The textbook web resources for Chapter 1 are here.
Sphere - an imaginary globe that surrounds the Earth and contains the
stars, planets, sun, moon, etc. This is not really the case, but we can think
about the sky this way because the stars are so far away and seem to travel
As we observe the sky, the sun, stars, moon, and planets seem
to rise in the east and set in the west. This is due to the Earth's
rotation (spin on its axis). Stars rise 3 min, 56 sec earlier
each night, which adds up to 24 hours over the course of the
Different constellations are visible at different times of the
year. For example, Orion is a winter constellation. This is due to the Earth's
revolution (orbit around the sun).
planet comes from a Greek word that means "wanderer". This is
because the planets seem to move aross the Celestial Sphere separately from the
stars. They move along a path that follows the ecliptic (the
path that the sun follows along the Celestial Sphere). This path that the
planets follow is called the zodiac, and it crossed the 12
zodiac constellations: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra,
Scorpius, Sagittarius, Capricornus, Aquarius, and Pisces.
slower across the sky than stars do, because they are travelling around the sun
with us - similar to a car that is travelling alongside you on the highway. The
car may be going faster or slower than your car, but it will seem to pass us
slower than the surrounding landscape will.
Planets also display
retrograde motion. This means that they sometimes appear to
reverse their direction as they travel across the Celestial Sphere. This
happens when Earth and the other planets pass each other.
moon also moves across the Celestial Sphere. It moves a
distance about equal to its diameter in the sky every hour, and makes one
revolution around the Earth in about 30 days. As it goes around the Earth, it
displays different phases - meaning that we see different
amounts of its face lit up. Phases include
new moon (completely dark), waxing
crescent, first quarter,
waxing gibbous, full moon
(completely lit), waning gibbous, third
quarter, waning crescent, and back to new moon.
Waxing means that the lit portion of the moon is growing
larger (as the moon becomes more full). Waning means that the
lit portion is growing smaller. We tend to see the full moon all night long,
while the crescent moon is out during the day (extending into early morning and
Because Earth is rotating as the moon goes around it, the
moon seems to rise 50 min later each day.
when the sun, Earth and moon all line up and the shadow of the Earth or the moon
falls on the other. These do not happen every month because the moon's orbit
around the Earth is tilted about 5 degrees to the Earth's orbit around the
Kepler's Laws of Planetary Motion
- Law of Ellipses
Law of Equal Areas
- Planets move in elliptical orbits with the Sun at one focus of the ellipse.
Law of Periods
- The orbital speed of a planet varies so that a line joining the Sun and the planet will sweep over equal areas in equal time intervals.
- The amount of time a planet takes to orbit the Sun is related to the orbit’s size, such that the Period (P) squared is proportional to the semimajor axis (a) cubed. The formula for this is: P2 = a3
Homework from the
- Read Chapter 1.
- Review Questions #1-11 on page