old question of What happened to king phillip's war?

- Order of things:

Big bang → only hydrogen → hydrogen & helium → 1st galaxies → now

- Stars recycle and create elements throughout life cycle

- Most elements made by merging neutron stars, others by exploding stars and dying low mass stars

Altitude/azimuth vs. equatorial coordinates

altitude/azimuth - height above the horizon/NSEW direction; used for local coordinates Equatorial coordinates - horizontal/vertical coordinates on the celestial sphere; stay the same globally


Cause of seasons (two properties)

- Earth’s tilt on its axis causes the seasons because it alters the directness of sunlight in the hemispheres as well as length of exposure to light

- Hotter in summer because hemisphere tilted towards sun = more direct sunlight and longer days - Colder in winter because hemisphere tilted away from sun = angled sunlight and shorter days - Because of the difference in the angle that sunlight hits the earth, seasons can be tracked using the length of the sun’s shadow on a stationary object

Marking the progression of seasons

- Solstices and equinoxes mark the beginning (first day) of each season

- Fall - autumnal equinox; spring - vernal equinox

- both equinoxes have ~ 12 hours daylight, 12 hours nighttime If you want to learn more check out What is intelligence quotient/iq?

- Winter - winter solstice; shortest day of the year

- Summer - summer solstice; longest day of the year

Seasons around the globe

- Seasons at the Poles

- Always cold; seasons are the difference between 24 hours daylight (summer) and 24 hours nighttime (winter)

- Seasons in the tropics (between tropics of cancer & capricorn -- near the equator) - Always hot; seasons are the difference between rainy & dry

- Mid-latitudes = four seasons with varying weather

Seasons on different planets

- Less extreme tilt = less extreme difference in seasons

- More extreme tilt = extreme difference in seasons


Phases of the Moon

Moon phases caused by the moon’s angle in relation to the earth and sun, NOT the earth’s shadow on the moon! We also discuss several other topics like When did ivy lee open his pr firm?

- Phases (in order): New, Waxing Crescent, First Quarter, Waxing Gibbous, Full, Waning Gibbous, Third Quarter, Waning Crescent

- Waxing phases = growing phases; moon is lit on the right side

- Waning phases = shrinking phases; moon lit on the left side

- Complete phase cycle = 29.5 days (synodic month)

- ~Two phases per week

Wandering Moon

- Moves across the sky at .5 degrees per hour (to the east)

- Diameter of moon = ~.5 degrees; moon moves one moon diameter across the sky each hour

Moonrise/Moonset (phases during day only, night only)

- rise/set times depend on the phase

- New moon - rises sunrise, sets sunset; only “visible” during the day

- Full moon - rises sunset, sets sunrise; only visible at night We also discuss several other topics like Who is theodor adorno?

Estimating moonrise/set times (using worksheet from class):

- Shade moon to what it looks like overhead from earth in any given phase

- Determine where the sun would need to be to create that shading

- Determine time that corresponds to that sun - that’s the moon phase’s meridian crossing - Moonrise is 6 hours before that meridian, set is 6 hours after

Moon’s rotation

Moon revolves at same speed that it orbits earth, keeping the same side facing Earth at all times - Only one side of the moon ever faces the earth = moon is tidally locked

Sidereal vs. Synodic months

- Sidereal month is the time it takes the moon to orbit the earth (27.3 days)

- Period is measured by the moon’s position in relation to other celestial objects - Synodic month is the time it takes the moon to go through a full phase cycle (29.5 days) - Measured by appearance from Earth

- Discrepancy between sidereal/synodic month lengths due to Earth’s movement


Lunar Eclipses

Earth’s shadow blocks the moon

Penumbral Lunar Eclipse

Partial Lunar Eclipse

Total Lunar Eclipse (full moon)

~⅓ of all lunar eclipses

~⅓ of all lunar eclipses

~⅓ of all lunar eclipses

Moon passes through Earth’s penumbral shadow, never

touches umbra

Moon touches/skirts Earth’s umbral shadow

Moon gets totally submerged in Earth’s umbra - moon appears red b/c atmosphere refracts the red light and the moon reflects it

Solar Eclipses

The moon’s shadow blocks the sun

Partial Solar Eclipse

Total Solar Eclipse

Annular Solar Eclipse

Some of sun’s light is blocked but not all

Sun’s light is completely blacked out, occurs when moon is at perigee - full moon

