NATS 1740 Lecture Notes - Lecture 4: Refraction, Optics Algorithm, Dont
19 May 2018
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• NATS 1740
• TUES, MARCH 14
RECAP TEST 2
Focused on ASTRONOMY
→ Lecture 8 – Lecture 16
LECTURE 8:
• First lens was built in 1602 in Holland
• First telescope used for astronomy in 1608
• KNOW all the YEARS and telescopes and where used
• Know the technology used in telescopes
• #1The two lenses telescope
• Accuracy (magnification) LIGHT GRASP NOT MAGNIFICATION HE MADE MISTAKE is
related to the SIZE of the primary (first) lens
• Don’t need to know any PHYSICS optics
• Know the focal point
• #2Cassegrain telescope
o Advantages using MIRROR
▪ cost because it is hard to build a mirror so big with glass
o SOLUTION: replace glass with mirrors
▪ Build lens out of small lenses to make a big lens
o EXPENSIVE: to have one single lens that is metres in diameter
• Know that they need to be at high altitudes because of lights in city and in general are
NOT in cities and are outside the city
• Sky is richer in the SOUTHERN hemisphere and this is why you see EUROPEAN main
astronomical centre is in Chile
o Better in southern hemisoehre because you have DIRECT view of galaxy
o Density of stars is therefore double, if not more.
OPTICS:
• Reflection
• Refraction
• Why is the sweater black? What does it mean in terms of reflection and refraction
o The colour that you see is the colour REFLECTED assuming that the light coming
from the sun is a COMPOSITE of many colours
• How to break white light: with a PRISM and you can see this with a rainbow
o ROLE OF THE PRISM is played by the WATER molecules in an atmosphere
DON’T NEED TO KNOW:
• History of telescopes
find more resources at oneclass.com
find more resources at oneclass.com
SPECTRUM:
• Know ABOSPRTION SPECTRUM because it shows you what kind of atmos and molecules
are in the atmosphere in the source of light like a star
o Gives you composition of atmspehre of planet but it is complicated because
plaets do’t eit light, istead it eflet sulight the plaets atosphee
o So you have to eliminate what is in sun and then you get what is in planet
atmosphere
o Absorpitoin spectrum is BLACK LINES
DOPPLER EFFECT:
• You have the normal signature of an atom or molecule as SPECTRUM and you observe
that in the light coming from a star or galaxy
o This spectrum is still there but it is SHIFTED either towards RED or BLUE (two
ends of a spectrum)
o RED: source of light moves away from us
o BLUE: source of light moves toward us
• SPECTRAL ANALYSIS is useful in astronomy because the telescopes can be used to
collect the light and accumulate the light coming from a star
o To obtain that information, about planet, light is accumulate over time
o Sometimes light coming from far away is very weak and you have to accumulate
it
o This is why SPECTROSCOPY is very important because you apply it on
ACCUMULATED light
INTERFEROMETRES:
• Important for RADIO telescopes and ALSO for VISIBLE light
• Definition: at least two telescopes combining their images in a mathematical way to
obtain a SINGLE image of BETTER CLEARER RESOLUTION IMAGE
DON’T NEED TO KNOW:
• Henri Fizzou
NON-VISIBLE LIGHT:
• TO see universe only thorugh visible light is to see only a limited amount of things (like
white people in a room)
• Visible light is just a COMPONENT of electromagnetic spectrum
• All of electromagnetic spectrum move at speed of LIGHT.
• Differences related to in WHAT it moves: air, glass, water = different speeds in different
matter
DIAGRAMS:
find more resources at oneclass.com
find more resources at oneclass.com
• ONLY [visible light] and [radio] fully penetrate the atmosphere and get to sea level
• Others are stopped in atmosphere or PARTIALLY get to surface
• WHY can we only see visible light going to ocean level:
o Visible light and radio waves which we can hear and see because we adapted to
these forms of electromagnetic radiation
o Remember from extra-terrestrial life discussion → we adjust to conditions like
ats ho lie i aes use ultasouds eause the do’t see much with their
eyes
o We use visible light because we were adapted to whatever comes to the
GROUND level through elimination
o Visible light and radio waves were forever the two which came to the ground
level so from the very beginning these two were the wavelengths to reach
ground level
RADIO TELESCOPES:
• Unlike OPTICAL telescopes which use optics, RADIO TELESCOPES use electricity (radio
waves)
• Radio waves are related to electromagnetic ENERGY
• Radio programs produced by electrical wires
• Performance of adio telesopes: NOT IMPORTANT DON’T NEED TO KNOW
• IMPORTANT: interferometers are VERY important for radio signals because without
using interferometre, the radio telescopes are very BAD in RESOLUTION and you cannot
see details with a normal radio telescope
o Example: in new mexico, 27 tv type radio telescopes are providing ONE image
equivalent to something produced by kilometres of electric mesh
• Radio telescope is an ELECTRICAL MESH
• For anything that is not visible light or radio telescope → we observe that
electromagnetic radiation using DETECTORS not telescopes
• Telescope: what comes to ground level (or hubble telescope in space where images are
much better)
• Detector: observed on satellites, balloons, space stations
• What produces radio waves:
• What produces visible light:
• Hot objects like stars: PRODUCE visible light
• VERY hot objects like stars: produce infra red(heat), ultraviolet high energy, x-rays,
gamma rays
• Neutron stars: electrically charged particles moving in the cosmos at high speeds can
produce all kinds of electromagnetic radiation
o Speed low → produce radio waves
o Speed high → produce x-rays and gamma rays
o Neutron stars/PULSARS have material moving around it is at LOW speed so
produce radio waves
find more resources at oneclass.com
find more resources at oneclass.com
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NATS 1740 Full Course Notes
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Document Summary
Don"t need to know: history of telescopes. Important for radio telescopes and also for visible light: definition: at least two telescopes combining their images in a mathematical way to obtain a single image of better clearer resolution image. Ground level through elimination: visible light and radio waves were forever the two which came to the ground level so from the very beginning these two were the wavelengths to reach ground level. Radio telescopes: unlike optical telescopes which use optics, radio telescopes use electricity (radio waves, radio waves are related to electromagnetic energy, radio programs produced by electrical wires, performance of (cid:396)adio teles(cid:272)opes: not important don"t need to know. Gravitational waves: observed by ligo in 2015, definition: technology used by ligo is destructive interference of two laser beams which is so fine that as a result of the interference of these two beams, you get a very.
