Download 3 x 10 5

NUMBERS IN ASTRONOMY
See Appendix 4 & 5
NUMBERS in ASTRONOMY

Some numbers are very small
E.g. Diameter of Hydrogen Atom is about 0.00000001 cm
.0000000000001 cm
Proton
Electron
.00000001 cm
Hydrogen Atom
NUMBERS in ASTRONOMY

Some numbers are very small
E.g. Diameter of Hydrogen Atom is 0.00000001 cm

Other numbers are very large
 E.g. size of galaxy 100,000,000,000,000,000,000,000 cm
NUMBERS in ASTRONOMY

Some numbers are very small
E.g. size of Hydrogen Atom (GS) is 0.00000001 cm

Other numbers are very large
E.g. size of galaxy 100,000,000,000,000,000,000,000 cm

Powers of 10 Notation
 The number of zeros is denoted by an exponent of 10.
 This exponent is positive if the number is larger than 1.
10N is 1 followed by N zeros
 E.g. 100,000,000,000,000,000,000,000 is written as 1023
 The exponent (power) is negative if the number is smaller
than 1.
10-N represents a 1 in the Nth place after the decimal
E.g. 0.00000001 is written as 10-8
POWERS OF 10 NOTATION

10N is 1 followed by N zeros

10-N is a 1 in the Nth decimal place after the
decimal point
 103 is 1000
 108 is 100,000,000
 10-3 is 0.001
 10-8 is 0.00000001

More complicated numbers are represented by
a combination of a power of 10 and a
multiplying factor
 0.000000025 is 2.5 x 10-8
 64,000 is 6.4 x 104
NUMBERS IN ASTRONOMY

Rule for Multiplication
 Multiply the factors and add the powers
4
10
5
10
E.g. 2 x
times 3 x
(4+5)
9
is (2x3) x 10
= 6 x 10

Rule for Division
 Divide the factors and subtract the powers
E.g. 5 x 106 divided by 2 x 104 is
(52) x 10(6-4) = 2.5 x 102
TEST YOURSELF

The mass of the Sun is:
1,989,000,000,000,000,000,000,000,000,000 kg.
Write this mass in the powers-of-ten
notation.

Answer: 1.989 x 1030 kg
FLASHCARD
The Gross National Product of Canada in
2000 was 7.6 x 1011 Canadian Dollars.
There are 3 x 107 people in Canada. What
is the amount of GNP per person?
A) 2.5 x 103
B) 2.5 x 104
C) 2.5 x 105
D) 2.5 x 106
FLASHCARD
The centre of our Galaxy is 7 x 1016 km
from us. UNBC (in Prince George) is
about 5 x 102 km away from us. How
many times farther (in powers of 10
notation) is the Galactic centre from us
compared to UNBC?
A) 3.5 x 1019
B) 1.4 x 108
C) 1.4 x 1014
D) 7.1 x 10-15
FLASHCARD
The mass of our Galaxy is about 7 x 1011
times the mass of our Sun. There are
about 1011 galaxies in the Universe. If an
average star weighs about half that of
our Sun, about how many stars are there
in the Universe?
A) 7 x 10121
B) 14 x 1022
C) 7 x 1022
D) 7
POWERS of TEN EXAMPLES
Sizes in Meters
UNITS in ASTRONOMY
Mass: kilograms (kg)
 Time: seconds (s) or years (y)
 Distance: meters (m), kilometers (km), light
years (ly), or Astronomical Units (AU)

 A light year is the distance light travels in one
year
Speed of light = 3 x 105 km/s
There are 3 x 107 seconds in a year
Thus a lightyear is (3 x 105) x (3 x 107) = 9 x 1012 km
 An Astronomical Unit is the mean distance
between Earth and the Sun (1.5 x 108 km)
UNITS in ASTRONOMY

Light year:
 This is the distance which light will travel in the
period of 1 year
 The speed of light (c) is 3 x 105 km/s
 There are 3 x 107 seconds in a year
 Thus, a light year is (3 x 105) x (3 x 107) = 9 x 1012 km
 Note: the star nearest the Sun (Proxima Centauri)
lies at a distance of 4.26 ly (or 38 million million km!)

Astronomical Unit:

Solar Mass
 This is the mean Earth-Sun distance, and is about
1.5 x 108 km ( 150 million km)
 This is a convenient unit to use for mass and is
equal to the mass of our own Sun (1.9891 x 1030 kg)
 Your instructor weighs in at a hefty 4 x 10-29 solar
masses
UNITS in ASTRONOMY

Temperature:






Use Degrees Kelvin (K)
K = C + 273
C water freezes at 0C boils at 100C
K water freezes at 273K boils at 373K
Room Temperature about 300K
0K = - 273C is absolute 0
ANGULAR MEASUREMENT
360
0° degrees
270 degrees
90 degrees
180 degrees
ANGULAR MEASUREMENT
360 degrees in a full circle
1 degree = 60 minutes
1 minute = 60 seconds
ANGULAR MEASUREMENT
FLASHCARD
WHAT IS THE ANGULAR SIZE OF THE
MOON AS SEEN FROM THE EARTH?
A) 0.5 degree
B) 5 degrees
C) 10 degrees
D) 50 degrees