Astronomy 2022 September 19-21

Light can determine temperatures, speed/directions of motion, chemical composition, sizes, distances

Energy, a form of Electromagnetic Radiation

all forms of EMR travel at the speed of 186k miles/sec or 300k km/sec through a vacuum, cellphone travels at this speed

Produced as electrons transition from one energy level to another, if anything emits light electrons must be transitioning

Has wave like properties, practical like properties, you cannot draw a picture of something that is both a wave and particle but it’s true in theory

Can be described as ripples, light energy can be measured in wavelengths, measured in nanometers

Top of wavelength

Bottom of wavelength

Number of waves that pass a certain point in one second

Classifying EMR by wavelength, all types of EMR

Can be described as a stream of particles called photons, massless particle that carries energy at the speed of light

How long it takes for an image to travel, stars we see now are years old

Light can determine temperatures, speed/directions of motion, chemical composition, sizes, distances

.01 nm, most energetic EMR, produced in cores of stars during fusion reactions, dangerous

Light can determine temperatures, speed/directions of motion, chemical composition, sizes, distances

Light can determine temperatures, speed/directions of motion, chemical composition, sizes, distances

What we see, stars, lights, fire etc emit this, planets, clothes, colors reflect this, some nebula emit or reflect this. Purple at 400 red at 700

.1-300 nm, micrometer 10^-6, discovered by Herschel while taking temperature of different colors

1mm-1.0 meters, microwave oven, cosmic background radiation, microwave cell tower

1 meter-? kilometers, longest wavelengths, least energetic form of EMR

Earth’s atmosphere absorbs most forms of EMR from space, but if it makes it through, it passed through this

The study of light, determines chemical composition of stars, nebulae, atmospheres of planets/satellites etc

can be used by astronomers to determine the chemical compositions of stars

Four laws of spectroscopy

A hot solid, liquid, or dense gas produces a continuous spectrum (continuous color all the way across the spectrum)

A hot, low density gas produced an emission line spectrum (limited color)

A continuous spectrum source viewed through a cool, low density gas produces an absorption line spectrum

made of hydrogen, no other element has the same spectrum

Immediately the electron transitions from the higher energy level to a lower energy level, a single photon is emitted with exactly the energy difference between levels

an increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move toward (or away from) each other

Used by astronomers to measure the speed of objects moving towards or away from earth. Blue shifted=towards us, red=away from us

If the light source is moving towards the observer, the observed wavelength will get shorter and blue shifted. If it’s moving away, it will get longer and red shifted

measure of average kinetic energy of the particles in an object

higher temperature means greater kinetic energy

higher temperature means greatest vibrational energy

Measure of the total amount of kinetic energy in a system, different from temperature

used by astronomers, directly proportional to the internal energy, developed by William Thomson and Lord Kelvin

0k=absolute zero, -273 Celsius. 273 k is when water freezes

Determines surface temperature of a star, relates color (peak wavelenght) to temperature, determined using spectroscopy, temperature K = (2.9 x 10^6)/peak wavelength. hotter objects are blue, cooler red

Used to determine the total amount of energy released per second per unit area, relates energy to brightness in watts, renergy output is sensitive to temperature (t^4). Relates luminosity to total surface area/temperature to star