Transcript Document

This Next Group of Slides
• This next set of slides deals with measurement,
Scientific Notation, QWIZDOM unit set-up,
lightyears and parsecs, the nature of science.
• Units covered are 3 and part of 4.
The Metric System
English Units (Distance)
12 divisions = 1 inch
12 inches = 1 foot
3 feet
= 1 yard
5.5 yards
= 1 rod
4 rods
= 1 chain
10 chains = 1 furlong
8 furlongs = 1 mile
3 miles
= 1 league
Metric Units
10 millimeters
= 1 centimeter
100 cm
= 1 meter
1000 m
= 1 kilometer
1000 milligrams = 1 gram
1000 g
= 1 kilogram
Scientific Notation
• 0.0000001 meters is difficult to
read and write; too many zeros.
• Use scientific notation to
simplify.
• 0.0000001 m = 110-7
Move the decimal place seven
places to the left to determine
the power/exponent of ten.
– Moving it to the left makes the
power negative.
– Moving it to the right makes the
power positive.
Commonly used prefixes
Number
Scientific
Notation
Prefix
Abbreviation
1,000,000,000
1  109
giga
G
1,000,000
1  106
mega
M
1,000
1  103
kilo
k
1  10-
centi
c
1  10-
milli
m
1  10-
micro

1  10-
nano
n
0.01
0.001
0.000001
0.000000001
2
3
6
9
Special Units
• The Light Year (ly)
– Distance light travels in 1
year. (1 Earth year.)
– Equivalent to a “look-back”
time; it’s how far back in
time we are seeing.
– Example: Proxima Centauri
is 4.1 ly away. The light we
see from it today left the
star 4.1 years ago. We see it
as it was 4.1 years ago.
• The Parsec (pc)
– “PARallax SECond”
– Distance to a body whose
parallax motion covers 1
second of arc.
– 1 pc = 3.26 ly
The Scientific Method
• The Scientific Method is the
procedure scientists use to
construct their ideas about how •
nature (everything) works. The
hope is to come up with a:
• Scientific Theory/Model/Law
– Concerns
observable/measurable things.
– Explains observable things.
– Must be testable.
– Must be disprovable.
– Predictive!
A Model is a description of
physical phenomena that
we feel matches well with
reality.
- The Celestial Sphere, sort of.
- Universal Gravitation
- Electron Orbitals
Principle of Uniformity
• The Laws of Science are the same everywhere in the
universe.
• The Laws of Science are the same everywhen in time
(starting at some time following the Big Bang).
If these aren’t so, then any model of the universe is
possible and, perhaps, equally valid.
This Next Set of Slides
• This part of the lecture covers, matter,
fundamental forces, beginnings of astronomy,
the path of the sun through the sky throughout
the year, the seasons, and precession.
• Units covered: 4 and 6.
The Nature of Matter
• Protons (positively charged) and neutrons (uncharged) make
up the nucleus at the center of an atom. Electrons (negatively
charged particles) are found relatively far from the nucleus.
– If the nucleus were the size of a grape, the closest electrons would
orbit at a distance about the length of a football field.
– Most “solid” matter, then, is made up of mostly empty space!
Fundamental Forces in Nature
• Gravitational Force
– Force between objects
with mass.
– Infinite in range, but
weakens with distance.
– Weakest of all forces.
• Electromagnetic Force
– Force between charged
bodies.
– Like charges repel…
– Infinite in range, but
weakens with distance.
• Strong Force
– Force that holds atomic
nuclei together
– Very short range – 10-15
meters!
• Weak Force
– Force responsible for
radioactive decay
– Very short range – 10-18
meters!
– (Really, related to
electromagnetic force.)
Elementary Particles
• Smaller particles
known as quarks,
make up protons
and neutrons.
– Up quarks
– Down quarks
The description of the universe and its
contents using elementary particles is
called The Standard Model.
• “Up” and “Down”
are just labels.
• Other kinds of
quarks have names
like “strange” and
“charm”, and again
are just labels.
WHY Astronomy (for ancient peoples)?
* A sense of wonder! The night sky is an amazing
and beautiful thing to look at and think about!
* Navigation
* Agriculture (when’s the rain coming?), Calendar
* Curiosity.
* Superstition. Guidance. Connection to gods.
* Time.
The Annual Motion of the Sun
• As the Earth revolves
around (orbits) the Sun, the
Sun appears to move
through 13 constellations
on a belt around the
celestial sphere called the
ecliptic.
• When the sun in the sky is
in “front” of a particular
constellation, we say that
the Sun is “in” that
constellation.
• As this motion repeats itself
after one year, it is called
the Sun’s annual motion.
The Ecliptic
•
•
•
•
The ecliptic ‘belt’ on
the celestial sphere is
tipped relative to the
celestial equator due to
the 23.5° inclination of
the Earth’s rotational
axis.
In June, the Sun
appears north of the
celestial equator.
In December, the Sun
appears south of the
celestial equator.
Twice a year, the sun
appears on the celestial
equator – these times
are called the
equinoxes.
The Seasons I
• The Earth’s
inclination is
ultimately
responsible for the
change in seasons.
– In June, the
Northern
Hemisphere is tilted • Common Myths:
towards the Sun.
– Summers are warmer because the Earth is closer to
the Sun than in Winter.
– In December, the
• Actually, the opposite is true in Northern Hemisphere!
Northern
– The tilt of the Earth’s axis brings the Northern
Hemisphere is tilted
Hemisphere closer to the Sun in Summer, and farther
away from the Sun.
from the Sun in Winter creating the seasons.
• Geometry is true, but this accounts for only a minute
fraction of the extra heating in summer.
The Seasons II
• This tilt of the Earth has
two important effects:
– In Summer, the Sun
spends more time
above the horizon –
days are longer,
resulting in more
heating.
– In Summer, light from
the Sun strikes the
ground more directly,
concentrating the
Sun’s energy.
• Summers are therefore
warmer than winters.
Precession I
• The Earth spins about its axis like a top, but the Sun’s gravity
adds a pull that causes it to “wobble”.
• This wobble means the axis of the Earth is rotating, or
precessing, with a 26,000 year period.
Precession II
• Because of this
precession, Polaris
(the North Star) has
not always been and
will not always be
“The North Star”.
• 6000 years ago, the
North Star was
Thuban, a star in the
constellation Draco.
• In 12,000 years, the
Earth’s axis will point
toward Vega, a bright
star in Lyra.