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Science A-36 Brief Overview and Intro (for those not in Tues. class…)

Science A-36 Brief Overview and Intro (for those not in Tues. class…). Welcome to A-36! Course Staff: Professor Jonathan (“Josh”) Grindlay Jaimie Pineda (TF) Josh Younger (TF) Sam Quinn (Clay Telescope & Astro. Lab mgr.). What’s A-36 all about?. Seeing Stars!

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Science A-36 Brief Overview and Intro (for those not in Tues. class…)

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  1. Science A-36 Brief Overview and Intro(for those not in Tues. class…) Welcome to A-36! Course Staff: Professor Jonathan (“Josh”) Grindlay Jaimie Pineda (TF) Josh Younger (TF) Sam Quinn (Clay Telescope & Astro. Lab mgr.) Sept. 20, 2007

  2. What’s A-36 all about? Seeing Stars! Observing, and actually measuring the building blocks of the Universe From the closest, the Sun To the nearby young stellar cluster, the Pleiades To star birth in Orion And death in the Crab nebula and neutron star And on to huge assemblies of stars, Galaxies Sept. 20, 2007

  3. Dense star field in Milky Way Sept. 20, 2007

  4. Telescope image of Sun, with sunspots Sept. 20, 2007

  5. Sept. 20, 2007

  6. Orion nebula: stellar nursery… Sept. 20, 2007

  7. Crab Nebula: remnant of Supernova in 1054AD Sept. 20, 2007

  8. A spiral galaxy (M62; at d = 10Mpc ~35Mly) that is much like our own Milky Way Galaxy and contains ~1011 stars Sept. 20, 2007

  9. A-36 Evelabs will obtain and measure images of these objects with the new Clay Telescope A “professional” 16in computer-controlled telescope, on Science Center roof… Sept. 20, 2007

  10. And in Daylabs we will measure the Sun with a Heliostat outside the 8th Floor Astro Lab…. Which beams the solar image into the Astrolab from a Tracking mirror outside to then reflect off 2 fixed mirrors in the lab to give an image or input to a spectrograph Sept. 20, 2007

  11. Allowing us to conduct some fundamental measurements of the Sun in Daylabs • Using a sun dial to measure the march of the seasons and the actual radius of the Sun • Measure Sun’s diameter in red vs. blue filters and deduce temperature structure of solar atmosphere • Measure Sun’s rotation velocity and period and deduce the size of our Solar system, and so distance yardstick to the stars Sept. 20, 2007

  12. How is A-36 “run”? • Two class meetings/week (lecture and discussions) to understand the stars and the readings • Readings typically 1 chapter/week in assigned textbook Universe: Stars and Galaxies (Freedman and Kaufmann; 3rd ed.) • Two lab meetings/week (DayLab and Evelab), ea. 1h, for hands-on actual observations. “Sections” if cloudy What background/skills required? None! Course will use simple algebra, and explain all… Sept. 20, 2007

  13. See Syllabus for details…and fill out Lab Section Preference Form (in class; or email us the form) • Learning style – hands on (unique in Core…) • Workload – not bad; 1 “extra” hour/week of lab… • Grading – Labs, final, midterm, participation, quizes • Labs (Evelab and Daylab): section signup in Today’s class (pls. fill out form; OR download from website and email it to squinn@cfa.harvard.edu Sections announced on class website by next MONDAY when labs begin. Sections “fine-tuned” next week… • OPEN HOUSE for Daylab (right after class today, SC804) and for Evelab (TONIGHT, and Thurs.) 730-9pm on Science Ctr. roof top (8th floor; then 2 flights up stairs) to Clay Teles. Sept. 20, 2007

  14. Distance to Sun and Stars: Large… • Astronomy is a “remote” observation and measurement science; can’t “go there” and study stars up close. • But… we can measure (even precisely) physical distances, sizes, masses and composition of stars: the parsec (pc) is distance at which star’s parallax moves it by 1arcsec as viewed over 3months. See Fig.: Definition: 1pc = 1AU/1” = 3 x 1018cm • Closest star (Proxima Cen) is at distance d = 1.3pc = 4.3lightyears = distance light travels at 186,000miles/sec over 4.3 years, given that 1 year = 3 x 107sec: d = 1.86 x 105 x 4.3 x 3 x 107 = 2.40 x 1013 miles = 3.93 x 1013 km = 3.93 x 1018cm Sept. 20, 2007

  15. Astronomically large distances and numbers… • Earth at mean distance from Sun of 1 Astronomical Unit = 1 AU = 1.5 x 108 km = 1.5 x 1013 cm, which you will actually measure (approx.) in Daylab 3 • Closest star (Prox. Cen) at d = 1pc = 1AU/1arcsec, but with arcsec in radians (1” ~ 1/(2 x 105), so 1pc ~ 2 x 105 AU = 3 x 1018 cm ~ 3.3 lightyears • Pleiades cluster at d ~100pc; Crab at d ~ 2kpc; our entire Milky Way Galaxy has disk with radius ~15kpc and closest similar galaxy (Andromeda) at ~0.7Mpc Sept. 20, 2007

  16. Enough Intro… How do the Sun & Stars “move”? • Sun and stars rise in East, set in West, for their daily diurnal motion with period of Earth’s rotation, 24h • Earth orbits the Sun with period 1y; a given star (e.g. Vega) thus rises ~4min earlier each night since the Earth has moved by ~1degree since 1deg =1/360 of full circle is ~1/365 of a year and since 1deg = 4min of diurnal motion (check: 360o = 24h; so 15o = 1h…) a few figures (from your text, ch. 2) may help… Sept. 20, 2007

  17. Diurnal vs. Sidereal motion Earth’s rotation (24h) causes diurnal motion of Sun and stars, which rise earlier in Boston than in LA… Earth’s orbit around Sun (365d) causes sidereal motion of stars (and planets) which “move” at local midnight so that Summer Triangle is overhead at midnight in June vs. Orion in December, as seen from Boston Sept. 20, 2007

  18. So how do we “see” the night sky? • Stars (e.g. Vega) change in elevation (angle above horizon) as they rise and set; but in fact are rotating about north celestial pole (near Polaris) as you will measure/verify in Evelab 1 Easiest to think of a Celestial Sphere of the fixed stars, with Earth rotating “underneath”. You will deduce this from Simple elevation measurements over 2 weeks of Vega, Big Dipper star and a Casseiopia star and Polaris in EL1. Sept. 20, 2007

  19. And why is summer hot? And reversed in N vs. S hemispheres? • The Earth’s spin axis is tilted by 23.5o from plane of its orbit around Sun: • Which also gives rise to changing Sun elevation you will measure in DL1 Sept. 20, 2007

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