Astronomy 101-2st Midterm

zenith vs nadir

-zenith is the point in the celestial sphere directly above the person- top of dome directly overhead

-Nadir is the point directly below

what is the astronomical unit? AU

distance from center of earth to center of sun-1.496×10^{8 km}

used to measure long distances in the galaxy

What does it mean to be a polymath?

To have a wide range of knowledge skills, or different jobs

What is polaris?

The north star, which is located close to the direction of the celestial north pole so can help with directions by letting us know which direction is north

-because it never sets 

What is a light-year?

the distance light travels in one year, 9.46 × 10¹² km

is used to measure the distance of things extremely far away because light travels very quickly

what is the geocentreic model?

-A model that represents the universe as earth in the center with all celestial bodies circling it

-almost everyone /ancient people before the renaissance used the celestial sphere to show how everything was just a circle around the earth which made sense to them and was evidence to prove what they were seeing

-was preserved more by the church who was able to remain powerful if there were more people that believed in god/ that god had picked them as the center of the universe, rather than not being in the center.

what is the heliocentric model?

the model that represents the sun being in the centre with us and other planets circling it

-was proposed by Aristarchus, but wasnt fully accepted until 1700s

how are the seasons created?

because the earth does not rotate perfectly vertcle on its axis, but on an angle

23.5 degree angle

-depending on its position around the sun, that angle may be facing away, towards,or adjacent to the sun, which creates the longer days

the difference in heat is caused when the sun is further away or closer to the earth/ at a different angle; and the more sun rays in a smaller angle the more intence that light is, so its more intence in the summer when closer and less so in the winter

what is the celestial sphere?

the idea of a giant circle surrounding earth that rotates around us every night and day; confirms the geocentric idea

-thought that it turns on the axis, instead its earth turning

-can still be helpful idea to mark out the location of things in the sky, just not correct

Aristarchus (of samos)

310-230 BCE

-created one of the first known models where the earth went around the sun (heliocentric model)

-Was rejected; heliocentric model wasn’t accepted until the 17-1800s

Isaac Newton

1643-1727 CE

-Figured out how to explain things in the physical world no one had thought about before

-created three laws of motion that determine how everything in the universe moves, including everything off of the earth

explain newton first law

-law of inertia

Every object will continue to be in a state of rest or move at a constant speed in a straight line unless it is compelled to change by an outside force.

explain newton second law

-When you apply a (net) force, an object will accelerate!(how quickly a object changes speed or direction) meaning an object will change speed and/or direction

-The change of motion of a body is proportional to and in the direction of the force acting on it

explain newton third law

every single force is created by something, and you need something to push and something to be pushed.

when they interact/ push against each other both things will feel the same amount of force (equal and opposite)

it just depends on the sizes; as although a smaller/ lighter thing will feel the same amount of force as a larger thing, it will be affected more than the larger thing

-like if i push the person next to me by their chest, they might move from the force- i feel the exact same amount of force against my hands when i push.- because a wall is stronger/ more sturdy than a person, when i push it again we both feel the exact amount of force, but because the wall is strong it doesn’t move; and the amount of force i use to try to move the wall might hurt my hand-

affects non-physical force too

when calculating the pull of two objects gravity forces, use grav. constant (6.67×10^-11) the mass of the two objects (kg) and the distance between them (meters)

explain aristotle

384-322BCE-first on list

knew that moon was closer than the sun because of solar eclipses where moon passes in front and blocks all the light

-Believed the earth was round because the shape of the shadow on the moon after solar eclipse was round, and if it were flat then it would show as a straight line sometimes

-also because the stars change wherever you travel, and if the earth was flat you would see the same stars all the time

eratosthenese

276-194 BCE

-Figured out earth’s size/ circumference and proved is not flat because of his study of the two cities

because sun was at different angles at the same time of the day for each place, he found the angle they made and used it in comparison to 360 degree measurment

hipparcus

190-120 BCE

-Discovered that location of north star had changed overtime; direction of rotation of sky changes slowly but continuously. (precession-earth rotating and moving: like a top)

-Collected list of around 850 examples of stars and their locations in the sky, and categorised by their brightness(apparent magnitudes)

Ptolemy

100-170 CE

-Created a geometric (earth in the middle) representation of the solar system that predicted positions of planets at any date and time;  left data for the intention of future generations to build off

