Download Astronomy Basics

Astronomy190 - Topics in Astronomy
Astronomy and Astrobiology
Lecture 4 : Astronomy Basics
Ty Robinson
Questions of the Day
• What does it mean to say that we are
made of star stuff?
• What are Kepler’s three laws?
• What is spectroscopy and how does it
help us to learn about the Universe?
Copernican Revolution
Earth is not at the center of the Universe.
Nikolaus Copernicus
(1473-1543)
100,000 light years
~300 billion stars
speed of light = 180,000 miles/second
Question
There are roughly 100 billion (=1x1011) galaxies in the
observable Universe. If there are about 300 billion (=3x1011)
stars in every galaxy, how many stars are there in the
observable Universe?
4x1011
3x1022
3x1011
infinite
Answer: 3x1022 stars = 30 billion trillion
What if each star has one Earth-like planet?
Composition of the Interstellar Material
Orion Nebula
~3 light years
~3,000 stars
10-2 light years
Star Cluster
~2 light years
Question
The stars in this cluster are all at the same distance from
Earth. What are two key features of stars that we can
deduce from looking at the stars in this image?
Hertzsprung-Russell (HR) Diagram
Luminosity
Color (type)
Mass
Size
Lifetime
Question
If it takes about 1 billion (=109) years for simple
life to originate and flourish on a planet, what
types of stars (OBAFGKM) are good places to
search for life?
all stars
OBA
G
FGKM
Low Mass (FGKM) Stars
E=mc2
All good things must
come to an end…
Planetary Nebula
~1 light year
Question
If this were the whole
picture, would we be
here today? Why?
High Mass (OBA) Stars
Question
If this were the whole
picture, would we be
here today? Why?
Note: Nitrogen is a product of
Helium fusion.
Supernova
The energy released
during a supernova
is equal to the entire
energy that the Sun
will release in its
entire life!
Planet Formation
AU = average
Earth-Sun
separation
dust
10-6 m
Jupiter’s Orbit
boulder
1m
asteroid
planetesimal
104 m
106 m
Circularity
Terrestrial Planet Formation
Star-Planet Distance [AU]
Giant Planet Formation
Beyond the frost line, planetesimals
can grow from rock and ice. This
leads to the formation of “planetary
cores”, which are rocky/icy
planetesimals around 10x as
massive as Earth. These cores are
so massive that they accrete gas,
forming gas giant planets.
Questions
Where is the frost line in our Solar System? Between
Earth and Mars? Between Neptune and Pluto?
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
Is frost line around an M-dwarf at the same distance
as the frost line around the Sun?
Kepler’s Laws
1 - Bodies orbit their parent star on elliptical orbits with the
star at one focus of the orbit.
2 - In an orbit, the closer a body is to
its parent star the faster it moves.
Kepler’s Laws
3 - The orbital period (P) of a body is related to the body’s
average distance from its parent star (a) by the equation
P2 = a3 (with P measured in years and a in AU).
Bottom Line: Close-in planets have shorter orbital periods!
Electromagnetic Spectrum
Emission and Absorption Spectra
• Whether the spectrum is continuous, or in emission or
absorption tells us about the composition and
temperature structure of the object we are studying.
CO2
Water
CO2
CO2
Questions of the Day
• What does it mean to say that we are
made of star stuff?
• What are Kepler’s three laws?
• What is spectroscopy and how does it
help us to learn about the Universe?
Quiz
1 - Explain two reasons why we limit our search for
habitable planets to worlds around low-mass, main
sequence stars.
2 - What three characteristics must a world have in
order to be considered habitable?
3 - What is one thing you did not understand from
today’s lecture?
A Multitude of Worlds
• 353 Planets
• 298 Planetary
Systems
• 38 Multiple Planet
Systems
Over 92% of the planets
discovered to date were
found using the Radial
Velocity (Doppler)
technique.
As of 7/21/09
Summary
1 - The Universe is a huge place and contains billions of
trillions of stars (at least!).
2 - The life cycles of high-mass and low-mass stars are
necessary for the production and distribution of the
chemical elements of which life is made.
3 - Kepler’s Three Laws
- orbits are ellipses
- closer = faster
- P2 = a3
4 - Extrasolar planets are detected by
- radial velocity (indirect)
- transit (indirect)
- imaging (direct)
Extrasolar Planets - Doppler Technique
The sound is at a higher
pitch (smaller wavelength)
as the car approaches and
at a lower pitch (longer
wavelength) as it recedes.
The light waves are at
a longer wavelength
(redder) as the star
moves away from you
and at a shorter
wavelength (bluer) as
the star approaches you.
Extrasolar Planets - Doppler Technique
Question
How can we determine the
planet-star separation?
Extrasolar Planets - Transit Technique
QuickTime™ and a
Sorenson Video 3 decompressor
are needed to see this picture.
We learn the size, mass and
density of the planet!
Extrasolar Planets - Direct Detection
Orbit of Neptune
120 AU
Mass of Neptune? Jupiter?
Question
Why are there so many close-in, Jupiter-mass planets?