Chapter 15
• Measuring star properties - Section 15.1
– Range of values for stars
– Typical values for stars
• Sections 15.2 and 15.3 =
HR diagram and what astronomers
learned from studying it.
Goals & Outcomes
• Learn some simple astronomical terminology.
• Develop a sense of what scientists know about the
overall universe, its constituents, and our location
• Understand the data that led to the development of
modern cosmology and the Big Bang theory
• Explain how electromagnetic radiation and
astronomical instruments are used to reveal the
properties of stars and galaxies.
• Diagram the process of nuclear fusion.
• Describe major star characteristics
• Contrast the life history of a low-mass star with the
life history of a high-mass star.
Write a list of properties astronomers
might want to measure or know
• ___________________
– _____________
– ______________
•
•
•
•
•
___________________
___________________
_________
____________________
_____(we’ll discuss this one at the end of this
PowerPoint)
How Astronomers Measure _________
• Can be ________________________:
– Measure ______________and ____________
– We’ll discuss both of these again later
– Measure _________________________________
•
•
•
•
•
______________________________________
Easy or hard?
Measure/calculate ____________. Easy or hard?
Use __________________________________
See pages ___________________
_______________- continued
• HUGE range:
•
• Sun’s Luminosity =
• Typical
. ________are ____likely.
• Extremely luminous stars are ______________to find.
• Nearby, we find _________________faint stars
than luminous stars
– Why? What does this mean?
– (see page _______________________)
How Astronomers Measure _________
• Three techniques:
– _____________ (pages ______________)
– ____________(not in textbook because ____
__________________________________.
We’ll see why.)
– _________________(pages ____________)
Measuring _____using __________
• Example: Finger on outstretched arm
– Explain on chalkboard.
• Regular figure 15.3, page _________
• Interactive Figure 15.3
• See Lecture Tutorial, pages 35-42 to make your
own parallax calculations
• Shift is called _________________. Depends on:
– ________________________.
• Angle gets ________ as distance __________. [clicker ? next]
– ____________________________________(baseline)
• Angle gets ________ as separation __________. [2nd clicker ?]
Two identical objects, one closer, one
further. Which one shows a larger
parallactic shift?
1.
2.
3.
4.
Closer one
Further one
Both are the same
Not enough information
Which produces a larger parallactic
shift?
1.
2.
3.
4.
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Two telescopes close to each other
Two telescopes far apart
Both are the same
Not enough information
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Parallax - continued
• Can measure the distance to the _______
____stars this way, only ___________away.
• For those of you who like math:
– Parallax Angle in angle units of arcseconds =
(1 ÷ distance). Distance in units of “parsecs”
– 1 parsec = 206265 AU = 3.26 light years
• This number comes from the fact that there are
206265 arcseconds in one radian.
– Alpha Centauri is ____________ parsecs away.
• Every other star is _________________.
Measuring _____using _____________
-- Technique not in your textbook -• How big something looks, called “_________” depends on:
–
–
–
–
_____________ (how many ________________________)
______________________________
Math: _____________________________.
Know any 2 of these 3 numbers, calculate the 3rd.
• What we see for stars:
– Sun’s radius is only 700,000 km (_________ miles, ____Earths)
– Closest stars are ____________light years away
– _______________= 0.005 arcseconds, 40 times __________
__________________________________________________
– Only can measure angular size using radio interferometry
• Galaxies are big enough to see as more than dots.
– Can use this technique.
Measuring ________using __________________
• How bright something looks, called “_____________”
depends on:
– ___________________________
• Objects with a known ____________are called “standard candles”
• Examples include: Type 2 _____________________(page 590),
________variable stars (pages 535, 640-644), and entire galaxies.
–
–
–
–
____________________________
Math: Brightness = Luminosity / [4 p (distance)2] See p. 520
Know any 2 of these 3 numbers, calculate the 3rd.
See also pages 640-644
• ________this relationship ___________________after
_________________________________.
Measuring ________________
• Measured several ways
– ______________star (pages 524-525)
• Often take pictures using 2+ filters to measure ____
• _________________________. _____absorbs blue
light more than red light.