-Created book with massive amount of astronomical knowledge-Almagest (the greatest); how have have gained the knowledge of greek astronomers, especially hipparchus

scientific notation/ exponents

-Makes really big and small numbers easier to understand

-move the decimal place of the number to the front, and use “ten to the power of”; represents how many numbers aren’t being shown- 

10⁴ =10×10×10×10

List the names and order of the astronomers for this setion

Aristotle-384-322 BCE

Aristarchus-310-230 BCE

Eratosthenes -276-194 BCE

Hipparchus- 190-120 BCE

year zero

Ptolemy- 100-170

Copernicus:1473-1543

Tycho Brahe:1546-1601

Galileo:1564-1642

Kepler:1571-1630

Newton- 1643- 1727

Nancy Grace Roman:1925-2018

what is the synodic day

24 hours-

earth rotation relevant to the sun, because since its also orbiting sun it has to turn a bit extra each day to have the sun at the same angle- has to go 361 degrees

what is the sidereal day

23 hour, 56 minute, 4 seconds

earth rotation relevant to distant stars

-they are so far away that its just the actual full time it takes for the full 360 degree rotation

what makes it hotter in the summer

In the summertime the earth is angled towards the sun differently so that the ground has more rays concentrated in a specific spot. The more intense rays causes the rise in temperature. when compared to the same amount of light being spread over a greater distance in the wintertime its colder

what is a comets tail made of? what directon does it alwasy point?

-Is made from particales of dust/ ice

-unlike popular belief, tail isnt showing the direction of comet, as tail always points away from the sun. the tail is just stuff being blown off the comet by the force from the sun

difference between a comet and a meteor

meteor- small, space dust burning up in our atmosphere

comet-Bigger icy object orbiting the sun; the tail always points away from the sun as it travels

difference between precision and accuracy

Accurate means something is correct-

Precise is how specific you are with something-

-i am between 3 and 6 feet tall: accurate because correct, but very wide range/ vague so not precise

-i am 5’9”.3678364: precis because very specific number, but not accurate because i am not 5’9”

-precise and accurate= i am 5’3”.4563

list the planets in order from the sun

mercury,

venus,

earth,

mars,

Jupiter,

saturn,

uranus

neptune

what is net force?

when the sum of all forces acting on an object are more than zero.

we all have gravitational force, and other force like the ground on us or when sitting in a chair affect us at all times; and these forces dont equal more than zero so thats why we can stay seated without falling or moving around (the chair pushes back on us to keep us sitting still)

but if another force is applied that causes the sum of all those forces on us to be less than zero, we move. like a push on the shoulder causes the value of your net force to become more than zero. we experience the opposite force back, and maybe move in the direction the push came from. Cause us to accelerate (even if just a little)

vector indicates which force is stronger than the others and determines what direction we will be pushed in/ move

what is vector?

a quantity that has both magnitude (size) and direction- something that is going some way-

-Velocity is a type of vector

shown as the arrow that represents the amount of force (based on length) and directing, based on the direction the arrow is pointing

what is the difference between speed and velocity?

-speed is how fast something is going

-velocity is how fast and in what direction/ has vector

define acceleration-

how quickly you change speed and/or direction; from slowing down or speeding up

sun sets in the- and rises in the-

sets in the west

rises in the east

What is a newton?

a unit of force-

the force required to accelerate a mass- one kilogram by one meter per second squared

definition of mass,

Mass-how much matter makes up an object; how much it contains

what is the (newtons) universal gravitational constant? (number and explanation)

6.67×10^-11 —— unit is N²/Kg²

^{newtons squared by kg squared}

symbol is capital G!

Quantifies the strength of gravity in our universe/ lets us turn the force into a measurable number

differcnce between mass and weight?

Weigh is the force of gravity by something on an object. that’s why you weigh less on the moon. the moon is a smaller mass and therefore has a smaller gravity, so its gravitational force pulls less on you, in comparison to how much the earth pulls on you, making you weigh less

mass is the amount of matter an object contains. like you there were 7×10²⁷ atoms, always make up about that may atoms no matter which planet you’re on. however those atoms do weigh less on the moon because of the moons lighter gravity force

definition of density

Density- how tightly material that makes up an object is packed (a brick is more dense than cotton candy)

definition of volume

volume- how much space an object takes up (car has more volume than a balloon)

What are the two main systems for locating celestial objects?

