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VIEWS OF OUR UNIVERSE UNIT:

Electromagnetic Spectrum/Waves Notes

Astronomy

Wave – a rhythmic disturbance that carries energy through matter or space

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Transverse Wave - a wave that vibrates perpendicular to the direction of the wave’s motion

Longitudinal Wave - a wave that vibrates parallel to the direction of the wave’s motion

Types of Waves

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Crest - the high points of a wave

Trough - the low points of a wave

Amplitude(A) - the distance from the midpoint of a wave to its crest or trough

Characteristics of Waves

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Wavelength (λ) - the distance between two consecutive points on a wave (ex: crest to crest)

Frequency (f) - the number of waves that pass a given point in one second, measured in Hertz(Hz)

More Characteristics of Waves

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Rarefaction - part of a longitudinal wave where the molecules are spread farther apart

Compression - part of a longitudinal wave where the molecules are closer together

More Characteristics of Waves

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Speed of a wave : v=f λ (velocity= frequencyXwavelength)

Interference of waves - when two or more waves combine they combine to form a new wave

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Constructive Interference - when two or more waves combine to make a bigger wave than the original ones

Destructive Interference - when two or more waves combine to make a smaller wave than the original ones

Types of Interference:

Constructive Interference

Destructive Interference

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Sound - longitudinal waves produced by the vibration of objects, the speed of sound depends on the elasticity of the medium it travels through and the temperature of the medium it travels through

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Sound (again) - speed of sound in room temperature air is 340 m/s, sound travels faster in liquids than in gases and faster in solids than in liquids

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Light – an electromagnetic transverse

wave; it travels in a straight line at

3X108 m/s in space; each type of light has a different

wavelength with gamma rays the shortest wavelength and radio waves the longest

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There are seven types of light (in order from the longest wavelength to the shortest):Radio Waves, Microwaves, Infrared Waves, Visible Light (red, orange, yellow, green, blue, indigo, violet), Ultraviolet Light, X-Rays, Gamma Rays

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Visible Spectrum - the part of light we can see; made of seven colors ROY G BIV (red, orange, yellow, green, blue, indigo, violet)

White - the reflection of all colors together

Black - absorption of all colors together

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Primary Colors of Light - red, green, blue (when you mix these you get white light)

Primary Colors of Pigments(things that absorb certain colors and transmit others) - yellow, cyan, magenta (when you mix these colors you get black)

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Polarization - when light can only travel/vibrate in one direction

Refraction - the bending of waves as they go from one medium to another

Diffraction - the bending of waves around objects

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Reflection - when waves bounce back off an object

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Law of Reflection - the angle of incidence equals the angle of reflection

Lenses - refract lightMirrors - reflect lightPrisms - separate light into

the visible spectrum by refraction

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Types of Objects:–a)opaque - no light gets through

–b)translucent - some light gets through but no image

–c)transparent - all light gets through so an image is seen

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How Objects Produce Light An electron has a

natural orbit that it occupies, but if you energize an atom you can move its electrons to higher orbitals.

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A photon of light is produced whenever an electron in a higher-than-normal orbit falls back to its normal orbit.

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During the fall from high-energy to normal-energy, the electron emits a photon -- a packet of energy -- with very specific characteristics. The photon has a frequency, or color, that exactly matches the distance the electron falls.

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How We “See” Objects in Light Other Than Visible

Telescopes are connected to computers that take the light they receive, calculate the amount of light coming from a specific area, and translate that light intensity into color. The computers then generate pictures we can see using the information the telescopes provided on the light intensity.

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Radio Astronomy Radio waves are given off by many

astronomical objects. They are very long waves that can penetrate gas and dust clouds in space allowing us to “see” behind nebula we would not be able to with visible light. Radio waves also penetrate into our atmosphere with little interference. Two of the most well-known radio telescopes are the VLA and Arecibo.

04/22/23 27Cassiopeia A – supernova remnant in radio light

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Triangulum Galaxy in radio and visible light

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Microwave Astronomy Microwaves are produced by many

objects in space. They do not penetrate into our atmosphere easily though. We must put probes and satellites into space to observe the microwaves produced by celestial objects. Microwave astronomy is mostly used to study the microwave radiation given off at the Big Bang called cosmic microwave background radiation.

04/22/23 30Cosmic Microwave Background Radiation taken by WMAP

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Infrared Astronomy Infrared Astronomy is the detection and study

of the infrared radiation (heat energy) emitted from objects in the Universe. All objects emit infrared radiation. Only since the early 1980's have we been able to send infrared telescopes into orbit around the Earth, above the atmosphere which hides most of the Universe's light from us. The first of these satellites - IRAS (Infrared Astronomical Satellite) - detected about 350,000 infrared sources, increasing the number of cataloged astronomical sources by about 70%.

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All Sky Map of IRAS Point Sources The plane of our galaxy runs horizontally across the

image.

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In space, there are many regions which are hidden from optical telescopes because they are embedded in dense regions of gas and dust. However, infrared radiation, having wavelengths which are much longer than visible light, can pass through dusty regions of space without being scattered. This means that we can study objects hidden by gas and dust in the infrared, which we cannot see in visible light, such as the center of our galaxy and regions of newly forming stars.

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The center of our galaxy in red light (at top), near-infrared light (middle) and far-infrared (bottom). Notice the different information gathered in each light.

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Visible Light Astronomy Visible astronomy, also called optical

astronomy, encompasses all the information gathered from space that can be seen by our eyes. Until a couple of decades ago, all information gathered from space was in the visible spectrum. We can use both Earth-based and space-based telescopes to gather visible information. Because visible light will not readily pass through objects, nebulae can block our view of the visible light emitted by objects in space. The most famous optical telescope in the world is the Hubble Space Telescope.

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Galaxy M100 taken by HST

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Center of Galaxy Centaurus A taken by HST

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Galaxy Triplet Arp 274 taken by HST

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Star Clusters in the Large Magellanic Cloud taken by HST

04/22/23 40Quadruple Moon Transit of Saturn taken by HST

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A Cosmic “String of Pearls” surrounds an exploding star taken by HST

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Ultraviolet Astronomy

Because Earth’s atmosphere absorbs so much UV radiation, much of UV astronomy is now done from space and sometimes from rockets and balloons. Planets, stars and galaxies all produce UV radiation. It is UV radiation that helps us absorb vitamin D, gives us suntans, can give us sunburns, and can cause skin cancer.

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X-Ray Astronomy

Earth’s atmosphere absorbs most of the incoming x-rays from space so X-ray telescopes need to be space-based. X-rays are given off by stars (especially neutron stars) and also by the light that gets absorbed into black holes. The Chandra X-ray Observatory is the most famous x-ray telescope in use today.

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Gamma Ray Astronomy Gamma rays are absorbed by Earth’s

atmosphere so Gamma ray telescopes are space-based. Processes that produce gamma rays include cosmic ray interactions with interstellar gas, supernova explosions, and interactions of energetic electrons with magnetic fields.

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Gamma-ray bursts are short-lived bursts of gamma-ray photons, the most energetic form of light. At least some of them are associated with a special type of supernovae, the explosions marking the deaths of especially massive stars.

Lasting anywhere from a few milliseconds to several minutes, gamma-ray bursts (GRBs) shine hundreds of times brighter than a typical supernova and about a million trillion times as bright as the Sun, making them briefly the brightest source of cosmic gamma-ray photons in the observable Universe. GRBs are detected roughly once per day from wholly random directions of the sky.

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