astronomy 105 laboratory lab 11 - sfa physics, engineering ...celestial equator ecliptic sun’s...
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LAB 11
Astronomy 105 Laboratory
AST 105Review for Lab Exam
Ast 105 Lab ExamWeek of April 16, at normal lab time.
Don’t be late!!
Items to bring…- One scantron (882-E)
- two pencils
Study!
About 3-5 questions from each lab exercise
Review
Main concepts covered
Procedures and measurements
Questions and calculations
Bring a scantron: 882-E
Review material – Power point slides online
CONSTELLATIONS – SKY
FAMILIARIZATION
North
South
Celestial Equator
Ecliptic Sun’s Path
Eas
t
Summer
Solstice
Vernal
Equinox
Autumnal
Equinox
North
South
East
March 7 @ 8:00 p.m
Meridian
Zenith
32° X
West Horizon
March 7 @ 8:00 p.m
Meridian
not visible
WestEast
East HorizonWest Horizon
Sky Familiarization
A Few More Things to Remember
Any vertical line on your SC-1 (north-south) is a
meridian.
Approximately one half of the stars on the SC-1
are visible at any given time (12 hours of RA).
Meridian moves eastward 4 minutes each day
(Earth’s revolution)
Meridian moves eastward 1 hour of RA for every
hour of time (Earth’s rotation)
SCIENTIFIC
MEASUREMENTS
Scientific Experiments / Observations
Physical quantities can never be
measured with absolute precision
How Many Significant Figures
0.089 2
1.089 4
12000 2
12001 5
Scientific Notation
3.502 x 106
decimal number (1-9)10 raised to an
integer power
Number Significant Figures Scientific Notation
9004 4 9.004 x 103
0.000007 1 7 x 10-6
43 2 4.3 x 101
7,805,000,000 4 7.805 x 109
0.0408 3 4.08 x 10-2
8.4 2 8.4 x 100
To multiply two numbers in scientific notation multiply the
decimal parts of the numbers and add the exponents
algebraically.
(4.0 x 104)(2.0 x 103) =
(4.0 x 2.0)(104 x 103) =
(8.0) x (104+3) =
8.0 x 107
(6.0 x 102)(2.0 x 105) = 12.0 x 107 = 1.2 x 108
Units
Provides numerical context for a measurement
Unit conversion
Ex. Convert 500 kilometers into centimeters
1000 m = 1 km 1 m = 100 cm
500 𝑘𝑚 ×1000 𝑚
1 𝑘𝑚×100 𝑐𝑚
1 𝑚= 5 × 107cm
1000 𝑚
1 𝑘𝑚= 1 and
100 𝑐𝑚
1 𝑚= 1
THE MOON
N.P.N.P. N.P.
N.P.
N.P.
Synchronous
Rotation
Does the Moon rotate on it’s axis?
What is the Moon’s hidden side?
N.P. Noon
Sunset
Midnight
Sunrise
N.P. Noon
Sunset
Midnight
Sunrise
N.P. Phase: 1st quarter
Rise Time:
Set Time:
Transit:
Noon
Midnight
Sunset
MERCURY’S ORBIT
10 20 30 40 50 60 70 80 90 100010 km
6
SUN
Name (print):__________________________________ Section: _____
0.70.60.50.40.30.20.10.0AU
0.8
110 120
Mercury’s Orbit
Major Axis
Equal Time Intervals
F F
Verifying Kepler’s 1st
Mercury’s Orbit
Major Axis
10 20 30 40 50 60 70 80 90 100010 km
6
SUN
0.70.60.50.40.30.20.10.0AU
0.8
110 120
Verifying Kepler’s 2nd
Equal area in equal time.
Mm
a
G
4πP
322
2
324
P
a
GMm sunm
sunsunm MMm
Kepler’s 3rd
)(
4 2
MmGk
2
324
P
a
GM sun
Finding the Sun’s mass.
P2=ka3
EMISSION SPECTRA
Formation of Emission and Dark Line Spectra
THE EARTH’S ORBITAL VELOCITY
1
2
3
4
5
Velocity = 0
Increasing
Velocity
Increasing
Velocity
The Doppler Effect
o
r
cv
Arcturus
VA
VB
? ?
0A
λ
Δλcv
o
From measured
Doppler Shift
1.Orbital velocity of Earth
2.Radial velocity of Arcturus
3.Radius of the Earth’s Orbit
THE HR DIAGRAM
Apparent Brightness of Stars
Stellar Luminosity -- Total amount of light
energy emitted each second
Surface Area
Temperature
Distance from the Earth
Magnitude
Stellar Brightness
Apparent Magnitude (mv) - Brightness from Earth
Absolute Magnitude (Mv) - Brightness from 10 pc
Absolute magnitude depends only on a star’s luminosity (the star’s wattage)
Magnitude Difference
Brightness Ratio (Brightness Difference)
1 (2.512)1
2.5 2 (2.512)
2 6.3
3 (2.512)3 15.9
4 (2.512)4 40
5 (2.512)5 100
6 (2.512)6 251
Spectral Classification
B
The Sun
M=+5 G2
O B A F G K M
-10
-5
0
+5
+10
+15Ab
so
lute
Mag
nit
ud
e
Temperature
HR Diagram
Luminosity Class
Size
Ia & Ib Supergiant
II Bright Giant
III Giant
IV Sub-giant
V Dwarf
The Sun’s Spectral and Luminosity Class: G2 V
Star mv Mv
Spectral
Type
Luminosity
Class
Aldebaran +0.9 -0.2 K5 III
Alpha Centauri A 0.0 +4.4 G2 V
Antares +0.9 -4.5 M1 I
Canopus -0.7 -3.1 F0 II
Fomalhaut +1.2 +2.0 A3 V
Regulus +1.4 -0.6 B7 V
Sirius -1.4 +1.4 A1 V
Spica +0.9 -3.6 B1 V
Which star appears faintest in our sky? Regulus
Which star has the greatest luminosity?
