Chapter 4: Light ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4 - - PowerPoint PPT Presentation

Fall 2019: Chapter 4 ASTR/PHYS 1060: The Universe

Chapter 4: Light

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Light is a wave

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Tacoma Narrows Bridge, 1940

https://www.youtube.com/watch?v=XggxeuFDaDU

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Light is an “electromagnetic wave”

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Speed of Light: can you explain how we can measure it via this method?

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

A light-year is a unit of…

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A) Energy B) Time C) Distance D) Time and Distance

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

A light-year is like a parsec, but 3.26 times shorter

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Fall 2019: Chapter 4 ASTR/PHYS 1060: The Universe

Chapter 4: Light

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• Ch. 5 Reading Quiz due this Thursday

If you will miss class, email astr1060absence@gmail.com BEFORE the start of that class Midterm 1 Exam on Sept. 19th (1 week from Thursday)

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Light is “quantized” Its energy is proportional to frequency

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Electromagnetic Spectrum

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

What type of emission do we see only from the most energetic events?

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A) Visible Light B) Radio Waves C) Ultraviolet Light D) Gamma Rays

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

What is a spectrum?

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Wavelength [nm] Intensity/Brightness

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Which object would look bluer? Which object would look brighter?

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Wavelength [nm] A B Intensity/Brightness

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Emission and Absorption Lines

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Emission sticks up Absorption sticks down

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Our eyes are telescopes!

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Works like a refractor amount of refraction depends on the wavelength of light — cannot focus red and blue light at the same time!

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Astronomical Sources are “infinitely” far away

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Use reflecting telescopes due to less chromatic aberration and easier to build large ones

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xkcd.com

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Why do astronomers keep making telescopes

bigger?

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A) Increase the field of view of a single

• bservation

B) Resolve finer details (better image resolution) C) Collect more light D) Astronomers need to compensate for something

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Telescope Resolution

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

What is “angular resolution”?

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A) The angular size of a pixel of a CCD or any detector B) The smallest resolving power of a telescope’s mirrors C) The angles light must be bent by mirrors D) A solution to a tricky problem in optical design

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Making Images

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Charged Coupled Devices (CCDs)

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Filters

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“True” Color “False” Color

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False color images can be made using light at any wavelength, from radio to gamma ray “True” Color

Fall 2019: Chapter 4 ASTR/PHYS 1060: The Universe

If you were designing a telescope to survey the entire sky to study the brightest stars in several colors over the course of a year, what features would you want it to have?

large/small FOV? large/small mirrors (collecting area)? 1 big telescope vs. several smaller telescopes? a refracting or reflecting design? Discuss in small groups!

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Brief Tour of the Universe at Different Wavelengths

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low energy high energy

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Radio (broad band)

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Jupiter Captured charged particles from the Sun Centaurus A Galaxy Jets accelerated by a supermassive black hole

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Radio (narrow band)

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Hydrogen gas through emission line at 21 cm Visible light (stars - images at the same scale) Spiral Galaxy

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Infrared - Dust Clouds

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Visible Light Infrared Light (1-2 μm)

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Ultraviolet - Massive Stars

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M81

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

X-ray - Dead Stars

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X-ray (Chandra) Infrared (Hubble)

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The Crab Nebula

(Remains of a supernova, with a pulsar at the middle)

Crab Nebula supernova explosion left a pulsar at the center that energizes surrounding gas

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Radio/X-ray - Million Degree Gas in Galaxy Clusters

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Red = Radio Yellow = Visible Blue = X-ray

ASTR/PHYS 1060: The Universe Fall 2019: Chapter 4

Andromeda Galaxy - Our Nearest Neighbor

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