VIEWS OF OUR UNIVERSE UNIT: Electromagnetic Spectrum/Waves Notes Astronomy 9/22/2018

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

Types of Waves 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 9/22/2018

Characteristics of Waves 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 9/22/2018

More Characteristics of Waves 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) 9/22/2018

More Characteristics of Waves 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 9/22/2018

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 9/22/2018

Types of Interference: 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 9/22/2018

Constructive Interference Destructive Interference

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 9/22/2018

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 9/22/2018

an electromagnetic transverse wave; 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 9/22/2018

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 9/22/2018

White - the reflection of all colors together 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 9/22/2018

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) 9/22/2018

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 9/22/2018

Reflection - when waves bounce back off an object 9/22/2018

Mirrors - reflect light Law of Reflection - the angle of incidence equals the angle of reflection Lenses - refract light Mirrors - reflect light Prisms - separate light into the visible spectrum by refraction 9/22/2018

a)opaque - no light gets through 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 9/22/2018

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. 9/22/2018

A photon of light is produced whenever an electron in a higher-than-normal orbit falls back to its normal orbit. 9/22/2018

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. 9/22/2018

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. 9/22/2018

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. 9/22/2018

Cassiopeia A – supernova remnant in radio light 9/22/2018

Triangulum Galaxy in radio and visible light 9/22/2018

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. 9/22/2018

Cosmic Microwave Background Radiation taken by WMAP 9/22/2018

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%. 9/22/2018

All Sky Map of IRAS Point Sources The plane of our galaxy runs horizontally across the image. 9/22/2018

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. 9/22/2018

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. 9/22/2018

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. 9/22/2018

Galaxy M100 taken by HST 9/22/2018

Center of Galaxy Centaurus A taken by HST 9/22/2018

Galaxy Triplet Arp 274 taken by HST 9/22/2018

Star Clusters in the Large Magellanic Cloud taken by HST 9/22/2018

Quadruple Moon Transit of Saturn taken by HST 9/22/2018

A Cosmic “String of Pearls” surrounds an exploding star taken by HST 9/22/2018

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. 9/22/2018

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. 9/22/2018

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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. 9/22/2018

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. 9/22/2018

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