Handouts:
Syllabus
Course schedule
Todays Quiz
Topics:
Course Introduction
A tour through the Universe
The sky - Introduction
Scientific notation
Course Introduction:
Syllabus
Schedule
Homework with CAPA
Textbook: Voyages Through the Universe, by Fraknoi,
Morrison, Wolff
Textbook Website: http://www.harcourtcollege.com/astro/fraknoi/
Recommended: Redshift College Edition from Maris
Multimedia
A tour through the Universe
Objects in the Universe: Stars, Planets, Moons,
Nebulae, Galaxies, Galaxy Cluster
Galaxies contain lots of stars: ~200 Billion in ours
Stars generate their own light; Planets and Moons
reflect starlight
The solar system: 9 Planets (including earth)
orbiting around the Sun (a star)
and around themselves.
(Redshift Demo)
Sizes of objects in solar system vary a lot ! (see
figure P.7 in book)
Diameter: Earth: 13000km, Pluto: roughly half, Jupiter X11, Sun X110
Rotation roughly within one plane - except for
Pluto
(Redshift Demo)
A short break: Distances in Astronomy
The Universe is so big that one needs several length scales to describe it.
Average distance from Earth to Sun: 150,000,000 km
(=1 astronomical unit AU)
Size of the solar system (planets only): ~80AU (Pluto is ~40AU
away from sun)
Distance to the nearest star (not counting the
sun): Proxima Centauri: 269,000 AU
1 light year (1ly) = distance light travels in 1
year
Speed of light: 300,000 km/s -
so 1ly = 9,500,000,000,000 (9.5e12 km)
light travels
around the world in 0.1s
to the moon in 1.3s
to the sun in 8 min
to Proxima Centauri in 4.3 years.
Proxima Centauri is therefore 4.3 ly away.
Continue Tour of the Universe:
Other things than stars in our Galaxy. Example:
See image of Eagle nebula taken from Hubble
Space Telescope
A cloud of hydrogen gas and dust that forms into stars.
Size of our galaxy: 100,000 ly
Distance to next galaxy (Andromeda) ~2,200,000 ly
Size of the Universe: 14,000,000,000 ly (14 billion
light years)
more about this later in the term
There are some 100 billion galaxies in the universe
See Hubble Deep Field image - example how new
observatories changed view of cosmos
Because of finite speed of light looking at far
away objects is like looking back in time
(if Proxima Centauri explodes we will see this 4.3 y.
In other words: we see Proxima Centauri
as it looked 4.3 years ago)
Observing the sky - Introduction
Most things we know about the universe we know from
observing the sky. Only the moon
and most of the planets (except Pluto) have been "visited" by
spacecraft.
We can see around 6000 stars by the unaided eye
Night sky tonight: Constellations. In early days
mystic component - today we use the
names of constellations to mark zones on the sky for orientation.
(Redshift Demo)
Example Orion and Betelgeuze. (Redshift
Demo)
We will hear more about Betelgeuze - size 3AU !
Stars move during the night because of earths
rotation (but the relative distances
constellations remain the same) (Redshift Demo)
The earth takes 23h and 56min to rotate once. Then
stars at the same position
(Redshift Demo). (It will be
explained later why it is not exactly 24 hours)
But: some objects still move because they are so close that their motion
is noticable:
Greeks called them Planets (=wanderers). Today we
exclude Sun and Moons and call the heavy bodies orbiting the sun
"planets"
Which planet can we see tonight ? Why ?
Scientific Notation
A common notation for numbers that avoids huge
numbers of digits for very
small or very large numbers is called scientific notation
Examples:
100 = 1x102
1000 = 1x103
0.01 = 1/100 = 1x10-2
250,000,000,000 m = 2.5x1011
m
1ly = 9,500,000,000,000,000 m = 9.5x1015 m
Computers use E instead of x10.
Example:132 = 1.32x102 is
written as 1.32E+2
Significant figures
Many numbers are only known to a certain precision.
Example: If I measure the temperature with a
thermometer, but have only a quick look
I can say that it is 70F. It could be anything between 65 and 74F so 70
has only
one significant figure.If I look more careful I might find 72F, which
has 2 significant
figures and is more precise (between 71.5 and 72.4 - I cant tell for
example because
of the scale on the thermometer). To do a better measurement and to get
to know
more (significant) figures I need a better Thermometer (a digital
thermometer might yield
71.9 F - 3 significant figures).
If the temperature would be exactly 70 (between 79.5 and 70.4) one writes 70.
Rules: trailing zeroes with decimal point count as
significant figures
trailing zeroes
without decimal point do not count as significant figures
in scientific
notation, all figures before the x10 are significant
Examples
100 - 1sf
100. - 3sf
100.000 - 6sf
234 - 3sf
0.002 - 1sf
1.20x1022 - 3sf (the scientific notation part does not
count)