How to “enroll” in this course
• Go to “bb” if from the campus network berkeley.edu,
otherwise “blackboard.berkeley.edu”
• Click “Create Account”. You will have to choose a username.
• Fill out all red-starred information slots, then “create account”
at the bottom
• Click “Course Catalog”; “Letters & Science”; “Astronomy”
• Click “Astro 10 (astron10-spr02)”
• You will have to use the username & password you chose
above to log in; this will be your username for the course
• Choose “Enroll in this Course” and follow directions
• You should end up in the Astro 10 Announcement screen
The CourseInfo website by Blackboard
The Website Discussion Forum
The Course
Syllabus
and
Plan
Grading and Exams
Further Comments
• There will be NO sections this week
• You are not in the course unless a GSI has enrolled you on the
course website into a section (Telebears aside)
• For that to happen, you MUST get an account in Blackboard
• Sections next week are all in the basement of Campbell Hall
• This is not a mathematical course, but there is simple algebra in
it (like L=R2 T4 ) a bit. Critical thinking IS required.
• The main source of material is the book, but lectures tell you
what is important (and fill out detail – the book is brief)
• Falling behind in reading or homework is fatal – this material
CANNOT be crammed at the end
• If you aren’t used to critical thinking, or don’t need the grade,
we strongly encourage you to take the course P/NP
Science vs Non-science (nonsense?)
• What is “science”?
– Empirical : must always be based on observations
– Predictive : should be able to predict new obs.
– Reductionist(?) : tries to discover underlying “laws”
• Why don’t astronomers believe in astrology?
– Precession has moved the “Sun signs”
– The constellations are not real entities
– Local forces are much greater than forces due to stars or
planets
– Astrology is not really predictive (rigorous statistical
analyses shows this)
[of course, just because it is not science doesn’t mean it should
be banned, just that it shouldn’t pretend to be science]
The Solar System
Our place in the Universe
Powers of Ten
We jump by a factor of 100
in each frame. This also
shows the context of the
Earth in the Universe.
Exponentials
We will use scientific notation extensively - namely exponentials.
The exponent indicates the number of places to the left (positive
exponent) or right (negative exponent), of the units place the decimal
point occurs. Another way to look at it is that the exponent for a power
of ten indicates how many zeros would come before a 1 if you wrote the
number out. Thus 10^6 (one million) is written as 1,000,000 (or 6
zeros). A negative power of ten means you divide by that number, eg.
10^(-6) is one millionth. If you multiply two powers of ten together,
you add the exponents. If you divide them, you subtract the exponents,
eg. 10^6/10^2=10^(6-2)=10^4.
Another concept that is useful is the precisionof a calculation. If you
m
ultiply several num
bers together, the answer shouldn't have m
ore
thanone m
ore decim
al place thanthe num
ber beingusedthat hadthe
LEASTnum
ber of places (or precision). For exam
ple, 1.2x10^4tim
es
3.563x10^2is 4.3x10^6, not (as m
y calculator says) 4.2756x10^6. In
any case, inthis class we are alm
ost never interestedinnum
bers to
better than2decim
al places (astronom
y is a rather approxim
ate
science, for the m
ost part).
The Universe in a Day
Let’s look at the entire history of the Universe as though it took
place in a single day. The present is at the stroke of midnight at
the end of that day. Since it is about 12 billion years old, each
hour will be worth 0.5 billion years. A million years takes only
a little over 7 seconds.
The Big Bang (as an opaque fireball) and the formation of H
and He all take place in the first nanosecond. The Universe
becomes transparent in about 2 seconds. The first stars and
galaxies appear after about 2am, and our Galaxy forms at
perhaps 4am. Generations of stars are born and die.
Timeline graphic
The Universe in a Day
The Solar System does not form until 3pm. The first life (bacterial)
appears on the Earth by 4pm. Our atmosphere begins to have free
oxygen at 7 or 8 pm, and this promotes the development of creatures
which can move more aggressively and eat each other. Life does not
begin to take on complex forms (multicellular) until 10:45pm. It moves
onto land at 11:10. The dinosaurs appear at about 11:40, and become
extinct at 11:52. Pre-human primates appear at around 14 seconds
before midnight, and all of recorded history occurs in the last 70
milliseconds.
Looking to the future, we can expect the Universe of stars to go on for
another at least a millennium (using the same time compression factor).
After that, there are other ages of the Universe (not dominated by
stars), which grow colder and more bizarre, and take place on
astronomical timescales (even after this compression of timescale).
A Scale Model of the Solar System (1)
• Let’s make everything one-billionth (10-9) as big as it
really is (9 orders of magnitude smaller)
• The Earth: Diameter = 13000 km = 1.3x107 m
1.3x107x10-9 ~ 10-2 = 1.3 cm (a marble)
• The Sun: Diameter = 1,400,000 km = 1.4x109 m
(about 100 times the Earth’s)
so it must be 1.4 m (about a foot less than my height)
• Earth-Sun Distance = 1.5x1011 m
(1 Astronomical Unit)
1.5x1011x10-9 = 1.5x102 m = 150 m
or about one-and-a-half football fields
A Scale Model of the Solar System (2)
•Jupiter Distance = 5 AU,
•Saturn Distance = 10 AU (downtown Berkeley)
•Pluto Distance = 35 AU (6 km: Oakland)
•1 Light Year: 3x108 m/s x 3x107 s/yr ~ 1016 m or 1013 km
scaled down, that would be 1013-9 km or 10,000 km
(about the distance to Europe)
•The nearest star is 4 light years away....
•The center of our Galaxy is 25000 ly away!!
(scaled down, back out beyond the Sun...)