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Astronomy 101 Planetarium Lab Instructor: Brian Pohl ConOps: Craig Zdanowicz www.physics.unc.edu/~bpohl/ 1 Administrative Stuff • This lab is due Wednesday, April 22nd • This is the make-up lab – Final office hours on Monday and Tuesday April 20th and 21st • Final grades • Night lab evaluations 2 What is a galaxy? 3 4 5 Hubble Tuning Fork Is this a trend in evolution? 6 7 8 9 10 Redshift - objects appear redder the faster they move away from you 11 Expansion of Universe • • • • • So all objects are moving away from us Are we at the center of the universe? Raisin bread model Hubble constant - rate of recession/distance The further away galaxies are, the faster they are receding – This means the universe is expanding exponentially! 12 How Fast is the Universe Expanding? (What is the Hubble Constant?) To figure this out, you need: • Distance – You find distance by comparing apparent magnitude (or luminosity) with absolute magnitude – Standard candle gives you absolute • Velocity – You find velocity by measuring redshift • Hubble Constant – Units of: (km/s) / (Mpc) 13 And may I now present the final star show of the season!! 14 Lab Procedure • Pg. 185, data sheet pg. 191 • Measure magnitude through ‘telescope’ – (column 1) • Enter galaxy type into (column 4) • Correct the magnitude for telescope • We want to find out: – Are more distant galaxies moving faster AWAY from us?? 15 START NOW 16 1 17 2 18 3 19 4 20 5 21 6 22 7 23 8 24 What to do with all this data?? • We measured: – Brightness (Mag) in simulated telescope • We calculate: – “Actual” brightness (Mag) in ‘real’ telescope • We know: – Absolute brightness (Mag) of galaxies – Recession velocity of galaxies • We can then determine: – The distance to the galaxies • What then? – Graph Distance vs. Recession Velocity – Slope of this graph is related to expansion of Universe • Hubble Constant!! 25 Lab Write Up • 2 graphs (Do not connect dots, use best fit) – Magnitude (col 2) vs. velocity (col 7) – Distance (col 8) vs. velocity (col 7) • Find Distance from luminosity – Use absolute magnitude (col 5) and apparent (col 3) to find distance modulus – Use Figure 1 to find distance • Note: x-axis is “Apparent MINUS Absolute Magnitude” • Which graph is Hubble’s Law? – Read pages 103-104 of lab manual • Determine Hubble’s constant (also from page 103) – Use slope (Do not connect the dots, use best fit) – And percent error • can look up value online [cite source]! • Put calculations on clean sheet – Include all equations, calculations, explanations (also for finding slope) • As for error, we have been doing this all semester, here is your time to show me what you have learned!! 26 All Power Points are on my website: http://www.physics.unc.edu/~bpohl Visit office hours or email me if you have questions! [email protected] Morehead room 403 East entrance facing the arboretum. Take elevator on the right to the fourth floor. Monday 4/20: 3:00pm-5:00pm Tuesday 4/21: 5:00pm-7:00pm 27