Light, Astronomical Observations, and the

Sun

Terms

• Spectrum– A range of something, e.g. colors

• Spectra– Plural of spectrum

• Incandescent– Hot enough to glow (emit visible light

radiation)

Terms

• Wavelength (λ)– Length of one wave from peak to peak

– Shorter wavelength = more energy

– For visible light• Shorter wavelength = BLUE• Longer wavelength = RED

Terms

• Light-year– Distance traveled by light in one year– 5,900,000,000,000 miles– Measure of distance, not time

Light, Astronomical Observations, & the Sun

• Signals From Space

• Spectroscopy

• The Doppler Effect

• Optical Telescopes

• Radio and Orbiting Telescopes

• The Structure of the Sun

PSCI 131: Light, Astronomical Observations, & The Sun

Signals from Space

• The electromagnetic (EM) spectrum

– Energy waves (radiation) emitted by matter

PSCI 131: Light, Astronomical Observations, & The Sun

The EM SpectrumPSCI 131: Light, Astr. Observations, & The Sun – Signals from Space

EM Radiation from Celestial Objects

• EM energy is emitted from many objects– Stars– Black holes– Supernovae (exploding stars)– Etc.

• Not the same as reflected energy– Moons, planets, etc. reflect energy from stars

PSCI 131: Light, Astr. Observations, & The Sun – Signals from Space

EM Radiation from Celestial Objects

• Emitted radiation can be collected and used to study the object

– Telescopes: optical, radio, space-based

– Spectroscopy

PSCI 131: Light, Astr. Observations, & The Sun – Signals from Space

Spectroscopy

PSCI 131: Light, Astr. Observations, & The Sun

Spectroscopy• Using radiation from an object to learn about

that object

• Most astronomical observations can only use radiation– Most objects too far away to visit

PSCI 131: Light, Astronomical Observations, & The Sun

Visible Light Spectra• Visible light can be split into its component

wavelengths (colors)

• Creates continuous, bright-line, and dark-line spectra

• Spectra can give key information about the object the light came from

PSCI 131: Light, Astronomical Observations, & The Sun - Spectroscopy

Visible Light SpectraPSCI 131: Light, Astronomical Observations, & The Sun - Spectroscopy

(Low-temp) (Incandescent)

CONTINUOUS DARK-LINE BRIGHT-LINE

Visible Light Spectra• Visible light can be split into its component

wavelengths (colors)

• Creates continuous, bright-line, and dark-line spectra

• Spectra can give key information about the object the light came from

PSCI 131: Light, Astronomical Observations, & The Sun - Spectroscopy

Continuous Spectrum

• Shows surface temperature of object

• Shows total energy emitted by object

PSCI 131: Light, Astronomical Observations, & The Sun - Spectroscopy

Continuous Spectrum Shows Surface TempPSCI 131: Light, Astronomical Observations, & The Sun - Spectroscopy

COOLER HOTTER

Continuous Spectrum Shows Total Energy

• Proportional to fourth power of object’s surface temperature

– Example: if Star B is twice as hot as Star A…

– …Star B emits 2 x 2 x 2 x 2 = 16 times more energy that Star A

PSCI 131: Light, Astronomical Observations, & The Sun - Spectroscopy

Dark-Line SpectrumPSCI 131: Light, Astronomical Observations, & The Sun - Spectroscopy

• Light from star’s interior passes through gas composing star’s exterior

Exterior gases

Interior

Dark-Line SpectrumPSCI 131: Light, Astronomical Observations, & The Sun - Spectroscopy

From: mail.colonial.net 

• Shows what elements are present in object

• Each element absorbs a unique pattern of visible light wavelengths

Dark-Line SpectrumPSCI 131: Light, Astronomical Observations, & The Sun - Spectroscopy

From: mail.colonial.net 

• Shows what elements are present in object

• Each element absorbs a unique pattern of visible light wavelengths

Bright-Line Spectrum• Shows what elements are present in object

• Each element emits a unique wavelength pattern when heated

PSCI 131: Light, Astronomical Observations, & The Sun - Spectroscopy

From: intro.chem.okstate.edu

The Doppler Effect

PSCI 131: Light, Astr. Observations, & The Sun

Sheldon’s Doppler Effect costume

The Doppler Effect• Apparent shift in wavelength relative to a

stationary observer

PSCI 131: Light, Astronomical Observations, & The Sun – Doppler Effect

The Doppler Effect with sound waves. Longer apparent wavelength = lower frequency.

