Physics 162 Elementary Astronomy

1
Physics 162Elementary Astronomy

• Dr. Fortner
• FW 204 MWF
• mfortner_at_niu.edu

2
Web Pages

• My Page www.niu.edu/mfortner/
• PHYS 162 syllabus and lectures
  nicadd.niu.edu/fortner/course/phys162/
• Webassign www.webassign.net
• Observatory www.niu.edu/physics/observatory/

3
Course Topics

• The course is divided into four broad topics.
• Foundations - Tools and rules
• Planets - Earth and its neighbors
• Stars - How the sun and other stars work
• Universe - Galaxies and beyond
• Each topic includes a written assignment and a
  test.
• Each week includes an online homework assignment.

4
Why Astronomy?

• Astronomy is as old as humans have looked up at
  the sky.
• Astronomy is the science of stars and other
  objects in space.
• Physics, chemistry, geology, even some biology
• Laboratory for conditions beyond earth-based
  experiments
• Astronomy remains newsworthy today.
• News stories from NASA and other countries
• Movies and popular culture

5
Measurement and Units

• Scientific measurement requires standard units.
• English units foot, pound, second
• Metric units meter (m), kilogram (kg), second
  (s)
• Derived units cubic meter (m3), watt (W)
• Alternate units hour (h), light year (ly)
• The metric system has two major strengths.
• Widespread use in science
• Prefixes based on powers of ten

6
Scientific Notation

• In science some measurements can be very large or
  very small compared to the base unit.
• Scientific notation uses powers of 10 to
  represent decimal places.
• Positive for large values 456000 4.56 x 105
• Negative for small values 0.00753 7.53 x 10-3
  (only one non-zero value to the left of the
  decimal place)

7
SI Prefixes

• Prefixes on units are used to represent powers of
  ten.
• Prefixes denote powers of ten from -18 to 18
  mostly in steps of three.
• For example a kilometer (km) is 103 meters or
  1000 meters.

• Most Common
• nano (n) 10-9
• micro (?) 10-6
• milli (m) 10-3
• centi (c) 10-2
• kilo (k) 103
• mega (M) 106
• giga(G) 109
• Common, but the power is not a factor of three.

8
Unit Conversion

• Conversion between units must be of the same type
• Length conversion 1 in 2.54 cm
• Time conversion 1 h 3.6 x 103 s
• No conversion between different types of units.
• 1 m3 not equivalent to any number of m

9
Significant Figures

• Any value is expressed in some number of digits.
• The number of digits (without left side zeroes)
  is the number of significant figures.
• With no decimal point, skip right side zeroes.
• 38 2 digits, 2 significant figures
• 5.06 3 digits, 3 significant figures
• 0.0041 5 digits, 2 significant figures
• 7,000. 4 digits, 4 significant figures
• 2,000 4 digits, 1 significant figure

10
One Ton
Assume the density of a rock is three times that
of water. How many centimeters across is a one
metric ton (1000 kg) rock?

• The rock has a density of 3 x 103 kg/m3.
• The volume is
• 103 kg/(3 x 103 kg/m3)0.3 m3
• Estimate that the rock is a sphere, V (4/3) ?
  r3
• d 2r 2 (3V/4 ?)1/3
• d 0.9 m x 100 cm/m 90 cm