Astronomy Assessment 1

Cosmic Address Sequence

Earth → Solar System → Milky Way → Local Group → Virgo Supercluster → Laniakea →Universe

Earth’s Position

3rd planet from the sun. Earth takes 24 hours to rotate and 365 days to orbit the Sun.

Size of Earth

Size of the Solar System

Size of the Milky Way

Size of the Virgo Supercluster

About 8,000 miles.

About 2ly

About 100,000ly

About 110,000,000ly

Planets from the Sun

Sun→Mercury→Venus→Earth →Mars→Jupiter→Saturn →Uranus → Neptune →Pluto

Three Large Galaxies in the Local Group

1. The galaxy

2. The Andromeda Galaxy

3. The Triangulum Galaxy

Light Years

The measurement of light and the distance light travel in a year. how long it takes light to travel in a year. NOT based on time

Speed of Light

C= 300,000 km/s

1 AU

The average distance from the Earth to the Sun.

Speed

is how fast something can travel in sometime.

Velocity

speed or direction

Acceleration

change in speed and/or direction

Gravity

The invisible force that pulls objects down to earth or pulls any two objects with mass toward each other.

Earth’s Gravitational Acceleration

All objects accelerate at g=9.8 m/s² regardless of mass

Momentum

is a property any moving object with mass has. The equation is mass X velocity.

Momentum is essentially the inertia of a moving object, meaning it is the thing/property that makes a moving object want to stay in motion unless acted on by an external net force. Momentum is the reason your body leans out as your car goes around a curve, or momentum is the reason a truck smashing through a wall will continue to move forward even after breaking through the wall. It still has momentum, so it will keep moving forward. It is a type of energy, so it can be transferred via collisions. If the wall is thick enough, the truck can smash against it without breaking through, therefore losing all of its momentum to a different form of energy.

Net force

is the sum of all forces acting on an object. The sum of all forces acting on an object; a nonzero net force causes acceleration because there is either a change in speed or direction, or both.

Net Force would be Net Force = Force of friction + Force of air resistance + force that is making the object move in the first place. Now, force of friction and force of air resistance will pretty much always be opposite to the direction of motion, meaning that they will be negative, so they will be fighting against the force that’s moving the object. So you essentially subtract them from your net force. Here’s a diagram to hopefully help describe this (imagine just pushing or pulling on a block, and no other forces involved):

Torque

A special kind of force that changes angular momentum, depending on force magnitude (how much force is being applied) and the application point (toward the toque harder to push but further torque easier to push)

mass

Mass is the amount of matter in your body. The matter in a persons body.

Weight

Weight depends on mass and gravity.

International Space Station Free Fall

The international Space Station stays in space because it is still in Earth’s gravitation pull, it is constantly falling and missing Earth due to its high speed.

Newton’s First Law

An object moves at constant velocity (speed and direction) if there is no net force acting on it. An object will stay in motion unless a force acts upon it.

Newton’s 2nd law

Force=mass X acceleration (rate of change in momentum)

Newton’s 3rd Law

For any force, there is always an equal and opposite reaction force. Every object an an equal and opposite reaction force.

conservation of Angular Momentum

Angular momentum cannot change as long as no external torque is applied.

Kinetic Energy

The energy an object has due to motion, such as walking, falling, or meteors.

Potential Energy

Stored Energy held by an object because of relative position, electric charge, or internal stress. ex. battery

Mass-Energy Equivalence

E=mc²; a small amount of mass contains a massive amount of potential energy.

Universal Law of Gravitation

This is an equation that decribes how strong gravity is. t depends on the mass of the objects (Earth and Moon) and the distance between the centers of the objects. it also says that the strength of gravity falls off quickly as distance between the objects increases d²

Bound

objects will continue to orbit (Earth orbiting the Sun)

Circle shape and Ellipse more of oval shape

Unbound

object will pass by and will then fly ogg into space

Parabola and Hyperbola

Kepler’s Second Law

An imaginary line jpining a planet and a star sweeps out equal areas in equal amounts of time

Kepler’s 3rd law

p² = a³

p² = orbital period (how much time it takes for an object to complete one orbit around the word

a³ = is the “semi-majot axis” or radius

This is an equation that relates the orbital period to the average distance between orbiting objects.

Tidal Forces

differences in moon’s gravitational pull across Earth physically stretch it, creating two tides per day and two low tides.

Moon’s Synchronous Orbit

The moon rotate once per orbit around the Earth.

The Moon rotates once per orbit, meaning the same side of the Moon always faces Earth.

Thermal Energy

Kinetic energy of particles

• All particles always have some kinetic energy

• Related to temperature • Higher temperature (hotter) means particles are moving faster

• Temperature and Thermal Energy are not the same thing!

