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The Transient Sky Things that move, change brightness or color Solar System Stars, planets, gas in our own Galaxy Other galaxies Tides and Moon Phases Water stretches much more than rock water tides bigger Moon much CLOSER than Sun Moon’s tides twice as strong as Sun's Moon over same spot on Earth every 25 hrs time of high tide changes daily 1st,3rd qtrs (weaker) new (strongest) Tides caused by Earth’s shape deforming as it rotates: 2 high and 2 low tides every 25 hours -- linked to powerful earthquakes! full Precession • Earth: equatorial bulge – (equator spins faster than poles) • Moon's orbit inclined to ecliptic by 5º, thus to equator by 18-28°, pulls on bulge Astrology doesn’t account for precession – Effect: like sideways spinning in a tilted top – One full sideways spin: 26,000 years • Effect: North Star changes, spring constellations become summer constellations etc. • Similar process causes Moon’s libration (wobbling) Lunar Libration (seen from Earth) From Earth, we see 59% of moon’s surface • (1) Seeing moon from opposite sides of Earth every 12 hrs, (2) elliptical orbit (variable orbital speed), (3) orbit inclined to Earth’s equator cause libration (N-S “nodding”) Fig. 10-3, p. 229 10.2b Solar Dynamo: winding magnetic field and sunspot numbers Little Ice Age Cooling 150 yrs Fig. 10-18b, p. 237 Prominence Eruption Fig. 10-8a, p. 231 Planetary Motion We observe Mercury, Venus, Mars, Jupiter and Saturn moving among the “fixed stars” around the sky: video Some motion is “retrograde” (backward) confused our ancestors – led to change our view of Universe Earth is NOT the center! video Asteroids & Comets Asteroids are EVERYWHERE! video Comets also are all over – with DIFFERENT orbits! video Near-Earth asteroids Chance to study some up close with radar Osiris-Rex sample return Collision warnings! video Barringer Crater, Arizona Diameter 0.7 mi, 50000 yrs old Impactor: iron-nickel, 50yd diameter, 300000 tons Estimated speed: 27,000 mph Explosion: 150x Hiroshima Meteorite melted, scattered See www.barringercrater.com/science Chicxulub: result of 1215km Near Earth Object -- 65 Myr old -- crater 200km wide -- Left iridium layer The dinosaur-killer! Fig. 8-28, p. 202 Pluto’s Discovery Plates 1930 Dates Jan 23 & Jan 29, 1930, moved about 1.4 arcmin (width of a pea at 10 yards) Fig. 8-2, p. 186 Can you spot Eris? Images taken over 3 hrs on 21 Oct 2003 mag=18.7, taken with Caltech 1.2m Oschin (Mt. Palomar) Schmidt Motion is 1.75 arcsec/hr (width of a BB at 10 yards/day) Don’t feel bad if you can’t see it – a computer found it Kuiper Belt Objects Comets are out there, too! Fig. 8-8a, p. 191 Beyond Pluto+Eris- you can help! Kuiper Belt – “outer asteroid belt” of icy/rocky objects, beyond Neptune Some objects appear “thrown” by unseen, massive object Need human eyes to look for moving objects! Backyard Worlds: Planet 9 Stars+Planets Beyond Solar System Q. If Earth moves around sun, why not see stars move over year? A. The stars are too far away to see motion easily! If sun were marble Earth would be pinhead 1m away next star a marble in Indianapolis Move 1 arcsecond (1 pinhead’s width at a distance of a mile) over 6 months “Parallax” motion detected with invention of photography, 1830s Parallax over 1 Year Fig. 11-8a, p. 250 Proper Motion Normally <1 arcsec/yr, often << 1 arcsec/yr Fastest: Barnard’s Star (7.1 arcsec/yr) (~8 arcmin or ~¼ diameter of Moon in a human lifetime) α Cen (nearest star system): ~3.6 arcsec/yr Need DISTANCE to convert to km/s Barnard’s star: moves 50 arcsec (width of Jupiter) in 7 years Proper Motion of Big Dipper 22º 100,000 BC to 100,000 AD Proto-planetary disks Systems are bright in IR due to blackbody emission from cool dust. HL Tau, ALMA (mm image) HL Tau, HST Herbig-Haro Objects: Jet trails from proto or premain-sequence-stars Like water splashes back from pouring water too fast down a drain: Gas spirals into a forming star Gas heats up as it's compressed Central pressure shoots it out the poles Video explanation Herbig-Haro (HH) 30, from Hubble, IR Visible light: jets bright, star invisible! Jets strike interstellar gas, make it glow Pre-main sequence HH30, HST, star (hidden by dust) visible light Shock waves: when a blob of gas hits another blob of gas supersonically HEAT + LIGHT! Fig. 12-8, p. 280 11.7 Variable Stars dec +10° N 0° E -10° -20° RA 3h 2h 1h 0h Variable Stars Stars vary for all sorts of reasons Periods from <1 hour to years Eclipsing binaries Intrinsical variables (many classes) Some regular, others irregular Mira: giant pulsating star RR Lyraes – measure distances to star clusters, map out our Galaxy Cepheids – measure distances to galaxies Interacting binaries = novae Exploding stars = supernovae Variable Stars Rev. David Fabricius, German, 