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 RevolutionEarth is not at the center of the Universe.

Nikolaus Copernicus(1473-1543)

100,000 light years

speed of light = 180,000 miles/second

~300 billion stars

QuestionThere are roughly 100 billion (=1x1011) galaxies in theobservable Universe. If there are about 300 billion (=3x1011)stars in every galaxy, how many stars are there in the observable Universe?

Answer: 3x1022 stars = 30 billion trillion

What if each star has one Earth-like planet?

4x1011

3x1022

3x1011

infinite

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 candeduce from looking at the stars in this image?

Hertzsprung-Russell (HR) Diagram

LuminosityColor (type)MassSizeLifetime

QuestionIf 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 mustcome to an end…

Planetary Nebula

~1 light year

QuestionIf this were the wholepicture, would we be here today? Why?

High Mass (OBA) Stars

QuestionIf this were the wholepicture, would we be here today? Why?

Note: Nitrogen is a product of Helium fusion.

Supernova

The energy releasedduring a supernovais equal to the entireenergy that the Sunwill release in itsentire life!

Planet Formation

Jupiter’s Orbit

dust

10-6 m

boulder

1 m

asteroid

104 m

planetesimal

106 m

AU = averageEarth-Sun separation

Star-Planet Distance [AU]

Cir

cula

rity

Terrestrial Planet Formation

Giant Planet Formation

Beyond the frost line, planetesimalscan grow from rock and ice. This leads to the formation of “planetarycores”, which are rocky/icyplanetesimals around 10x asmassive as Earth. These cores areso massive that they accrete gas, forming gas giant planets.

QuestionsWhere 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

CO2

CO2

Water

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

Summary1 - 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 higherpitch (smaller wavelength)as the car approaches andat a lower pitch (longerwavelength) as it recedes.

The light waves are ata 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 theplanet-star separation?

Extrasolar Planets - Transit Technique

QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.

We learn the size, mass anddensity of the planet!

Extrasolar Planets - Direct Detection

120 AU

Mass of Neptune? Jupiter?

Orbit of Neptune

QuestionWhy are there so many close-in, Jupiter-mass planets?