• Measured in Kelvin (K)

Colors of Light

White light contains all colors of visible light.

White= rainbow

White light is made up of all the colors of visible light.

How do we Expereince light?

• Warmth =energy

• Emission (glow in the dark)

• Absorption (absorb all the other colors)

• Transmission (transparent objects transmit light)

  • translucent -only some light (water bottle)

  • opaque objects block (absorb light (black out curtain)

• Reflection/Scattering

Why does an object have color?

The appearance of objects depends on how light interacts with matter. A red rose is red because it reflects red light and absorbs all the other colors of light. INTERACTIONS BETWEEN LIGHT AND MATTER DETERMINE THE APPEARANCE OF EVERYTHING AROUND US!

What is light?

light has a wave-particle duality, meaning it is both a wavelength and a particle. The particle of light is called a photon.

Waves

A wave is a pattern of motion that carries energy without carrying matter.

Wavlength

the distance between two corresponding points on a wave. measured from peak to peak or trough to trough

Frequency

Number of times per second that a wave vibrates

If light is both a particle and a wave then what kind of wave is it?

Light is an electromagnetic wave.

Electromagnetic waves consist of:

• An electric field

• A magnetic field

the electro and magnetic feild travel together and are 90 degrees apart from each other

Photons

A photon is a particle of light. Think of a photon as a packet of energy.

Important facts:

• Photons are particles of light.

• They are packets of energy.

• A photon has a wavelength and frequency.

• Photon energy depends on its frequency.

short wavelength = higher frequency = higher energy

longer wavelength = lower frequency = lower energy

The Electromagnetic Spectrum

From longest wavelength / low frequency/ lowest energy to shortest wavelength / high frequency/ highest energy:

Radio → Microwave → Infrared → Visible → Ultraviolet → X-ray → Gamma ray

Polarization

Polarization describes the direction of vibration of light.

• Linear polarization

• Circular polarization

• Elliptical polarization

reflection can change polarization.

Polarized sunglasses

Polarized sunglasses block light except for a particular polarization.

Infrared Light

Infrared (IR) is electromagnetic radiation beyond visible red light. This light has a longer wavelength = lower frequency = lower energy.

It is strongly associated with thermal radiation/heat:

The lecture asks you about:

• How objects look in infrared

• How hot and cold objects appear

• What animals look like in IR

• Which objects are transparent (black bagO/opaque (glass) to IR

• Why astronomers care about what IR light can pass through.

Important to astronomy idea: Different wavelengths allow astronomers to see different things. Something that blocks visible light may allow some infrared light to pass through.

Structure of Matter

An atom contains:

Nucleus

contains:

• Protons (+)

• Neutrons

Almost all of the atom's mass is in the nucleus.

Electron cloud contains:

• Electrons (-)

The majority of an atom's volume is essentially empty space.

Atomic Number

Atomic number = the number of protons in the nucleus

This is one of the most important definitions.

Atomic mass number

Atomic mass number = protons + neutrons

Neutral Atoms

Same number of protons and electrons.

Example:

10 protons + 10 electrons = neutral.

Molecules

A molecule contains two or more atoms.

Example:

He = helium atom

h2= dihydrogen = molecular hydrogen

02= dioxygen = molecular oxygen

Ions

An ion has the same number of protons but a different number of electrons. This happens when an atom gains or losses electrons.

Isotopes

Isotopes have:

same number of protons

different number of neutrons

because they have the same number of protons, they are the same element.

Changes of Matter

1. Ionization

stripping electrons from atoms. this can change atoms into plasma.

2. Dissociation

Breaking molecules into individual atoms.

3. Evaporation

This lecture describes this in terms of breaking flexible chemical bonds.

4. Melting

This lecture describes this as breaking rigid chemical bonds and changing a solid into a liquid

Energy Levels in Atoms

This VERY important for spectra.

Electrons in atoms are restricted to certain energy levels. They cannot have just any energy. Energy changes happen by moving: from one energy level to another

rather than moving continuously between levels

Electron Moving DOWN = EMISSION (glowing gas)

When an electron moves from a higher energy level to a lower energy level:

It releases energy.

This energy is released as a photon.

Therefore:

Downward transition → photon emitted → emission line

Electrons MOVING UP = ABSORPTION

When an electron moved from: lower energy level to higher energy level it must absorb energy.

Therefore:

Upward transition → photon absorbed → absorption line

Three Basic Types of Spectra

1. Continuous Spectrum

A continuous Spectrum contains all wavelengths without interruption. The spectrum of a common (incandescent) lightbulb spans all wavelengths, without interruption

Example:

A common incandescent lightbulb produces a continuous spectrum.

