Electromagnetic Energy waves, Astronomy, and Stars · Electromagnetic Energy waves, Astronomy, and Stars By Leslie McGourty and Ken Rideout (modified by your teacher) What is a wave?

Electromagnetic Energy waves,

Astronomy, and Stars

By

Leslie McGourty and Ken Rideout

(modified by your teacher)

What is a wave?

• A wave is a transfer of energy from one point to another via a traveling disturbance

• A wave is characterized by its wavelength, frequency, and amplitude

Why do we care about waves?

• Because the best way to learn about

astronomical objects such as STARS,

GALAXIES, AND BLACK HOLES that

are MANY TRILLIONS OF MILES

AWAY is to study the

ELECTROMAGNETIC ENERGY

WAVES THAT THEY EMIT

(give off)

Wavelength

• Distance from one crest to the next crest

(or trough to trough)

• Measured in meters

Frequency • Number of crests passing by a given point per second

• Measured in Hertz (Hz) defined to be one cycle per sec

• Equal to the inverse of the amount of time it takes one

wavelength to pass by

Electromagnetic Waves

• Waves of energy that have both electrical and magnetic properties

• Any object that is above absolute zero emits electromagnetic waves

• The entire group of waves with these properties is called the “Electromagnetic Spectrum”

• Still confused? Then click What are electromagnetic waves?

• To move onto the EM spectrum click

TYPES OF ELECTROMAGNETIC WAVES

GAMMA RAYS

• Emitted from the nuclei of atoms during radioactive decay or during high-speed collisions with particles.

• Sources: Black holes, stars, supernovae

• Gamma ray image of The

center of the Milky Way

(where a black hole

resides)

X-

RAYS

• Emitted by atoms and/or electrons after violent

collisions

• emitted when matter sucked into a black hole is

destroyed

ULTRAVIOLET RAYS

• Above the color violet

• Three groups - UV A, UV B, and UV C.

• “A” type: longest wavelength; least harmful

• UV B and UV C are absorbed by DNA in cells

• Sources: Ultra hot objects 5000°C or more, such as Stars

• Ultraviolet energy

emitted by the sun

INFRARED

• “Below” Red visible light

• Thought of as heat but is not always

• Far infrared energy is heat energy.

• All objects that have warmth radiate infrared waves

• Easily absorbed and re-radiated.

• Used in remote controls, surveillance,

• Sources: Humans, most astronomical objects

• Infrared image of the

nucleus and coma of

comet Hale-Bopp

MICROWAVES

• 1 mm-1 dm in length

• Absorbed by water molecules – how microwave ovens heat food

• Nebulae with newly forming stars, anything with a temperature

• The microwave image

below (from COBE)

helped to prove the Big

Bang Theory

RADIO WAVES

• 10 cm- 100,000+m in length

• Only cosmic waves that reach the surface of the Earth

• Cause of “noise”

• Sources: nebulae, stars, black holes

• Radio-synthesized

image of the Crab Nebula

VISIBLE LIGHT

• White light:

combination of all the

colors

• Rainbow: white light that

has been separated into

a continuous spectrum of

colors

• Sources: very hot

objects (stars,

galaxies)

• Galaxies emit enough

visible light to be seen

from great distances

VISIBLE LIGHT PROPERTIES

VISIBLE LIGHT another view:

Stars and spectral analysis:

WHAT THE COLORS CAN TELL

US

HOW TO IDENTIFY THE COMPOSITION

OF OBJECTS • Hydrogen

• Helium

• Carbon

• Iron

When heated, each element emits its own unique and distinct pattern of

wavelengths of light. This is known as a SPECTRAL FINGERPRINT.

By using a database of these “fingerprints”, astronomers can identify the

composition of a distant object.

For example, the spectral pattern produced by a star is shown below.

It matches the spectral fingerprint of Hydrogen – therefore, we now know that

the star is composed of Hydrogen gas!

• The 3 types of spectra:

– Continuous: “solid rainbow” –

solids and ionized gases

(random electrons)

– Absorption: when white light

passes through a cool gas –

black lines appear in spectrum –

show “missing” lines – absorbed

by gas – shows gas’ identity

– Emission: by heated gases

(fingerprints)

Star Color Temperature

Star Color Size

Star Color age

WHAT COLOR IS THAT STAR?

READING THE SPECTRUM OF A

STAR

WHAT COLOR IS THAT STAR?

READING THE SPECTRUM OF A

STAR

HOW TO IDENTIFY THE COMPOSITION OF

STARS • Hydrogen

• Helium

• Carbon

• Iron

The spectral pattern produced by a star is shown

below.

It matches the spectral fingerprint of Hydrogen –

therefore, we now know that the star is composed

of Hydrogen gas!

RED AND BLUE SHIFTS: How light is

used to determine the movement of

stars

How light is used to detect “invisible” alien

planets BY OBSERVING STARS:

By measuring the cyclical Doppler shift of a star, astronomers can

figure out how far the star is wobbling, which allows them to figure

out THE MASS OF ITS ORBITING PLANET, AND ITS DISTANCE

FROM THE STAR