Astronomy 101 Planetarium Lab

Instructor: Brian PohlConOps: Craig Zdanowicz

www.physics.unc.edu/~bpohl/

YOU MAY SIT WHERE YOU WISH(except for the front row and the south section)

Administrative Stuff• This is the last required lab

– Due next Wednesday (Apr .1st), no foolin!• Next lab is the Make-up Lab (optional)

– 2 weeks hence: ( Apr. 13th, 14th )– I will have my last office hours on Monday and

Tuesday Apr. 20th and 21st (see last slide for details)

– Makeup lab due Wednesday Apr. 22nd

• Evaluations at end of lab today

Measurement in Astronomy

Angles in the Sky & Time

Size of the Earth & Location on the Earth

Motions of the Planets

Night Lab Measurements– Coordinates and the Motion of Stars,

quantitatively– Relative brightness of the stars– Size of planets– Structure of the surface of the Moon– The Spectrum of Hydrogen– Perhaps the Doppler shift, again from the

Spectrum– Possibly the physics of craters and meteors

Variable Brightness

May I present the Zeiss show!!

Intrinsic variables• Changes in

brightness caused by physical changes inside stars themselves

• Two types• Pulsating (what

we’ll deal with today)

• Eruptive

Pulsating starsExpansion and contraction of surface

Pressure and gravity are not in equilibrium

Smooth change in light curve

Note: The smaller a single star is physically, the brighter

Extrinsic variables• Changes in brightness

are apparent• Two types

– Eclipsing binaries (what we’ll deal with today)

– Rotating stars• Eclipsing binary

– Changes in brightness caused from eclipses of two stars as they orbit each other

Primary eclipse happens when hottest star goes behind

Note: a higher mass star is smaller in size

MagnitudeMagnitude system - use certain stars as brightness

standards a higher magnitude is a fainter object

Apparent magnitude - measure of how bright a star appears at earth, regardless of distance

Absolute magnitude - apparent magnitude it would have if star were placed at distance of 10 parsecs

1 2 3 4 5

Bright Less Bright Dim Dimmer Dimmest

Lab Write Up• No percent errors • Still need 2 sources of error!

– “Skill” of mag. Meas.• Only rewrite data or calculations if neatness

is an issue• Graphs - label period, axes, connect points

– Make sure magnitude goes in correct direction!• Answer questions on pages 59&60

– Incorporate these into your conclusion section

Some physical considerations

• What are we trying to measure?– Magnitudes? Yes

• But! The physical cause of the variability is the MOST important thing we are trying to measure– What interferes with our ability to

determine the physical cause of the variability??

All Power Points are on my website:http://www.physics.unc.edu/~bpohl

Visit office hours or email me if you have questions! bpohl@physics.unc.edu

Morehead room 403

Monday (week-after-lab) 3:00pm-5:00pmTuesday (week-after-lab) 5:00pm – 7:00pm

Evaluations

• Please turn in evaluations to Craig• You are evaluating the planetarium portion of the

lab. Night labs evaluated separately • Comments are appreciated, Please be constructive

– Something I did well– Something that needs improvement