Horizonal-local

Equatorial- global

Explain horizonal location system

-changes depending on where you are; can only be used locally

Explain equatorial location system

what equation do you use to calculate the force of gravity

where on the globe would you see this kind of moon phase? why?

where on the globe would you see this kind of moon phase? why?

where on the globe would you see this kind of moon phase? why?

where on the globe would you see this kind of moon phase? why?

what did we learn in class about place value? explain

look at the units and spot of number; number is irrelevant unless you know units

What is keplers first law?

-planets orbit in ellipses, not circles

-the big object causing the planet to orbit (sun) is at one focus point of two spots within the center of the ellipse

what is keplers second law?

-as planets are moving around the sun, they sweep out equal distances at equal times.

-when far away= move slowly, the slice of pie is really narrow but long

-when close by= move really fast, the slice of pie is short and thick

If both examples took the same amount of time to travel, it means their distance/ area is the same

what is keplers third law?

-The period and radii(radius orbit) of a planet are related by the equation T²=a³

-related in earth years

-Time squared equals the semi major axis cubed

-keplers law changed by newton/ his addition

what is an ellipse/ how does it work?

-Planet usually dont orbit in perfect circles, but ellipses. the force of gravity from other objects on something orbiting pulls it in a different direction from the thing being orbited

-there are the two foci (singlular focus) within the ellipse, with the orbitee at one of the two points. 

-If an ellipse is circular enough, the foci are both in the center and become one point

what is momentum?

-A quantity that describes an objects tenancy to keep going or slow down.

-Depends on velocity/ speed, and mass

-The bigger and faster an object the harder it is to stop/ the more momentum it has

what does conservation of angular momentum mean? explain

whatever momentum you have, you have to keep

-have to loose something to gain something

-like the ice skater: when their arms are stretched out while spinning they go slower, but when they tuck their arms in they actually loose mass! have less surface area which makes less air friction, and gain more speed

what is the difference between momentum and angular momentum?

Momentum- an objects linear motion

Angular momentum- an objects rotational motion

What is meant with the equation T²=a³?

the equation for kepler’s third law

-is used to find the period of revolution around the sun for planets, in earth years. the amount of time it takes to do one full orbit

T=time in earth years

a= means axis, or semi major axis/ the distance from the center of the ellipse to the widest part of the ellipse- measured in astronomical units

-If we have either of these pieces of info it can help us find the other

What are the two main types of energy?

Potential

Kinetic

what are the three things that determine how much potential energy something has?

-Gravity field- more gravity=falls faster

-Its mass

-How far it will fall; how far from the ground it is

-Like if you held a baseball that weighs 150 grams 10 feet above the ground on earth- 

=has a lot less potential energy than if you held a bowling ball 20 feet above the ground on bigger planet with a stronger force of gravity

what is the conservation of momentum?

-the total momentum of an isolated system remains constant

-similar to conservation of angular momentum, but angular momentum is special because its just for spinning objects

what is meant by eccentricity?

-helps describe the shape of an elliptical

-depending on how close it is to a circle

-circular elliptical is value of 0, while more extreme or oblong elliptical is closer to 1.0 (like a 0.7, or 0.9)

how do you find the eccentricity value, or ε?

use equation-

ε=foci separation, divided by the major axis (on equation sheet)

foci separation- how far apart the two main points of the ellipse are; the farther apart the more oblong

major axis- the length of the ellipse hot dog style/ long way; the longer the more oblong

what is uniform circular motion?

-Movement of an object along a circular path

speed of object doesn’t change but direction constantly does=change in acceleration

what does the equation 𝐹𝑛𝑒𝑡=𝑚𝑎 mean?

Newtons 2nd law; when you apply a net force an object will accelerate

-Used to find an object’s net force when you have its mass or acceleration, or the other way around

What do you use the equation 𝑣=√𝐺𝑀/𝑟 for?

-to calculate the orbital speed of an object in a stable circular orbit around a larger mass! 

-using the gravitational constant, the mass of the thing being orbited, and the orbital radius (usual distance of altitude and radius of big mass), can find how fast moon is moving around

How do you find the orbital radius? or r

use the altitude provided and then add the radius of earth

make sure they are in the same units! m or km?

how do you find the orbital period of something?

use T²=a³

how do you find the semi major axis of something?

use T²=a³

-Orbital periods of planets are listed on the sheet