Red and Blue Shift

• Light waves undergo Doppler Effect

PSCI 131: Light, Astronomical Observations, & The Sun – Doppler Effect

Red/Blue Shifts Change Dark-Line Spectra

• Star moving away from Earth = RED shift

• Star approaching Earth = BLUE shift

PSCI 131: Light, Astronomical Observations, & The Sun – Doppler Effect

Optical Telescopes

PSCI 131: Light, Astr. Observations, & The Sun

Optical Telescopes• Gather visible light radiation

• Concentrate it at a focal point, creating magnified image

• Two types– Refracting– Reflecting

PSCI 131: Light, Astr. Observations, & The Sun – Optical Telescopes

Optical Telescopes: RefractingPSCI 131: Light, Astr. Observations, & The Sun – Optical Telescopes

From: www.odec.ca 

Optical Telescopes: Refracting• Advantages

– Inexpensive– Lens doesn’t have to be perfect to make a decent

image

• Drawbacks– Chromatic aberration reduces image quality, limits

maximum telescope size– Chromatic aberration: “halo” of color around image

caused by refracted light

PSCI 131: Light, Astr. Observations, & The Sun – Optical Telescopes

Optical Telescopes: ReflectingPSCI 131: Light, Astr. Observations, & The Sun – Optical Telescopes

From: odec.ca

Optical Telescopes: Reflecting• Advantages

– No chromatic aberration– Can be very large, so higher magnification

• Drawbacks– More expensive– Tiny flaws in mirror can greatly reduce image

quality

PSCI 131: Light, Astr. Observations, & The Sun – Optical Telescopes

From: www.odec.ca 

Radio & Orbiting Telescopes

PSCI 131: Light, Astr. Observations, & The Sun

Radio Telescopes• Gather radio waves from space

• These signals are extremely faint

• Collecting dish must be very large

PSCI 131: Light, Astr. Observations, & The Sun – Radio & Space Telescopes

Radio Telescopes

PSCI 131: Light, Astr. Observations, & The Sun – Radio & Space Telescopes

From: amazing-space.stsci.edu 

Radio Telescope at Arecibo, Puerto RicoPSCI 131: Light, Astr. Observations, & The Sun – Radio & Space Telescopes

World’s largest & most sensitive R.T.

Diameter: 1000 ft

Depth: 167 ft

Weight of receiver: 900 tons

Orbiting Telescopes• Optical, radio, gamma-ray, X-ray, infrared

• No atmospheric or human “noise”

PSCI 131: Light, Astr. Observations, & The Sun – Radio & Space Telescopes

The Hubble Space TelescopePSCI 131: Light, Astr. Observations, & The Sun – Radio & Space Telescopes

Type: Reflecting

Years in operation: 24

Orbit height: 347 miles

Orbital speed: 25,000 ft/sec

Length: 43 ft

Mirror diameter: 7.9 ft

Farthest object observed:

13 billion light years away

From: nasa.gov

(76,700,000,000,000,000,000,000 miles)

Structure of the Sun

PSCI 131: Light, Astr. Observations, & The Sun

The Sun’s Composition• Form: gaseous

• Density: slightly greater than water

• Hydrogen: 90%

• Helium: almost 10%

• Other trace elements: less than 1%

PSCI 131: Light, Astr. Observations, & The Sun – The Sun

The Sun’s Emissions

• The sun emits two things into space:

– Radiation, including visible light

– Solar wind, streams of protons & electrons

PSCI 131: Light, Astr. Observations, & The Sun – The Sun

The Sun’s LayersPSCI 131: Light, Astr. Observations, & The Sun – The Sun

Modified from: visual.merriam-webster.com

1. CORONA

2. CHROMOSPHERE

3. PHOTOSPHERE

5. RADIATION ZONE

4. CONVECTION ZONE

6. CORE

Numbers are in order of increasing depth

PSCI 131: Light, Astr. Observations, & The Sun – The Sun’s Layers

From: mreclipse.com

Corona (during solar eclipse)

PSCI 131: Light, Astr. Observations, & The Sun – The Sun’s Layers

From: astroguyz.com

Chromosphere

PSCI 131: Light, Astr. Observations, & The Sun – The Sun’s Layers

From: www.astronomynotes.com

Photosphere: closeup view

Source of visible light

Covered by granules

produced by convection

“Boiling” appearance

Movie: Visiting the photosphere for one hour

The Sun’s Engine

• Matter is converted to energy in the core

• Nuclear fusion reactions

• Hydrogen + hydrogen = helium + energy– 4 billion tons per second

• E = mc2

c: speed of light (186,000 miles/second)

PSCI 131: Light, Astr. Observations, & The Sun – The Sun

End of Light & The Sun Chapter