🌈 continuous rainbow

2. Emission Line Spectrum

A thin/low (HOT) density cloud of gas emits light at specific wavelengths. this produces: Bright lines

3. Absorption Line Spectrum

A cloud of gas between us and a lightbulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum.

Chemical Fingerprints

Every atom has q unique set of energy transitions.

Each transition corresponds to a specific:

• Energy

• Wavelength

• Frequency

gives each element a unique spectral pattern, like a fingerprint.

Downward transitions emit photons, so produce emission lines

Upward transitions absorb photons. so produce absorption lines

Why is this important?

By observing the spectrum of an astronomical object, astronomers can determine what chemicals/elements are present.

Molecules have more energy Levels

Molecules are more complicated than individual atoms.

Molecules can:

rotate

vibrate

Therefore, molecules have many additional energy levels. There are a large number of rotational and vibrational energy levels

This makes molecular spectra very complex.

Many molecular transitions occur in the infrared.

Thermal Radiation 2 Laws

1. All objects emit thermal radiation

2. This spectrum depends only on an objects temperature. Extremely hot = red/white and cooler = purple

3. Hotter objects emit more light at all frequencies per unit area.

4. Hotter objects emit photons with a higher average energy.

5. Hotter = more radiation + higher-energy photons

Doppler Shift

Doppler Shift allows astronomers to determine the motion of distant objects because of the wave nature of light.

Moving toward you

wavelength becomes:

shorter

light appears:

blue shifted

Toward us = blue shifted

Moving away from you

wavelength becomes:

longer

light appears:

redshifted

Easy memory trick:

BLUE = coming toward YOU

RED = moving AWAY

Measuring Doppler Shift

Astronomers generally measure Doppler shifts using spectral lines.

The amount of the shift → tells us the speed of the object

The direction of the shift → tells us the direction of motion

Measuring the shift:

Tells us only about the part of the object's motion that is toward ot away from us. It does not tell us the object’s complete motion.

Rotating Objects

Different parts of a rotating object move toward or way from us.

This causes Doppler shifts on different sides.

Slower object rotates = thinner lines. A spectral line from Star A is narrow because light from different parts is shifted only slightly from the center.

Faster objects rotates = wider lines. A spectral line from Star B is broad because light from different parts is shifted further from the center.

double-slit experiment

The double-slit experiment is one of the best demonstrations of wave-particle duality, which connects directly to your lecture's statement that light can act as both a wave and a particle.

Basic Setup

You have:

Light source → two narrow slits → screen

Light passes through the two slits.

If light behaves like a wave, the waves from the two slits interact with each other.

This creates interference.

Constructive Interference

When waves meet in phase, they reinforce each other.

Result: ➡ Bright band

Destructive Interference

When waves meet out of phase, they cancel each other.

Result: ➡ Dark band

So instead of seeing just two bright spots behind the two slits, you get a pattern of:

Bright → Dark → Bright → Dark → Bright

This is called an interference pattern

Special Relativity

Relativity involving high-speed motion

General Relativity

Relativity involving gravity

Special Relativity: First Postulate of Special Relativity

The laws of nature are the same for everybody.

Special Relativity: Second Postulate of Special Relativity

The speed of light is the space for everybody

Special Relativity: Time dilation

the phenomenon where time appears to pass more slowly in a moving object.

ex. space shift moving really fast only 25yrs old. twin stayed on earth and is 30 yrs old

Special Relativity: Length contraction

Fast-moving objects appear shorter in the firection of motion

Special Relativity: Mass increase

A force applied to a rapidly moving object produces less acceleration due to an effective mass increase. Rapid motion makes acceleration harder.

Spacetime

A 4D combination linking space and time together. Special relativity showed that space and time are not absolute meaning they are different based on who is observing

General Relativity: The equivalence Principle

The principle stating that the effects of acceleration are exactly equivalent to those of gravity.

General Relativity: Weightless in free-fall

Someone who feels weightless may be in free-fall

General Relativity: feels force

Someone who feels a force may be hovering in a gravitational field

General Relativity: Gravity

Result of curved space time. mass of sun makes everything curved

Rubber Sheet Analogy for Gravity

Mass curves spacetime. Heavier mass cause a even greater dip in the sheet.

Event Horizon

The point in no return near a black hole where spacetime is so curved that nothing can escape.

Gravitational Time Dilation

higher altitudes = weaker gravitational field = time moves faster

low altitudes = stronger gravitational field = time moves slower

Gravitational Lensing

The bending of light by curved spacetime, causing apparent positions of background objects to shift.

Einstein ring

Ring of light produced by gravitational lensing or when the gravity of a foreground galaxy bends light fron an object directly behind it.

Gravitational Waves

Ripples in spacetime produced by yhe movement of massive objects