Exam 2 part 1- telescope and detectors

the job of a telescope

collect light and angle it towards a focus point

focus place of a telescope

where the light angles to so we can see it

if you double the diameter of a telescope, how much more light will you be able to collect

4 times as much light

two types that telescope bring light to a focus

refraction, reflection

refractors

refraction refers to the change in direction of light when it goes from one medium to another, specifically shaped to bend light

parallel light rays of a refraction telescope

hit different parts of the lens converge to a point at a focal plane

eyes resemble which telescope light

refraction

reflectors

telescope with mirrors, most modern

why did refractors go out of date

glass is heavy and hard to support it need to be perfect, causes blurring

blurring of refraction telescopes

lenses focus light of different wavelengths at slightly different distances from the lens

the largest refractors telescope in the world

Yerkes telescope in Willliams Bay Wisconsin

polished glass of a reflector telescope is coated with

silver or aluminum

4 important ways telescopes aid our eyes

light gathering power, resolving power, magnification, sensitivity

light gathering power of a telescope

the number of photons collected per unit time. Bigger telescopes collect more photons which improves our ability to see faint objects

resolving power of a telescope

the ability to reveal fine detail. Bigger telescopes have higher resolution

magnification of a telescope

the ability to make images bigger. This is the least important property of modern telescopes. A highly magnified blurry image isnt of much use

sensitivity of a telescope

the ability to collect light at wavelengths that the human eye cant see

does size of a telescope matter

yes; larger apertures allow more photons to be collected per unit time, making it more efficient to take pictures of dim objects

telescope aperture

diameter of the main optical element

light gather powering of a telescope

collecting area= (pi)D^2/4

whats the largest telescope in the world

The FAST Radio telescope- Guizhou China

Radio telescopes

reflectors to collect & focus radio waves; radio waves have long wavelengths so big reflectors are needed to achieve even modest angular resolution

what is the mirror part of the radio telescope what does it do

concave dish, collects long wavelengths for angular resolution

what determines telescope resolution

diffraction pattern- when initally parallel waves pass through a small opening the wave crests bend and create a diffraction pattern

diffraction

causes the light coming from an individual point to be spread out more- this is our ability to discern fine detail

how to characterize resolution of a telescope

by measuring the smallest angular separation that two points of light can have and still appear well separated

factor limiting our resolution

Earth atmosphere

-light traveling through pockets of warm and cool air bends a little causing the image to smear

why do stars 'twinkle'

as the pockets of air move, when the atmosphere is stable there is less twinkling and we say the SEEING is good

diffraction limit

((2.5 x 10^5) arcsec x (wavelength/D))

how can we achieve high angular resolution in radio

combining separate telescopes to the equivalent of one giant telescope

photographic plates

-original images of the sky: placed their eye at the telescope focus

-sensitive to 1-2% of incoming photons, just like the eye

Electronic Light Detectors: Charge Coupled Device (CCD)

-typically capture 95-98% of incoming photons (100x more sensitive than photographic plates)

how does a CCD work

-layers of semiconducting material divided into lots of square regions of PIXELS

-incoming photons cause electrons to become unbound from their atom

the _____ of each pixel in the image corresponds to the number of ______detected in a CCD

brightness, photons

where are CCDs in real life

phone cameras, digital video cameras

CCDs dont what

detect color

color in digital images

CCDs tell us the number of photons detected but not their wavelength

how do we make color images

filters

transmit light only over a certain narrow range in wavelength (red, green, and blue filters)

false color images

can take images at wavelengths not visible to the human eye and assign them colors, to see features we otherwise miss

why launch telescopes into space?

-Earths atmosphere absorbs many wavelengths of light

what does not reach us through Earths atmosphere

y rays, X rays, some UV

JWST

James weeb telescope

several hectogonal mirrors

REFELCTING

INFRARED

Hubble is _______ than JWST, but has a better _________ because Hubble obersves shorter wavelength light

smaller, angular resolution

JWST has a_____ to keep it cool

sunsheild

What can we learn with JWST

star formation, exoplanets, star evolution, galaxies, early Universe

the ecliptic

the apparent path the sun takes in the sky

if we watch the path of the planets over the course of months, we see them move relative to the background stars

wandering stars

retrograde motion

star's direction of motion changes

the heliocentric model of motion

the OG model

used perfectly circular orbits for all planets

WRONG

Kelpers law 1

the orbits of the planets are ellipses with the Sun at one focus

Kelpers law 2

an individual planet moves fastest when closest to the Sun, and slowest when farthest away. The planet sweeps out an equal area of the ellipse in an equal interval of time

Keplers law 3

distant planets take longer to orbit the Sun than planets closer in. The orbital period (P) and their semimajor axis (A)

Kepler law 3 formula

(Pyears)^2 =(a)^3

Keplers third law of motion helps explain

retrograde motion, Earth orbits the Sun faster than planets orbiting at larger distances

velocity factored in Keplers formula

v^2 = (2pi)^2 / a

Earth moves faster than Mars

when it cached up and passes Mars briefly we see

it appears to move backwards relative to the background stars- retrograde motion

Keplers laws do not explina

what causes these acts of motion

Isaac Newton was the first to

explain WHY the Earth moves around the Sun, and not vice versa

Newtons 1st law: Inertia

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Newtons 2nd law

Force = mass x acceleration

more mass, needs more force for equal acceleration

Newtons 3rd law

whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first body

speed

how fast an object is moving

velocity

how fast an object is moving and in what direction

acceleration

a change in velocity or direction

momentum

momentum = mass x velocity

Newtons laws of motion are the consequence of

fundamental conservation laws

1 conservation of momentum

the total momentum of interacting objects cannot change unless an external force is acting

2nd conservation law

conservation of angular momentum

-any object that is spinning or moving along a curved path has angular momentum

the total angular momentum of the system cannot change unless

an external torque is acting

any objects angular momentum can only be changed if a twisting force or ______ is applied

torque: twisting

provides a physical explanation for Keplers 2nd law

conservation of angular momentum

explains why stars that forming are disks embedded in gas

conservation of angular motion

3rd conservation law

conservation of energy

-energy cannot appear or disappear it can only be exchanged among objects

3 basic types of energy

kinetic: motion

potential: stored

radiative: light

thermal energy

a type of KINETIC

particles moving randomly in substance, higher particle movement = higher temperature

Newtons universal law of gravity

every mass exerts a force of attraction on every other mass. The strength of the force is directly proportional to the product of the masses divided by the square of the distance between them

Newton's formula of gravity

LARGER MASSES HAVE A GREATER PULL

F1=F2 =G x m1xm2/r^2