Unformatted text preview: Observational Astronomy The EarthMoon System The Phases of the Moon Eclipses (Solar, Lunar, partial, total, annular, umbra/penumbra) The Earth in Space Earth-Moon System Earth has a diameter ~4x Greater than Moon (8000 miles vs. 2000 miles) Earth has a volume ~50X Greater Than Moon EM distance is ~30X Earth diameter or about 240,000 Miles Moon orbits Earth in 27.5 days Moon phases cycle in 29.5 days Earth-Moon System Moon only other celestial body visited by Humans Apollo Program: 9 Lunar flights (8, 10, 11, 12, 13, 14, 15, 16, 17) 19681972 24 Astronauts made trip (3 twice) 12 Men walked on Moon Phases of the Moon One of the Most Obvious astronomical cycles Basis of the Month Same Phase seen planetwide (minor differences) Below Equator Moon inverted The Moon goes though all of its phases in about 29.5 days Solar Eclipses occur when the phase of the Moon is new. A total eclipse usually lasts less than 3 minutes. Solar Eclipses Total, Partial, or Annular Usually 2 visible per year somewhere Path is Narrow, Duration short Average Between Total Solar Eclipses at One Specific Location ~300 years Spectacular Visual Experience Based on Lunar and Solar disks of similar size Unique Phenomenon in Solar System Lunar Eclipses occur when the phase of the Moon is full. The total phase of a lunar eclipse can last up to 50 minutes. Lunar Eclipses Total or Partial Usually 2 visible per year somewhere Path is Wide, Duration Long Average Between Total Lunar Eclipses at One Specific Location ~3 years Potentially Colorful Visual Experience Based on Atmospheric conditions Interesting on Moon Also Earth in Space Earth one of 8 Major Planets Small, Rocky, Inner Planet (vs. Large, Gaseous, Outer Planet) Orbit nearly circular Average Distance from Sun of ~ 93 million miles Diameter ~1/100 of Sun Major Earth/Moon Motions Define Environment The Sky Motions and the Calendar The differences between the motions of stars versus the Sun versus the Moon versus planets are easily observed. They have Environmental and Calendrical Importance. Five major types of movement in Solar System cause what is seen in the sky and experienced on Earth: 1. Earth rotates on its axis DAY (basic rising and setting of celestial objects) 2. Earth revolves around Sun YEAR/Seasons 3. Moon revolves around Earth Month/Tides 4. Earth wobbles on axis Climate Change 5. Planets revolve around Sun (planets show motion with respect to stars) The Sun, Moon, and planets appear to move along the strip of sky defined by ecliptic (the constellations of the Zodiac are also located here). The Reasons for Seasons Winter is Colder During winter, days are shorter and the Sun heats the ground less. This is because the Sun does not get very high in the sky, and sunlight is spread over a larger area of ground. Summer, Winter, and the Tropics At local noon the Sun will be overhead on the Tropic of Cancer (latitude 23.5 deg) on the summer solstice (Northern Hemisphere) and overhead at the Equator on the equinoxes. Summer and Winter, and Fall and Spring, are switched in the Northern and Southern Hemispheres. The ecliptic plane (the constellations of the Zodiac are located here) is defined by the path of the Earth's orbit about the Sun, whereas the celestial equator is the Earth's equator projected out into space. As the Sun moves around the ecliptic it appears in front of different constellations of the Zodiac which cannot be seen because the sky is so bright Tides Tides are mainly caused by the differential gravitational force of the Moon on one side of the Earth versus the other (above right). Both the Moon (major effect) and Sun (minor effect) contribute to tides. When the Moon and Sun are in alignment there are "spring tides" (most extreme differences between high and low tide) and at the quarter Moon phases there are "neap tides" (least extreme). Tidal tables are used to accurately predicted high and low tides (left). Matter and Electromagnetic Radiation (ER) The building blocks of matter (molecules, atoms, ions) and definitions. ER is also called light and photons. Light travel time (186,000 miles/sec) is often used to express distances. Photons are wavelike particles that carry different amounts of energy: shorter wavelength = higher energy (higher frequency) longer wavelength = lower energy (lower frequency) Protons and neutrons are the building blocks of the nuclei of molecules, atoms, and ions. Matter and ER (conti) ER from low to high energy (long to short wavelength): radio waves low energy, low frequency, long wavelength IR visible: red, orange, yellow, green, blue, indigo, violet (ROY G. BIV) UV xrays gamma rays high energy, high frequency, short wavelength An ER spectrum of an astronomical object is the intensity of light versus the light's wavelength. Types of ER spectra: continuum spectrum emission line spectrum absorption line spectrum The Electromagnetic Spectrum continuum spectrum Hot gas emissionline spectrum absorptionline spectrum Cool gas Spectroscopy reveals much ... Brightness and Distance perceived brightness: called apparent magnitude (logarithmic units) intrinsic brightness: called absolute magnitude (logarithmic units) or luminosity inverse square law of light: governs how light fades away with increasing distance Let There Be Light! = wavelength = frequency
c = 3 x 108 m/s
The speed of light is the cosmic speed limit- nothing can move faster Seeing the Light