Earth, moon, & sun aligned perfectly but moon is at apogee and too far from Earth to

completely block sun - a ring of light is left around the moon - full moon

Corona is visible

Corona not visible

Corona - sun’s far atmosphere; only visible when all of the sun’s light is blocked

Solar vs. lunar eclipses

Lunar - everyone on night side of Earth can see, longer eclipse

Solar - very specific locations can see, moon’s orbit + Earth’s rotation = shorter eclipse - Same frequency as lunar eclipses but much smaller likelihood of seeing one

Eclipse seasons

~Every 6 months

- Not lunar eclipses every month b/c moon’s orbit around Earth does not perfectly line up with Earth’s orbit around the sun

- Not solar eclipses every month b/c moon’s orbit is inclined by 5 degrees to the ecliptic

2.2, 4.3-4.4

Ancient astronomy’s influence on modern calendar/clock


- One year = one orbit around the sun

- One month = one moon phase cycle (synodic month)

- One day = one rotation of Earth on its axis


- Noon = sun at meridian

- Obelisk - inspiration for modern clocks; 12 noon points straight up (north) and moves around clockwise (the direction the sun moves in the northern hemisphere)

- Egyptians broke day into 12 ante meridian (A.M. - before noon) pieces, and 12 post meridian (P.M. - after noon) pieces


- 7 days of the week for the 7 recognized planets


Estimated the circumference of Earth

● Realized the sun was at zenith on summer solstice above Sainis, Egypt but not Alexandria ● If sun is zenith in Sainis but 80 degrees altitude in Alexandria, it’s b/c you’ve moved 7 degrees around the sphere of earth

● 7 degrees = 1/50th of a circle, then 7 x 50 = circumference of planet

● Estimate - ~42,000 km; truth ~40,000 km

Using the circumference of Earth & latitude difference to determine actual distance ● Radius of earth ~ 6370 km

● Circumference of earth = 2πR (~40,003 km)

Equation for distance

● (distance between the cities in degrees)/(360°) = (distance between cities in km)/(circumference of earth)

● Ex: Polaris is 40° above the horizon in Fort Collins and 52° above the horizon in Saskatoon, how far apart are the two cities?

- 52 - 40 = 12° distance

- 12/360 = distance/40,003 (cross multiply and solve for distance)

- Distance = 1,333.43 km

Layout of solar system - according to ancient Greek astronomers

- Stars set in the sky

- Objects that seemed not only to rise and set, but to also wander around = planets - “Planet” = “wanderers”

- Planets named after roman gods

● Earth - wasn’t considered a planet bc it didn’t visibly wander across our sky

● Uranus - so far and moves so slow that they couldn’t tell it wandered

● Neptune - not visible to human eye so they didn’t recognize it as a planet

● Moon & sun classified as planets

Ptolemaic vs. Copernican Models

Ptolemaic Model

Copernican Model

Center of solar system



Orbital shape of celestial bodies

Perfect circles

Perfect circles

Why epicycles are necessary

Explain retrograde motion of planets

To make up for the incorrect assumption of circular orbits so that he could accurately predict planet positions

Greek explanation of retrograde motion

Retrograde motion - occasional slipping of planets WEST (backwards) over many nights ● Planet in retrograde - still rises in east and sets in west (always like this b/c earth rotates faster than the westward motion of the planets)

Reality of retrograde

Retrograde - planet doesn’t actually stop and move backward, we just lap the planet in orbit and it appears to move in reverse; truly it is still moving forward

- Imagine passing a car on the freeway; it’s moving forward but appears to move backward because you are moving faster

- Planets in retrograde do still rise in the east and set in the west

2.4, 3.1

Kepler’s Laws

1. Law of ellipses

Planets follow elliptical orbits ; sun at one focus in the ellipse

- semi-major axis: avg. of perihelion and aphelion distance in a planet’s orbit (radius of the orbit) 2. Law of Equal Areas

● The orbital speed of a planet varies in such a way that in a set amount of time, a line between the sun and the planet sweeps out over equal areas

- In a planet’s orbit, it moves faster when it’s closer to the sun and it moves slower the further from the sun that it moves

- Ex: In the figure, t is the time it takes a planet to move that distance in its orbit (both t are equal to each other). The areas of the two near-triangular shapes created by drawing lines from the sun to points on the orbit are equal (A1=A2).