1564-1617 P=331 days Naked eye Need telescope Fig. 11-26, p. 264 Light curve of Mira, 1st known variable (1596 by Fabricius) Eclipsing Binaries: inclination i~0°: since we know i ACTUAL masses (rare: ~200 known) Primary: hotter star Secondary: cooler star Partial eclipses Total eclipse Velocities + eclipse curves give relative stellar radii! Primary eclipse Secondary eclipse Flat-bottomed light curves: smaller star totally eclipsed. Round-bottomed light curve: both stars partially eclipsed. Eclipse type depends on inclination. Fig. 11-22, p. 261 Eclipsing Binary light curve From light curve and radial velocity curve (not shown), we can calculate stars’ radii, relative temperatures, combined masses and mass ratios Transiting Planets – like Eclipsing Binary Stars Planet transiting star dip in star brightness of ~0.01-1% ex: DJupiter~0.1DSun, so AJupiter/Asun~(0.1)2=0.01 -> Jupiter would block out 1% of Sun’s light if aliens watched it transit If we see planet transiting its star MUST have inclination i~0 deg if we know true velocity get accurate mass! Advantage: distance-independent! Kepler 10°x10° field Citizen Science: Find Exoplanets Planet Hunters Tutorial video Period-Luminosity Relation for Cepheid Video explanation Variables Bright stars, visible in our and other galaxies Measure period -> absolute mag. Apparent + absolute mag -> DISTANCE Good standard candles! Fig. 11-28, p. 265 Hubble key project: pick out Cepheids in other galaxies -> distances Fig. 11-30, p. 266 Mass Transfer onto White Dwarf 50% (or more) of stars in binary systems One becomes white dwarf first; lower mass star become red giant later Lower mass secondary star (red giant, weak gravity) loses mass to white dwarf (strong gravity) How a Nova Flares Up Light Echoes: V838 Monocerotis over 2.4 years 1.2pc or 41" V838 Mon, HST, blue-green-red light 2.1pc or 71" ----- Progressively larger shells of gas and dust are illuminated as light goes out from nova in all directions. In outburst, central star brightened 600,000x (14.4 mag) and swelled to as big as Jupiter's orbit. Then it faded. Distance to V838 Mon is about 6.1 kpc (6100 pc) Fig. 13-12, p. 303 Supernovae Two main types physically D = 24Mpc Core collapse (IMPORTANT): Core Collapse: explosion of supergiant star Explosion of white dwarf (WD) NASA Swift satellite A supernova can briefly shine as bright as an entire galaxy (10 billion stars!) White Dwarf Supernova Video Core Collapse Supernova Normal galaxies: bright nuclei because lots of stars in small volume Gravity pulled gas to center lots of star formation happened normal galaxy Quasars and Active Galaxies Some galaxies: unusually bright nuclei in optical/IR – and X-rays/UV/radio active galaxy Fig. 17-1a, p. 400 Active Galaxy Centaurus A optical X-ray – shows jet Fig. 17-4a, p. 401 Active Galaxy Jets Blow Bubbles in Surrounding Medium Large Synoptic Survey Telescope (LSST) First stone laid 2015 Apr 14 Standalone telescope project LSST Key Points Top-ranked major ground-based facility by NRC’s Astronomy & Astrophysics decadal survey, 2010 Video introduction to LSST NSF will pay for construction, operation Data analysis paid for by LSST Corp: 30-40 universities and research labs in US and rest of world 8 KY universities joined in 2016: UL, UK, EKU, NKU, Morehead St., Murray St., Bellarmine U, Berea College Solar Eclipses: Earth goes into Moon's shadow Next total solar eclipses from US: 21 Aug 2017 (Oregon-S Carolina) 08 Apr 2024 (Texas-Maine) 23 Aug 2044 (N DakotaMontana) 12 Aug 2045 (Cal.-Florida) Solar eclipse only happens at New Moon Solar eclipse lasts only a few minutes – Moon's shadow is much smaller than Earth Fig. 4-7, p. 69 Aug 11, 1999 solar eclipse from space From Mir space station. Shadow moves 2000 mph. Only observers near center of shadow see total eclipse. Those in outer shadow see partial eclipse. Video description Longer video Great 2017 Eclipse! Eclipse in KY: about 1pm CDT The greatest 2 minutes in astronomy! Stages of Eclipse Partial – few minutes Totality – 2 minutes Partial – few minutes Eclipse Special Effects Diamond Ring – 1st/last bit of sun appears Baily’s Beads – see bits of sun through moon’s mountains How to View Eclipse Eclipse glasses – cost a $1-few Pinhole or Binocular Projection More expensive solar projector How to photograph Eclipse Use a tripod! ONLY during totality: OK to take a normal picture OUTSIDE of totality: use a filter! See eclipse.gsfc.nasa.gov (Goddard Space Flight Center) Deluxe Photography Glass solar filter on telescope or camera Don’t Miss Eclipse for Photos! Enjoy your first experience! Some Future Total Eclipses: 2019 Jul 2: northern Chile, Argentina 2020 Dec 14: southern Chile, Argentina 2024 Apr 8: Mexico-Texas-IndianaQuebec 2044 Aug 23: North Dakota-MontanaAlberta 2045 Aug 12: California-Florida (coastto-coast)