VLA MAP SIRTF EUVE Chandra G:LAST HST/Keck Basic Observational Terms Cloud Cover Percentage of sky blocked by clouds. Transparency Measure of ability of light to pass through the atmosphere. Highly dependent on moisture in the atmosphere. Seeing Measure of the stability of the atmosphere. Good seeing corresponds with stable air and stable images Averted Vision Technique for observing faint objects by viewing them off center (out of the corner of your eye) in order to focus the light on the parts of the retina that work well in low light. Radio Cool objects (0 to a few 10s Kelvin) Electrons spiraling around magnetic fields Collisionally deaccelerated or accelerated electrons Cold molecular clouds Planets pulsars Radio galaxies Intergalactic matter Microwave a bit warmer objects (10s to 100K) microwave generator warm molecular clouds Planets water masers Galaxies The Universe! Infrared warm objects (100 to about 2000 K) Nebulae Planets "Normal" stars Enshrouded protostars Galaxies Visible hot objects (2000 to about 10000 Kelvin) the Sun of course! Nebulae Planets "Normal" stars, sunlike and hotter Galaxies Ultraviolet hotter objects (10,000 to about 100,000 Kelvin) Nebulae Planets with magnetic fields (aurorae) OF stars Pulsars Galaxies X-rays very hot objects (100,000 to a few 106 Kelvin) electrons in magnetic fields electrons scattering off photons Planets O star winds solar corona White dwarfs Pulsars Black holes Galaxy clusters Dark matter, indirectly Gamma Rays Extremely energetic objects Radioactive decay (Co56, Ti44) Fusion Cosmic ray/gas interaction matter/antimatter annihilation supernovae Diffuse Galactic emission Active galaxies (some) Pulsars black holes Gamma Ray Bursts Powers of Ten Charles and Ray Eames (Video 1977) A Campus Scene 16 x 16 m (52 x 52 ft) A City View 1.6 x 1.6 km (1 x 1 mile) The Landscape of Pennsylvania 160 x 160 km (100 x 100 miles) The Earth Diameter of the Earth: 12,756 km Earth and Moon Distance Earth Moon: 384,000 km Earth Orbiting Around the Sun Distance Sun Earth = 150,000,000 km Earth Orbiting Around the Sun
In order to avoid large numbers beyond our imagination, we introduce new units:
1 Astronomical Unit (AU) = Distance Sun Earth = 150 million km (93 million miles) The Solar System Approx. 100 AU (Almost) Empty Space Around Our Solar System Approx. 10,000 AU The Solar Neighborhood Approx. 17 light years The Solar Neighborhood
New distance scale: 1 light year (ly) = Distance traveled by light in 1 year = 63,000 AU = 1013 km = 10,000,000,000,000 km (= 1 + 13 zeros) = 10 trillion km Approx. 17 light years Nearest star to the Sun: Proxima Centauri, at a distance of 4.2 light years The Extended Solar Neighborhood Approx. 1,700 light years The Milky Way Galaxy Diameter of the Milky Way: ~ 75,000 ly The Local Group of Galaxies Distance to the nearest large galaxies: several million light years The Universe on Very Large Scales Clusters of galaxies are grouped into superclusters. Superclusters form filaments and walls around voids. Telescope Optics Telescope optics collect and focus ER. Properties of Optics: collecting area of optics: depends on lens/mirror diameter and affects image brightness resolution: determines the image clarity, theoretically better with larger diameter optics (but theoretical resolution versus atmospheric blurring or "seeing" is a factor) telescope focal length: determines the image scale magnification or power is given by the telescope focal length divided by the eyepiece focal length Refracting Telescope Lens
simple refracting telescope objective lens incoming light eyepiece telescope focal length Reflecting Telescope Mirror The Keeler telescope at Allegheny Observatory Telescope Image Clarity Theoretically, image clarity is directly proportional to the diameter of the telescope lens or mirror; however, atmospheric "seeing" generally blurs optical images Telescope Optics (conti)
Refracting Telescope: uses a lens (lens may suffer from chromatic aberration) Reflecting Telescope: uses a mirror (mirror may suffer from spherical aberration) Combination Telescope: uses lenses and mirrors (e.g. Schmidt Telescope, SchmidtCassegrain Telescope) Telescope Mounts Equatorial mount: can track stars The polar axis is pointed toward the "north star" and an electric motor turns the polar axis to compensate for Earth's rotation. German equatorial mount and fork equatorial mount are the most common. Altazimuth mount: point main axis to zenith (overhead) simplest for terrestrial viewing Equatorial Telescope Mount ER is Permanently Recorded A scientific instrument replaces the eyepiece: spectrograph: records spectrum (intensity vs. wavelength) photometer: records intensity or image (overall brightness in some colored filter) A detector is placed at end of the instrument's light path: photographic plate (optical telescope) CCD (optical telescope) an antenna with a receiver (radio telescope) Modern Generation Telescope NASA's Great Observatories ("space telescopes"): Hubble Space Telescope HST (UV, optical, IR; no atmospheric blurring!) Compton Gamma Ray Observatory GRO (gamma rays) Chandra Advanced XRay Astrophysics Facility AXAF (xrays) Spitzer Space Infrared Telescope Facility SIRTF (far IR) New Generation of Large GroundBased Optical Telescopes: For example: the twin Keck 10m diameter telescopes in Hawaii they use mirror segments each are currently have the largest single diameter in the world They are beginning to employ designs to overcome atmospheric blurring New Generation of Radio Telescopes: the Very Large Baseline Array (VLBA) connects radio telescopes world wide NASA's Hubble Space Telescope being deployed by the Space Shuttle. The telescopes on Mauna Kea, Hawaii The Keck 10 meter telescopes on Mauna Kea, Hawaii Radio telescopes observe ... The 100m Greenbank Radio Telescope HI map of the Milky Way The Very Large Array Synthesis Radio Telescope ...
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This note was uploaded on 04/07/2008 for the course ASTRON 0088 taught by Professor Radzilowicz during the Spring '08 term at Pittsburgh.
- Spring '08