Published on April 22, 2009
The Distance Ladder LACC §18.3, 19.1, 19.5 • Within the Solar System • Within the Galaxy • Within the Universe An attempt to answer the “big questions”: What is out there? How big is the universe? Thursday, April 22, 2010 1
Stellar Parallax (Distance Ladder) http://www.astro.umd.edu/educationalresources/astro/sprop/parallax.html Thursday, April 22, 2010 2
Stellar Parallax: Hipparcos Hipparcos is an acronym for HIgh Precision PARallax COllecting Satellite. Appropriately the proununciation is also very close to Hipparchus, the name of a Greek astronomer who lived from 190 to 120 BC. By measuring the position of the Moon against the stars, Hipparchus was able to determine the Moon's parallax and thus its distance from the Earth. He also made the ﬁrst accurate star map which lead to the discovery, when compared with other data from his predecessors, that the Earth's poles rotate in the sky, a phenomenon referred to as the precession of the equinoxes. ...distances accurate to ... 10%. For a typical measurement accuracy of 1 milliarcsec, this will mean stars with parallaxes ... 10 milliarcsec, i.e. stars within ... 100 pc of the Sun. http://www.rssd.esa.int/index.php?project=HIPPARCOS&page=FAQ Thursday, April 22, 2010 3
The Closest Stars http://calgary.rasc.ca/stellarmagnitudes.htm Thursday, April 22, 2010 4
HR Diagram http://outreach.atnf.csiro.au/education/senior/astrophysics/stellarevolution_hrintro.html Thursday, April 22, 2010 5
Main Sequence Fitting (a type of Standard Candle) If you have a cluster of stars of unknown distance, you can compare how bright the stars on its main sequence appear with how bright the stars in a cluster of known distance appear. In the example above, the stars in the Pleiades (an open cluster) are 7.5 times dimmer than the stars in the Hyades (also an open cluster), and so must be further away.You can use the inverse-square law (apparent brightness = true luminosity / 4 pi R2) to show that the Pleiades is sqrt(7.5) times further away than the Hyades. http://www.bramboroson.com/astro/apr29.html Thursday, April 22, 2010 6
Variable Stars (a type of Standard Candle) http://www.mhhe.com/physsci/astronomy/arny/instructor/graphics/ ch13/1312.jpg Thursday, April 22, 2010 7
Variable Stars (a type of Standard Candle) disregard the colors in these diagrams http://abyss.uoregon.edu/~js/ http://astronomy.nmsu.edu/ ast122/lectures/lec15.html tharriso/ast110/class22.html Thursday, April 22, 2010 8
The Distance Ladder LACC §18.3, 19.1, 19.5 • Within the Solar System: Radar Ranging • Within The Galaxy: Stellar Parallax, Main- Sequence Fitting (aka Spectroscopic Parallax), Cepheid Variable • Within the Universe: Tully-Fisher Relation, Type Ia Supernova, Brightest Cluster Galaxy, Hubble’s Law An attempt to answer the “big questions”: What is out there? How big is the universe? Thursday, April 22, 2010 9
LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch 18, pp. 413: 5 (choose your answers from the following: standard candle using main sequence ﬁtting, radar ranging, standard candle using RR Lyrae and Cepheids’ period luminosity relation, stellar parallax). • Ch 20: Tutorial Quizzes accessible from: www.brookscole.com/cgi-brookscole/course_products_bc.pl? http:// ﬁd=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due at the beginning of the next class period. Thursday, April 22, 2010 10
The Interstellar Medium LACC §18.3, 19.1, 19.5 • Nebulae • Dust • Gas An attempt to answer the “big questions”: What is out there? How big is the universe? Thursday, April 22, 2010 11
Where did all the stars go? What used to be considered a hole in the sky is Molecular Cloud now known to astronomers as a dark molecular cloud. Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars. The eerily dark surroundings help make the interiors of molecular clouds some of the coldest and most isolated places in the universe. One of the most notable of these dark absorption nebulae is a cloud toward the constellation Ophiuchus known as Barnard 68, pictured above. That no stars are visible in the center indicates that Barnard 68 is relatively nearby, with measurements placing it about 500 light-years away and half a light-year across. It is not http://apod.nasa.gov/apod/ap041219.html known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely Note: molecular clouds are places for new stars to form. It is dark in color. Why? possible to look right through the cloud in infrared light. Thursday, April 22, 2010 12
