SCCC 115 - Descriptive Astronomy

Need textbook (Chaisson and McMillian) and Study Guide (John Safko)

Need lab book

Calculator (with scientific notation, log, trig functions)

New Syllabus

Sunday Lab schedule

Bring to class: textbook, calculator, pencil, and paper

What is Astronomy ?

Group Interaction: Make a list of generalizations about what Astronomy is according to our textbook.

What is Astronomy? Some Thoughts

The study of the universe

The universe is space, time, matter, and energy

Emphasizes the concentration of energy and matter into stars, planets, and Galaxies

Earth is one of many places in the universe

Earth is our vantage point from which to study the universe

Charting the HeavensObjectives

Explain how we locate objects in the sky: time and angular measure

Describe the positions of the Sun, Moon, and stars and how they appear in the sky

Account for apparent motions in terms of the actual motions of the Earth and Moon

Motions of Earth and Moon lead to eclipses

How we measure distances and sizes of faraway objects

Units

MKS system: meters, kilograms, and seconds

Speed of light = c=300,000 km/s=186,000 miles/s

Light year= ly=the distance light travels in one year

Time

Angular measure: degrees, arcminutes, arcseconds

Scale

Scientific Notation

Motion of Earth

Earth revolves around the Sun

Earth rotates about once per day

Earth's rotation axis is tilted 23.5 degrees from vertical

Moon revolves around the Earth

Lunar phases

Moon's revolution and rotation rate are equal

Synodic month = time required to complete a full cycle of phases, 29.5 days

Lunar Phases

Moon's revolution and rotation rate are equal

Synodic month = time required to complete a full cycle of phases, 29.5 days

Eclipses

Lunar and Solar

Total, partial, annular

Shadow: umbra and penumbra

Eclipse season

Fig. 1.19, 1.20

Eclipse Seasons and Tracks

Moon's orbit is inclined 5 to ecliptic

Eclipse season

Fig. 1.21, 1.22 (only umbra shown)

Celestial Sphere

Celestial poles and celestial equator

Ecliptic, zodiac, zenith, and meridian

Equinoxes (vernal, autumnal) and Solstices (summer, winter)

Seasons

Precession

Horizon and Altitude, Right Ascension and Declination

Precession

Rotation of Earth's axis

Takes 26,000 years for one rotation

Fig. 1.14

Time

Tropical year 365.242 days

Solar year-365 (average) solar days, 1day=24 hours

Sidereal - relative to the stars 365.256 days

Julian Calendar 46 B.C.- leap year: added an extra day every 4 years, much improved over earlier lunar calendars

Gregorian Calendar 1582 A.D. (adopted by Britain and the American Colonies in 1752) - omit extra day in years that are multiples of 100, except if a multiple of 400

Sidereal vs. Synodic

Synodic- For Moon: One full cycle of phases 29.5 days

Sidereal - Relative to the stars 27.3 days

Fig. 1.10, 1.16

Parallax

Apparent displacement of a foreground object relative to background objects

Fig. 1.25

Angular Measure

Geometry

Fig. 1.23, 1.24

Small Angle Equation

More Precisely 1-4

Diameter= distance X angular diameter/57.3^°

D=d alpha / 57.3^°