Transcript 2 Measurements in Astronomy

Measurements in Astronomy
For really, really big
and faraway things!!!
U.S. Customary (English Units)
Units of Distance
 Inch – good for measuring little things, like a
pencil (thumb)
 Foot – 12 inches – good for measuring things
like a room or a car (human foot)
 Yard – 3 feet – good for measuring things like
a swimming pool or a football field (nose to
finger)
 Mile – 1760 yards or 5280 feet – good for
measuring distances between cities (1000
paces of Roman Legion)
 We’re used to thinking in these
measurements, but it’s much harder
to do calculations between them.
Who wants to divide by 12 or multiply
by 1760? Not you, I bet! That’s why
metric is awesome!!!
The Metric System
 Also called the International System
of Measurement – Why? Because
every other country in the world uses
it!
 If you know the prefixes of metric
words, you’ll know how to convert
between different units.
Prefixes to know
 Centi = 100 (cents in a dollar, years in a
century)
 Milli = 1000 (years in a millenium)
 Kilo = 1000 (but kilo is really big, and
milli is really small)
 So…
 1000 millimeters in a meter
 100 centimeters in a meter
 1000 meters in a kilometer
Metric System Chart
mnemonic Metric
Conversion
King
Kilometer
1,000 m
Henry
Hectometer 100 m
Dies
Dekameter
While
Standard
(meter, liter,
gram)
Drinking
Scientific
Notation
10 3
10
2
10 m
10
1
1m
10
0
Decimeter .1 m
10
-1
Chocolate
centimeter .01 m
10
-2
Milk
millimeter .001 m
10
-3
FYI
 Prefixes in metric are not just used
for distance (meters). They are also
used for mass (grams) and volume
(liters) too! Isn’t that easy?!?
Scientific Notation
 Helps scientists make really, really big
and really, really small numbers
easier to write.
 Who wants to write
1,700,000,000,000,000,000,000,000
when you can write 1.7 x 1024, or
0.0000000000000000000000000002
when you can write 2 x 10-28?
Skill Builder: Scientific Notation
 Follow the four steps in the skill
builder to fill in the chart on page 1,
then answer the questions under
part 2.
Measurements in Astronomy
 Astronomical unit: distance from Earth
to the Sun (about 150,000,000
kilometers, or 93,000,000 miles). Used
for measuring distances within our solar
system.
 Light year: the distance light travels in
one year (nearly 10 trillion kilometers or
6 trillion miles). Used for measuring
distances between stars and galaxies.
 Parsec: 3.26 light years
How do astronomers measure
distances?
 For nearby stars
(distances less
than 500 light
years),
astronomers use
parallax.
 Parallax is the
apparent change in
position of an
object when you
look at it from
different directions.
How do astronomers measure
distances?
 For stars that are further
away, astronomers use the
inverse square law.
 Inverse square law states
that apparent brightness is
inversely proportional to the
square of the distance.
 If you know how bright the
star should be, and you
know how bright it appears
to be, you can calculate how
far away it is.
1. The prefix centi means?
1,000
10
100
1
90%
10%
1
0
0%
10
10
00
0%
10
A.
B.
C.
D.
2. Which metric unit is the largest?
Milli
Kilo
Centi
hecto
87%
4%
ct
o
ti
en
C
ilo
K
ill
i
0%
he
9%
M
A.
B.
C.
D.
3. Writing millimeter in scientific
notation is:
103
101
10-1
10-3
74%
26%
-3
10
-1
0%
10
1
10
3
0%
10
A.
B.
C.
D.
4. The measurement used to find the
distance between the earth and the sun
and other planets in our solar system is:
Parsec
Kilometer
Astronomical unit
Light year
48%
39%
13%
A
ar
...
Li
gh
t
ye
lu
om
ic
a
st
ro
n
K
ilo
rs
e
c
m
et
er
0%
Pa
A.
B.
C.
D.
5. ____ is used to measure the
distances between stars and galaxies.
Parsec
Light year
Astronomical unit
miles
100%
om
ic
a
st
ro
n
A
ile
s
ye
gh
t
Li
lu
ar
c
rs
e
0%
m
0%
...
0%
Pa
A.
B.
C.
D.
6. When stars are less than 500 light
years away astronomers use this
method:
A. Astronomical
distances
B. Spectrometers
C. Inverse square
law
D. parallax
74%
22%
In
pa
ra
l
la
x
..
re
.
ve
rs
e
sq
ua
tro
m
et
er
Sp
ec
ld
om
ic
a
st
ro
n
A
0%
s
...
4%
7. A ____ is the longest unit to
measure astronomical distances.
A. Parsec
B. Inverse square
law
C. Parallax
D. Light year
40%
40%
15%
In
ve
rs
ar
gh
t
ye
la
x
ra
l
Pa
Li
e
Pa
sq
ua
rs
e
re
.
c
..
5%
8. When stars are more than 500 light years away
astronomers rely on calculating the apparent vs.
absolute brightness called:
A. Parallax
B. Parsec
C. Inverse square
law
D. spectrometer
87%
13%
er
..
0%
sp
e
ve
rs
In
ec
sq
ua
tro
m
et
re
.
c
rs
e
Pa
Pa
ra
l
la
x
0%