HII Regions M42 Orion Nebula and NGC1977 Note: HII regions are reddish in color. Why? http://autostarsuite.net/photos/snoleopard/picture3566.aspx Thursday, April 22, 2010 13
Orion: Visible vs. Infrared Betelgeuse Orion Nebula Rigel http://www.compadre.org/informal/features/featureSummary.cfm?FID=642 Thursday, April 22, 2010 14
Planetary Nebula aka The Saturn Nebula http://www.ucl.ac.uk/star/research/stellarenvironment/cieresearch/planetarynebulae Thursday, April 22, 2010 15
Reﬂection Nebula Note: reﬂection nebula are bluish in color. Why? Unspeakable beauty and unimaginable bedlam can be found together in the Triﬁd Nebula. Also known as M20, this photogenic nebula is visible with good binoculars towards the constellation of Sagittarius. The energetic processes of star formation create not only the colors but the chaos. The red-glowing gas results from high-energy starlight striking interstellar hydrogen gas. The dark dust ﬁlaments that lace M20 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions. Which bright young stars light up the blue reﬂection nebula is still being investigated. The light from M20 we see today left perhaps 3000 years ago, although the exact distance remains unknown. Light takes about 50 years to cross M20. http://apod.nasa.gov/apod/ap070813.html Thursday, April 22, 2010 16
Supernova Remnant SN 1006 Supernova Remnant A new star, likely the brightest supernova in recorded human history, lit up planet Earth's sky in the year 1006 AD. The expanding debris cloud from the stellar explosion, found in the southerly constellation of Lupus, still puts on a cosmic light show across the electromagnetic spectrum. In fact, this composite view includes X-ray data in blue from the Chandra Observatory, optical data in yellowish hues, and radio image data in red. Now known as the SN 1006 supernova remnant, the debris cloud appears to be about 60 light-years across and is understood to represent the remains of a white dwarf star.... Because the distance to the supernova remnant is about 7,000 light-years, that explosion actually happened 7,000 years before the light reached Earth in 1006. http://apod.nasa.gov/apod/ap080704.html Thursday, April 22, 2010 17
The Local Bubble http://www.sslmit.unibo.it/zat/images/ cartography/M-Way_2.htm Thursday, April 22, 2010 18
Dust Grains A cosmic dust cloud sprawls across a rich ﬁeld of stars in this gorgeous wide ﬁeld Very small solid particles or "dust grains"; telescopic vista looking toward Corona smoke-like. These absorb and redden Australis, the Southern Crown. Probably light passing through them. less than 500 light-years away and Absorption by dust creates "dark clouds" effectively blocking light from more seen against bright sources such as the distant, background stars in the Milky Way, Milky Way. the densest part of the dust cloud is about 8 light-years long. http://www.astro.virginia.edu/ class/oconnell/astr121/ http://antwrp.gsfc.nasa.gov/ guide11.html apod/ap040715.html Thursday, April 22, 2010 19
Dust Grains The grains appear to be loose conglomerations of smaller specks of material, which stuck together after bumping into each other in the depths of space. http://spiff.rit.edu/classes/phys230/lectures/ism_dust/ism_dust.html Thursday, April 22, 2010 20
The Interstellar Medium LACC §18.3, 19.1, 19.5 • Nebulae: Dark Dust Clouds (aka Molecular Clouds), HII Regions (e.g. star-forming regions, planetary nebulae; HII emission line), Reﬂection Nebulae (reﬂection off dust), Supernova Remnants • Dust: 1 grain / 1012 atoms; silicates, carbon, ices • Gas: 90% H, 9% He, 1% heavier (by number); 1 atom / cm3 (1000 / cm3 is an excellent laboratory vacuum), 100 Kelvin (but varies) An attempt to answer the “big questions”: What is out there? How big is the universe? Thursday, April 22, 2010 21
LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch 19, p. 435: 13, 14. • Ch 21: Tutorial Quizzes accessible from: http:// www.brookscole.com/cgi-brookscole/course_products_bc.pl? ﬁd=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due at the beginning of the next class period. Thursday, April 22, 2010 22
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