3. Law of Harmonies

● P^2 = a^3

- P = Orbital period of a planet (in years)

- a = semi major axis of that orbit (AU)


Eccentricity - number between 0-1 that describes the flatness of an ellipse

● 0 = circular

● 1 = squished (parabola)

● Example on page 12 of copernican rev. Ppt

Galileo’s observations defeat the geocentric model

- There are moons that orbit Jupiter, so not everything orbits the earth

- Venus orbits the sun, so not everything orbits the earth (known b/c we see more than only New & crescent phases, which are all that we would be able to see if Venus orbited Earth) - Ancient astronomers thought no parallax = earth doesn’t move - but NO, no parallax = stars are very far away

- Ancient astronomers thought the heavens were perfect - NO, sun spots and lunar craters prove it is always changing


How we describe motion

Speed - rate at which an object moves

Speed = (change in distance)/time

Velocity - indicates both speed and direction

Acceleration - rate at which velocity changes (can be a change in speed OR direction! Or both) Acceleration = (change in velocity) / (change in time)

Acceleration of things falling with earth’s gravity — �� ≈10��/��2 or≈10��/�� ��

Force - push or pull that causes an object to accelerate

Newton’s laws of motion (3)

Law of Inertia 

- Objects move at constant velocity unless acted upon by an outside force

Law of Acceleration 

- Force = mass x acceleration (F=ma)

- Mass = amount of matter in an object

Law of Action/Reaction 

- For every force, there is always an equal and opposite reaction force

- Ex: rocket pushes gas out of nozzle, rocket is pushed forward

Law of gravity 

- Gravity is a mutual force

- MEaE = mpAp


- gravity follows an inverse square law; gravity’s force on an object is = 1/r if mass does not change

- F1 = F2 = G(m1xm2/r^2)

- F = force; m = mass; r = distance; G is a constant

How Newton described gravity (factors that affect the strength of gravity between two objects)

- Distance and mass

Why astronauts are weightless in space

Misconception - astronauts are weightless in space b/c there’s no gravity - false! - They are in a state of free fall constantly (just like all the planets), gravity keeps them in orbit

Major Contributions

Ptolemy - recorded the 48 ancient constellations from the northern hemisphere in the Almagest - Created the ptolemaic model with epicycles

Eratosthenes - figured out the estimate size of the circumference of Earth

Copernicus - credited for shift to heliocentric model

- Figured out how to calculate the distance of the planets

- Accurately described layout of the solar system

Brahe - proved that comets are not contained within the atmosphere

- Took detailed measurements of objects on the celestial sphere (most accurate measurements without a telescope)

Kepler - figured out that orbits are elliptical

- Proved heliocentrism was correct by using Tycho’s research

Galileo - provided concrete evidence that Kepler and Copernicus were correct about heliocentric model of the solar system

Newton - laws of motion and gravity

- Discovered that physics on Earth are the same as physics in space (gravity makes things go up & down on Earth but it makes things orbit in space)

- Invented calculus

- Discovered that sunlight is made up of all colors in the rainbow

- Discovered what affects the strength of gravity between two objects (mass and distance)


Metals - everything other than the first two elements on the periodic table (Hydrogen & Helium) Altitude - an object’s height above the observer’s horizon (zenith = 90°)

- Paired with azimuthal directions to create a coordinate

Azimuth - N,S,E,W directions; N = 0°, E = 90°, S = 180°, W = 270°

- Paired with altitude to create a coordinate

Equatorial coordinates- global latitude/longitude coordinates that are projected onto the celestial sphere Nadir - point directly below an observer

Zenith - point directly above an observer

Horizon - the line where the sky meets the earth (ground)

Meridian crossing - an object’s highest point in the sky

North & south celestial poles - points where Earth’s axis intersects the celestial sphere Celestial equator - halfway between celestial poles

Vernal equinox - point in the sky where the ecliptic crosses the celestial equator Constellations - sections of the sky used like maps

Asterisms - recognizable star patterns within constellations

Axial precession - gravity induced, slow shift in the orientation of Earth’s axis

Summer solstice - first day of summer; longest day of the year

Winter solstice - first day of winter; shortest day of the year

Equinoxes - first day of fall & spring; exactly 12 hours of daylight and 12 hours of darkness Anti noon - literally before noon (AM)

Post noon - literally after noon (PM)

Analemma - the sun’s position in the sky at the same time each day (moves each day) Helion - references an object’s position in its orbit of the sun (helion=sun)

Gee - references an object’s position in its orbit of the earth (gee=earth)

Perihelion - earth’s closest point to the sun in its orbit

Aphelion - earth’s farthest point from the sun in its orbit

Perigee - the moon’s closest point to Earth in its orbit (appears bigger in the sky) Apogee - the moon’s farthest point from Earth in its orbit (appears smaller in the sky) Geocentric - Earth centered view

