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Astronomy 101 Planetarium Lab
Instructor: Brian Pohl
ConOps: Craig Zdanowicz
www.physics.unc.edu/~bpohl/
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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
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What is a galaxy?
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Hubble Tuning Fork
Is this a trend in evolution?
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Redshift - objects appear redder
the faster they move away from you
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Expansion of Universe
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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!
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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)
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And may I now present the final
star show of the season!!
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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??
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START NOW
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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!!
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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!!
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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
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