– ____________________________(chapter 5)
– Best method: ___________________________
Measuring _______________
using ___________________
• Relationship is not obvious, struggled.
– Originally, strong lines = “A” class star,
few/weak lines = “O” class star.
– System didn’t work.
– _________________________________________ figured it out.
• Annie Jump Cannon, Williamina Fleming, Antonio Maury, and finally Cecilia
Payne-Gaposchkin.
• Cannon removed duplicate classes, re-ordered from hot to cold.
• She was awesome. Read about her in your textbook!
• __________________________________________
• __________________________________________________
– Two new classes of cold brown dwarfs (almost stars): LT (see
footnote on page 525)
• Temperature range: __ stars = _____________. __ stars = _____
• Sun is a ________________. Typical stars are ___________.
Measuring star masses
• Can measure directly ___________________________
– _______________________________. See page 527.
– Measure 2 of these 3: __________________________
• How measure __________? __________? [___________is tough.]
• What would be easiest to see orbiting a star?
– __________________________!
– ______________star. See pages 527-529 for details.
– __________________of stars in sky are ________systems
• Interactive Figure 15.8, Additional: Spec. Bin. Movie
• Mass range:
. Typical
– Less than
and object stops shrinking before core
heats up to turn on fusion. “______________” or “failed star”
– Bigger than
and own solar wind evaporates star.
Measuring Star Composition
• How do we measure composition?
• Range: ____. Stars are ______________.
1. ________________________
2. ______________________
3. _____________________
•
Very first stars were made of…
–
•
Next generation have …
–
•
“___________________”
“_____________________________”
Current generation have …
–
“__________________________”
Summarizing Star Properties
• Luminosity range:
– Sun’s Luminosity =
– Typical
. ________are ____likely.
• Distances:
(if in ________)
• Temperature range: _ stars = _____________.
__ stars = _____________
– Sun is a _______. Typical stars are ___________.
• Mass range:
– Typical
• Sun’s Composition: ______________________
– ________________________________________.
Finding patterns
• Now we know how star properties are measured.
• We also know what we find, generally.
• Astronomers wanted to see if any other patterns
exist. Questions like:
– Are the hot stars always big? Small?
– How does mass relate to luminosity? Temperature?
Composition?
– Questions you have were probably the same as those
being asked 100 years ago.
– Hertzsprung and Russell first gathered data on
questions like these.
– They graphed the results in what’s now called the “HR
diagram.” You’ve already seen one in a Lecture Tutorial
exercise.
HR diagram
• HR = Hertzsprung-Russell
• Horizontal axis: _______________, listed in order of
the ___________________________
– ______________________________________
– Add ______________________________________
– What’s a ______________________________?
• Vertical axis: _______. Measured relative to ________
– Symbol for ____________________________
• Sun’s location on HR diag: _____________________
• With your neighbors, decide:
– Where are the hot stars? Cold stars
– Luminous? Faint
– Label the four corners with surface temperature & luminosity
(hot, cold, luminous, dim)
– Clicker questions coming.
Stars in the top right of the HR
diagram are:
1. Luminous
2. Faint
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Stars in the top right of the HR
diagram are:
1. Hot
2. Cold
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Another property shown on
HR diagrams
• On your HR diagram, figure out where the
biggest and smallest ___________ stars are.
– Clicker questions coming.
Which corner of the HR diagram
has the largest radius stars?
1.
2.
3.
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Top right
Bottom left
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Which corner of the HR diagram
has the smallest radius stars?
1.
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Top right
Bottom left
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Which color are M stars?
1. Red
2. Blue
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Which color are O stars?
1. Red
2. Blue
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Which star is larger? Both have the
same luminosity.
1. Hotter star
2. Colder star
3. Both the hot & cold star are same size
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What we see in nature
• You now understand what an HR diagram shows.
• Take a look at figure 15.10 on page 514.