Heliocentric - sun centered view

Sidereal - in relation to other celestial objects

Sidereal month - orbital period of the moon around the earth - 27.3 days

Synodic month - complete phase cycle of the moon - 29.5 days

Sidereal day - one rotation of Earth on its axis; 23 hours 56 minutes (one day compared to other celestial objects)

Solar day - one rotation of Earth so that the sun returns to its position at the beginning of the solar day; 24 hours (one day compared to the sun’s position)

- longer than a sidereal day b/c earth orbits the sun as it rotates and therefore needs a couple extra minutes to get the sun back into its original position

Tidally locked - the condition that means that we only ever see one side of the moon because the moon rotates at the exact speed that it orbits the earth (synchronous rotation - necessary for tidal locking) Umbra - the total shadow of an object; no sunlight reaches this area (umbral shadow) Penumbra - the partial shadow of an object; only some of the sunlight is blocked from this area (penumbral shadow)

Ecliptic - the apparent path that the sun takes across the sky

- Other planets and the moon are confined to it as well

Zodiac constellations - 12 constellations found near the ecliptic that the sun and moon pass through Circumpolar stars - stars that never fall below the horizon in a given area’s sky

Semi major axis - the radius of the longest portion of an object’s orbit, used to describe the size of an orbit

Recurring Questions/Notes 

- Polaris can be used for navigation - the altitude of polaris in a certain city represents the latitude of that city on the earth

- Ecliptic is at a 23.5 degree tilt from the celestial equator

- Moon does not glow, just reflects light

- One month = new moon to new moon

- Earth moon is pretty big comparatively to moons of other planets

- If Earth is a basketball, moon is a tennis ball

- They’re 24 feet away and Earth’s atmosphere is as thick as paper

- Annular solar eclipse happens when moon is at apogee

- Total solar eclipse happens when moon is at perigee

- Copernicus published a controversial book in 1543 that suggested the heliocentric solar system idea - A planet with a highly eccentric orbit will be much, much closer to the sun in some areas of its orbit than others

- Aristotle thought that the natural motion of something untouched on Earth is up/down and in space is circular b/c he thought that physics are different on Earth than in space

- If the Sun were replaced with a black hole of the same mass, Earth’s orbit would not be affected - Kepler’s third law (P^2 = a^3) means that

- The orbital period of a planet doesn’t depend on its mass

- A planet's period does not depend on the eccentricity of its orbit

- All orbits with the same semi-major axis have the same period

- Planets that are farther from the Sun move at slower average speeds than nearer planets - Orbital bodies are falling constantly

- Weight is not constant throughout the universe, mass is

- We can only see physically see Orion at night during the winter b/c in the summer, the sun is very near Orion and therefore Orion is only in our sky during the day, when the sun’s light blocks it out - Helpful slides to look at in the “moons” ppt. For visualizing why we see moon phases- Lunar phases overview slides

- The Argo Navis constellation was split up because it was too large to be a useful landmark - Diameter of the moon AND sun = .5°

- The milky way spans 100,000 light years

- Light travels 1 AU in 8 minutes

- 1° = 60’ (arcminutes); 1’ = 60” (arcseconds)

- Proxima Centauri is the closest star to the sun, about 4 light years from Earth

- The universe is roughly 14 billion years old; we can see ~14 billion light years of our universe - Ptolemy placed the sun between mars and venus in the Ptolemaic model

- The sun never goes into retrograde

- Review the cosmic calendar (calendar of the universe scaled down to one Earth year) - Solar system forms in September

- Humans appear 6 minutes before midnight on Dec. 31

Scale of the universe if the sun is grapefruit

Earth - grape

Moon - pea

Jupiter - grapefruit

*ON EXAM according to prof.*

1. if you’re living on the near side of the moon during this eclipse, what type of eclipse is it? Answer - partial solar eclipse b/c the moon is in Earth’s penumbral shadow, which blocks some but not all sunlight

2. If you’re living on the moon and the sun is on your meridian, it’ll take 29.5 days (synodic month) for the sun to be back on your meridian.

3. If a satellite orbits Earth at a constant speed, it IS accelerating (b/c it’s changing direction) 4. If a satellite orbits Earth at a constant speed, there IS a force acting on the satellite (gravity) 5. If Earth suddenly moved to an orbit around the sun of 3 AU, then the gravitational pull of the sun would become 9 times weaker (gravitational pull is inversely affected by distance; gravity = 1/r^2)

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