INTRODUCTION TO ASTRONOMY

Astronomy--the science dealing with the Universe (by definition, everything there is)

Cosmology--branch of astronomy that deals with the cosmos, or Universe as a whole.

Astrology--a form of fortune-telling unrelated to science or astronomy

ASTRONOMICAL MEASUREMENTS

Metric system:

• Units of length:

  kilometer (km) 6/10 mile(mi).
  meter (m) 1 yd. 4 in.
  centimeter (cm) 4/10 in

• Unit of mass: kilogram (kg). 1 kg weighs 2.2 lbs. (lb.=unit of weight)

• Unit of time: seconds, same as English system.

• Angles: degrees.

  1° = 60' (minutes of arc, arc minutes)
  1' = 60" (seconds of arc, arc seconds)

Note the difference between visual angle (apparent size) and actual size. Which is bigger, the horse or the church?

POWERS OF TEN, or scientific notation

"x 10⁸" says "multliply by 10 eight times," e.g. 3x10⁸ kg = 300,000,000 kg

"x 10^-6" says "divide by 10 six times," e.g. 2x10^-6 m = 0.000002 m

the exponent is called order of magnitude

You can represent powers of ten in computer spreadsheet programs. The preceding examples would be entered as 3.0E8 and 2.0E-06 respectively. Scientific calculators have a button marked EE or EEX that serves the same purpose.

OTHER UNITS

light year 1 ly = distance travelled by light in one year 10¹³ km.

A light year is a unit of distance, not time.

parsec 1 pc 3.3 ly

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