• 3 regions on the HR diagram where stars are:
– Main Sequence
– Red Giants (and supergiants)
– White dwarfs
• What can we conclude from this observation:
_______________________________________
• We also now know:
– ___________________________________
– ________________________ (although they can be active)
• Novas, white dwarf supernovas.
• When we measure masses we get … but first …
– How do we measure masses?
– Masses on Main Sequence…
NAMES: “Dwarf” stars
• Lots of “dwarfs” in astronomy
– All _________________ are called ________
• __________ dwarfs & ___________ dwarfs
• TERRIBLE name. They’re ________________.
– _________________ dwarfs
• What color are they?
– ______________ dwarfs
• ____________________________________
• DO NOT MIX UP WITH ___________________.
– ___________________ dwarfs
• What are these?
Which kind of dwarf is biggest?
1.
2.
3.
4.
5.
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Black
Blue
Red
White
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Which type of Main Sequence stars are
easier to make (i.e. more numerous)?
1. Super-bright
2. Super-faint
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Based on figure 15.10, 15.11, 15.14,
which stars are more numerous
1. Hotter than Sun
2. Colder than Sun
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Ages of stars
• Why do stars die?
• To help us determine what causes this,
let’s use an analogy.
• A car “dies” when it _________________.
• What ______ primary factors determine
when it _________________________?
– _________________________________
– _________________________________
• Star equivalents to these?
Which kind of main sequence star has
a larger “gas tank”? [How much more?]
1.
2.
3.
4.
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Low mass
Same
Not enough information
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Which kind of main sequence star uses
its fuel faster? [How much more?]
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Low mass
Same
Not enough information
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Based on those two questions, which kind of
main sequence star lives longer?
1.
2.
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4.
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Same
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Are there many dead red dwarfs?
1. Yes
2. No
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Properties of stars
• High mass main sequence
• Low mass main sequence
Do stars lose a lot of their mass during
their main sequence lifetimes?
1. Yes
2. No
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Would you rather live life as a highmass star or low mass star?
1. High mass
2. Low mass
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Do stars evolve ALONG the main
sequence?
1. Yes
2. No
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REVIEW: What’s happening to the
number of gas particles in the center of
main sequence stars?
1. There are more (increasing)
2. There are less (decreasing)
3. Staying the same
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Which is more luminous?
1. M dwarf
2. M giant
3. Same
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Stellar evolution
• If we wanted to see how humans changed over
their lives, how could we do that?
• Studying stellar evolution requires either:
– ___________________. Can we? Why or why not?
– What else?
• _____________________________________________
• How can we do that?
Star Clusters
• To see stars in different stages, __________
_________________________________.
• Clusters = many stars born from same cloud
– All stars _______________________________
• ______________ difference = _________ difference.
– All stars _______________________________
– All stars _______________________________
• Differences in appearance would be because ….
Which cluster is older?
Decide now. Next slide = clicker.
Cluster A – pay attention to the blue
Cluster B – the Main Sequence
triangles. The band is the Main Sequence
band isn’t shown on this figure.
Which cluster is older?
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Cluster A
Cluster B
Same
Insufficient information
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The cluster I’ve drawn on the board
is:
1. Older than 10 billion years
2. Young
3. Between “young” and 10 billion yrs
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The cluster in figure 15.19 is:
1. Old
2. Young
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REVIEW QUESTIONS: Which has
a hotter surface?
1. M dwarf
2. M giant
3. Same
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Which has the hottest surface?
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2.
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B class main sequence
Red giant
Sun
M dwarf
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Which is smallest?
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2.
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Red giant
Sun
M dwarf
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Which has the coldest surface?
1.
2.
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Red giant
Sun
M dwarf
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Which is NOT fusing Hydrogen into
Helium in the core?
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2.
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B class main sequence
Red giant
Sun
M dwarf
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Which will have the longest life?
1. B class main sequence
2. Sun
3. M dwarf
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Which cluster is oldest?
1. Main sequence turnoff at high lumin.
2. Main sequence turnoff at low lumin.
3. Insufficient information to answer
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