Which star has the highest surface temperature?
Which star is a red giant?
Which main-sequence star has the longest lifetime?
Antares
Spica
Aldebaran
Alpha Centauri
STELLAR PARALLAX
1 AU
Sun
Earth
Star 1 Star 2 Star 3
1 arcsec
1/2 arcsec
arcsec
1/3 arcsec arcsec
1 pc 2 pc 3 pc
1 parsec 2 parsec 3 parsec
A star with a parallax of 1 arcsecond is at a distance of 1 parsec (1 pc = 3.26 ly)
5 light-years 10 light-years
More distant stars have smaller parallaxes.
=1
A star’s distance in parsecs is given by
where d is in parsecs and p is in arcseconds
Stellar Parallax
• Motion of Earth cause parallax shifts
• Used to find distance to stars out to a few hundred light-years
• Parallax is ½ of measured shift
• More distant stars have a smaller parallax… a star with ½ the parallax
of another star is 2x farther away
• d = 1 / p “p” is in arc seconds and “d” is in parsecs
THE PLEIADES
Stars in a Cluster•Common Properties
•Distance
•Age
•Different Properties
•Spectral Types (temperature)
• Luminosity Class (size)
d >10 pc
10 pc
d <10 pc
10 pc
Star Cluster
d >10 pc
d <10 pc
O B A F G K M
-0.4 color index 1.3
Main-sequence
HR Diagram
-0.4 color index 1.3
Color-Magnitude
Diagram
Distance Modulus = m - M
The difference between the absolute magnitude and
the apparent magnitude can be used to find the
distance to a star cluster.
If m-M > 0 then the distance to the cluster is > 10 pc.
If m-M = 0 then the distance to the cluster is = 10 pc.
If m-M < 0 then the distance to the cluster is < 10 pc.
DM{
Cluster A: Distance 50 ly
Cluster B: Distance ?
The apparent brightness of the
stars in Cluster B are 4 times
fainter than the stars in Cluster A.
What is the distance to Cluster B?
Inverse-Square Law: √4 = 2
Cluster B is 2 times farther or 100 ly.
AGES AND DISTANCES TO CLUSTERS
Interstellar Dust Reddens Light (makes stars appear cooler)
Dims Light (makes stars appear further away)
age of cluster = lifetime of stars
at main-sequence turnoff point
B6 stars -- 60 million yrs.
MS lifetime
Pleiades - Open Cluster
Distance - 380 ly Age - 60 million years
HUBBLE’S LAB
V = 0 2800210014007007001400
km/sec
10 Mpc 20 Mpc 30 Mpc 40 MpcMilky Way A B C
V = 02800 2100 14007007001400
km/sec
10 Mpc 20 Mpc30 Mpc40 Mpc
Milky Way A B C
10 Mpc20 Mpc Alien’s Galaxy
Recessional Velocity is Proportional to Distance
The Universe is Expanding!!
v = Ho dHubble Diagram
Finding a Galaxy’s Distance Hubble’s Law
d = v / Ho
To Find Distance:
Measure recessional velocity (red shift)
132 Mpc
Sample Galaxies
Distance
images
Recessional Velocity
spectra
v = Ho x dHubble Diagram
Hubble Diagram
Procedure
- plot data
- draw best fit line
- find slope (Ho)x
x
x
x
x
rise
runslope = rise/run
ROTATION OF SATURN
Earth Distant Star
Laboratory - No Radial motion
Radial Velocity = 0
Radial Velocity -
Radial Velocity +
Laboratory Spectrum
Blueshift
Redshift
Spectral Lines Match
o
Earth Distant Star
Laboratory - No Radial motion
Radial Velocity = 0
Radial Velocity -
Radial Velocity +
Laboratory Spectrum
Blueshift
Redshift
Spectral Lines Match
o
o
rλ
cΔλv
Radial Velocity -
Radial Velocity +
The Doppler Effect: Measuring the Radial Velocity of a Star
Important: Do not write or mark on theSaturn Handout
Spectroscope Slit
No Doppler Shift from
this Light
Light from here
shows the largest
Blue Shift
Light from here
shows the largest
Red Shift
A
BSaturn
c
VλΔλ 0B 2
o A
B
sec
km
04λ
ΔλcV
V
V
0λ
ΔλcV Doppler
c
VλΔλ 0A 2
o
sec
km
04λ
ΔλcV
Top
Bottom
(mm) = Top Distance – Bottom Distance
Reference
Line
c = 300,000 km/s
o = 6200 Å
Finding the Rotation Period of Saturn
Saturn
V Period = Distance / Velocity
Distance = Equatorial Circumference = 2RR
P = 2 R / V
V
R2P
Period (P) – Rotation Period
THE END