Download Lecture 02a: Setting a context for us in the Universe

The Solar System, stars, the Universe…
…and you
Setting a context for us in the Universe
The solar system;
• Other stars;
• Our Milky Way Galaxy;
• Other galaxies;
• The Big Bang;
• The enormity of timelines;
•
Take home message: a good idea of our place in space, and how the
building blocks of life came to be.
Scientific notation
Before we can even begin…
10,000 = 1×104
600,000 = 6×105
0.00008 = 8×10-5
The Solar System
All the objects within the Sun’s zone of gravitational influence.
The Sun
–
99% of the solar system mass;
–
110 × Earth’s diameter;
–
4.5 billion years old (10 billion year life expectancy);
–
An unremarkable star.
Tiny Terrestrial Planets
Mercury – hot, airless;
Venus – hot, thick atmosphere;
Earth – moderate atmosphere, warm.
Moon – no atmosphere, chillier.
Mars – tiny atmosphere, chilly indeed.
Giant Jovian Planets
Jupiter – enormous, about 1% stellar mass.
Saturn – very large, spectacular rings.
Uranus – cold, relatively quiet; tilted sideways.
Neptune – strangely turbulent.
Solar System Detritus
Interplanetary dust
Asteroids
—Asteroid
belt (2.1-3.3 au);
—1-2×106 objects; 4% Moon’s mass.
Kuiper belt
—30-50
au;
—105 cometary objects;
—Largest known is Eris (2500 km diameter).
Comets
—Periodic
(i.e., Tempel, 5.5y orbit);
—Öort cloud (50,000 au);
—1012 cometary objects.
The Solar System:
distance scale
(set 1 au=15m, 50 ft)
Sun: diameter=17 cm (6.6 inches)
Earth: diameter = 2 mm (1/16 inches);
15 m from Sun
Jupiter: diameter = 1.4 cm (1/2 inch);
80 m from Sun
The Sun and
Jupiter
The Solar System: distance scale
(set 1 au=15m, 50 ft)
Neptune: diameter = 0.5 cm (1/5 inch);
450 m from Sun (1/4 mile)
Kuiper belt: 450-750 m from Sun (1/4 – 1/2 miles)
Sun, Neptune,
Kuiper Belt
The Solar System: distance scale
(set 1 au=15m, 50 ft)
Öort cloud = 750 km (470 miles)
(Sierra College to San Diego)
Nearest star = 4000 km (2500 miles)
(Sierra College to New York City)
Stars
Our Sun is a relatively
common type
Stars
Each different kind has a different life history…
The bigger stars have more raw fuel…
…but, they use it faster
 Big stars burn out quickly
 Big stars produce a great deal of harmful radiation
The smallest stars have very little raw fuel…
…but, they use it sparingly
 Tiny stars live very, very long times
 Tiny stars produce low energy radiation
Stars and nucleosynthesis
Stars turn hydrogen into helium via nuclear fusion;
Stars also fuse helium into carbon, and the most massive engage in
even more complicated atomic fusion reactions that produce other
atoms such as phosphorus, nitrogen, etc.
Carbon stars are giants that lose up to half their mass via huge winds
that blow off their surfaces.
Supernovae: friends and foes
Produce atoms more massive than iron.
Cause ionizing events – there is no defense!
The Milky Way Galaxy
A massive grouping of stars, dust, and gas, and related
phenomena.
Dimensions
Disk 100,000 LY across; 1000 LY thick;
– We are 28,000 LY from center;
– 100 billion times mass of Sun (interior to Rsun).
–
Galactic recycling (star-gas-star cycle)
Interstellar medium (ISM) is mostly H, He;
Star formation occurs;
Stars produce winds which churn and fertilize the ISM;
Stars supernovae, further fertilizing the ISM.
Types of galaxies
1.
Spirals
2.
Ellipticals
3.
Irregulars
4.
Active
All galaxies seem likely to harbor supermassive black holes
(108 × the mass of the Sun).
These black holes were apparently more active in the distant
past.
Galactic evolution
Central black holes calm down in time;
Galaxies collide with each other;
Galaxies consume their interstellar matter;
Important: not all galaxies have as much dust and gas as ours does!
Galaxy groups
Galaxies occur in clusters
Clusters occur in superclusters
–
Nearest large galaxy (Andromeda galaxy) is
2.5 MLY away.
–
Superclusters are about 100 MLY across.
Receding galaxies
Redshift studies have revealed that nearly all galaxies are rushing
away from us.
The farther a galaxy is from us, the faster it is rushing away.
Truly distant galaxies are rushing away from us at speeds
approaching the speed of light!
What is the matter with us?
The Big Bang
Galaxies are receding from us because space is expanding.
This is NOT a cosmic explosion in space. It is a cosmic explosion
OF space.
All points in the Universe see galaxies receding from them.
This was the first hint of the Universe’s history, treated by the Big
Bang Theory!
Consequences of the Big Bang theory
The Universe…
… enlarged and cooled with time
… started out as pure H and He.
… continues to age…
The Big Bang theory accurately explains the relative H and He
concentrations in the Universe, its clumpiness, age, background radiation,
and other things.
Dark Matter and Dark Energy are recent discoveries needed to explain
some observations.
… See Astro 5, Astro 10, or (especially) Astro 25 for details!
The Enormity of Timelines
Age of Universe:
13.5-14 billion years
Age of Milky Way Galaxy:
at least 13.2 billion years
Age of Sun:
4.6 billion years
Age of Earth:
4.5 billion years
First life on Earth:
3.7 billion years
Homo sapiens
200,000 years (0.0014% of Universe’s age)