astronomy ch 3&4 from slides

What are the units for 1 Newton?

1 N= 1 kg x 1 m/s^2

When was stellar parallax first measured?

1838

What happens if the object's speed exceeds the circular speed?

It will no longer be bound by gravity and will escape

What is perihelion?

The point in its orbit at which a planet is closest to the Sun

What were the three main objections to the Copernican heliocentric model?

1. Aristotle's belief that Earth was moving, objects on it would be left behind 2. Aristotle's belief that the heavens must be perfect and unchanging (noncircular orbits impossible) 3. No one had detected the stellar parallax that should occur if Earth orbited the Sun

What other two things did Galileo discover that disproved Earth-centered model?

1. Jupiter had moons that clearly orbited it, not Earth 2. Venus goes through phases in a way that meant it must orbit Sun, not Earth

What is aphelion?

The point in its orbit at which a planet is farthest from the sun

What is acceleration due to gravity on Earth?

9.8 m/s^2. It is always the same on Earth

What is Kepler's second law?

A planet moves faster in the part of its orbit nearer the Sun and slower when farther from the Sun, sweeping out equal areas in equal times.

What is Newton's first law?

An object at rest or moving at a constant speed in a straight line continues to do so unless acted upon by an external force. (aka Law of Inertia). Mass of a body is a measure of its inertia

What does gravity mean/do?

Any piece of matter attracts any other (even dark matter!). Gravity is always attractive

Who proposed the FIRST heliocentric model? Why didn't it gain support?

Aristarchus in 260 BC, but it never gained much support in ancient times bc of the lack of detectable stellar parallax

How can we explain Kepler's second law?

At perihelion, gravity is much stronger than at aphelion, so the planet moves faster when gravity is stronger and it is closer to the sun

Which move faster in our solar system, planets that are closer to the Sun or farther?

Closer

What keeps a planet rotating and orbiting the Sun?

Conservation of angular momentum

What is the formula for force of gravity between two objects?

Fg = (GM1M2)/d^2 **d is the distance between the centers of the two objects

What is Newton's third law?

For every action there is an equal and opposite reaction

What is Newton's second law?

Force = mass x acceleration (F=ma)

What is Kepler's third law?

More distant planets orbit the Sun at slower average speeds, obeying the relationship p^2 = a^3

How did Galileo disprove Aristotle's belief that the heavens were perfect and unchanging?

He saw sunspots on the Sun (considered imperfections at the time) and mountains and valleys on the Moon. Since the heavens were not perfect, then the idea of elliptical orbits as opposed to "perfect" circles was not so objectionable

How did Galileo disprove Aristotle's belief that if Earth moved, objects on it would not?

He showed that a moving object remains in motion unless a force acts to stop it (objects in motion stay in motion!)

What did Kepler do?

He was Tycho's apprentice, took over for Tycho after his death. Kepler found a set of circular orbits that were predicted planetary positions that were off by 8 arcminutes at the most from Tycho's observations. However, he knew that Tycho wouldn't have made these errors so he abandoned the idea. His key discovery was that planets orbited in ellipses, which allowed him to make the most accurate and accepted model of planetary motion

What was Copernicus's model like?

Heliocentric, he calculated each planet's orbital period and relative distance (compared to Earth's) from the Sun. He published a book but it didn't convert many people because his model didn't work very well. He used perfect circular orbits, so his system had to be very complex to make decent predictions and even then it wasn't more accurate than Ptolemaic model

Why did Aristotle believe that Earth could not be moving?

If it were, objects such as birds, falling stones, and clouds would be left behind as Earth moved along its way

What did Tycho Brahe do?

Made super accurate measurements of planetary motion, but he never came up with a satisfying explanation. He was convinced that we orbited the Sun but he thought the Earth was stationary because he couldn't detect stellar parallax. He created a model in which the Sun orbited Earth and all other planets orbited the Sun, but no one took this seriously.

How did Galileo explain the lack of detectable stellar parallax?

Provided strong evidence in favor of the stars being more distant than Tycho thought, and therefore too distant for him to have observed stellar parallax. Galileo found that the Milky Way resolved into countless individual stars= more numerous and distant than previously thought

What was the geocentric model that attempted to explain retrograde motion, and who made it?

Ptolemaic model made by Ptolemy; each planet moves on a small circle whose center moves around Earth on a larger circle. The small circle is called an epicycle, and the large circle is called a deferent. Ptolemy had to make the big circles slightly off-center from Earth so his model got really complicated. However, it was accurate enough to be used for the next 1500 years

The first model of planetary motion was created by ___________ and featured a ___________ Earth at the _______________ of a great celestial sphere.

The Greeks- geocentric model with a spherical Earth at the center of a great celestial sphere

What does conservation of angular momentum mean?

The angular momentum of an object cannot change unless an external twisting force (torque) is acting on it. Earth experiences no twisting force as it orbits the Sun, so its rotation and orbit will continue indefinitely (until some collision or another major event affects it)

What is the semimajor axis?

The average of a planet's perihelion and aphelion distances

What is Kepler's first law?

The orbit of each planet around the Sun is an ellipse with the Sun at one focus.

What's the difference between speed and velocity?

Velocity has direction

What is the formula for weight of an object on any planet or moon?

Weight = mg where g = (GM)/R^2

What is the formula for angular momentum?

angular momentum = mass x velocity x radius

What is speed?

rate of change of positoin

What is Occam's Razor?

the idea that scientists should prefer the simpler of two models that agree equally well with observations

What is the formula for circular speed?

v = (square root of) (GM/r) Can leave out the mass of the smaller object bc it is so much smaller that it is negligible. Must convert until M is in kg and r is in meters to get an answer in m/s, because G is in m^3/kgs^2