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Chapter 1:Charting the Heavens…The Foundations of Astronomy
1.1 Our place in space
o Is Earth, compared to the rest of the universe, considered to be unique or special?
YES or NO
Definitions & Key Points:
o Universe: the totality of all space, time, matter, and energy
o Astronomy: study of the universe
o Light Years: distance traveled by light, at speed of 300,000 km per second, in one
year
Why is Astronomy a subject unlike any other (in other words, why is it difficult for us to
study)? Because it’s measured on a scale that’s unfamiliar to us
1.2 The Obvious View
Definitions & Key Points:
o Constellations: a human grouping of stars in the night sky into a recognizable
pattern (example – Orion)
 How did early Astronomers use constellations?
-used them as a navigational guide
 How do Astronomers use Polaris (what does this star tell them)?
-to find north (a.k.a the North Star)
o Celestial Sphere: imaginary sphere surrounding Earth, to which all objects in the
sky were once considered to be attached (figure 1.7)
 Constellations appear to do what over the course of a night?
-appear to move across the sky (east to west)
 True or False: Early Astronomers pictured the stars to move with the
celestial sphere as it turned around a fixed, unmoving Earth. Give evidence
of your answer:
o Rotation: the apparent motion of the stars as a result of the spin of the Earth
o North Celestial Pole: point on the celestial sphere directly above Earth’s North
Pole
o South Celestial Pole: point on the celestial sphere directly above Earth’s South
Pole
o Celestial Equator: the projection of Earth’s equator onto the celestial sphere
1.3 The Motion of the Sun and the Stars
Day-to-Day Changes
Definitions & Key Points:
o Solar Day: period of time between the instant when the Sun is directly overhead
(noon) to the next time it is directly overhead
 What do we measure time by?
-SUN
o The celestial sphere seems to “shift” a little relative to the horizon, compared to
the night before
o The easiest way to confirm this shift, or difference, is by noticing the stars
that are visible just after sunset or just before dawn. You will find that
they are in a slightly different locations from those of the previous night
(sidereal day)
o Sidereal Day: a day measured by the stars
 Does a sidereal day differ in length from a solar day? YES or NO
***The reason for the difference between a solar day and a sidereal day is the fact that
Earth moves in 2 ways simultaneously:
1. Rotates on its central axis
2. Revolves around the Sun
o Revolve: orbital motion of one body about another (example: Earth around the
Sun)
Seasonal Changes
o Ecliptic: apparent path of the Sun, relative to the stars on the celestial
sphere, over the course of one year
o Summer Solstice: point on the ecliptic where the Sun is at its northernmost
point above the celestial equator
 When does it occur? ~June 21st
o Winter Solstice: point on the ecliptic where the Sun is at its southernmost
point below the celestial equator
 When does it occur? ~December 21st
o Seasons: change in average temperature and length of day that results from
the tilt of Earth’s axis with respect to the plane of orbit (page 12, fig. 1.10)
o Equinoxes: the 2 points where the ecliptic intersects the celestial equator
(equal day & night)
o Autumnal Equinox: date on which the Sun crosses the celestial equator
moving southward
 When does it occur? September 21st
o Vernal Equinox: date on which the Sun crosses the celestial equator moving
northward
 When does it occur? March 21st
o Tropical Year: interval of time from one vernal equinox to the next
(365.242 days)
Summer and Winter Constellations
o Zodiac: The 12 constellations on the celestial sphere through which the Sun
appears to pass during the course of a year.
o Sidereal Year: The time required for the constellations to complete one cycle
around the sky and return to their starting points, as seen from a given point on
Earth. Earth’s orbital period around the Sun is one sidereal year.
 Earth’s orbital period across the Sun = Sidereal Year
Long-Term Changes
Earth has MANY motions:
1) Spins on its axis
2) Travels around the Sun (orbits the sun)
3) Moves with the Sun through the galaxy
These motions can account for the changing nighttime sky and the changing seasons!
4) Precession: Earth’s axis changes its direction over the course of time
(picture a spinning top-for further explanation read p.14)
Lunar Phases
 The moon is our nearest neighbor in space.
 The moon DOES revolve around the Earth.
o Phases: the changes in the Moon’s appearance, occurs in a regular cycle taking a
little more than 29 days to complete (Word month is derived from the word Moon)
o New Moon: cycle starts here, Moon is NOT visible in the sky
 From here the Moon begins to wax (or grow) a little each night and is visible as a
growing crescent
o Quarter Moon: one week after new moon, half of the lunar disk can be seen
 Moon continues to wax, passing through the gibbous phase
o Full Moon: 2 weeks after new moon, the complete lunar disk is visible in the sky
 During the next 2 weeks the Moon wanes (or shrinks), passing in turn through the
gibbous, quarter, and crescent phases, eventually becoming new again.
 Great figure for reference to understand the lunar phases is on page 15 (Figure
1.14)!! Make sure to review and completely understand figure 1.14.
 Know where the sun is located
 Know where the Earth is located
 And where the Moon is located in each phase!!!!
o Sidereal Month: time required for the Moon to complete one trip around the
celestial sphere (27.3 days)
o Synodic Month: time required for the Moon to complete a full cycle of phases
(~29.5 days)
 How long does the Synodic month take?

Synodic Month is a little longer than the sidereal month for the same
reason that a solar day is slightly longer than a sidereal day: because of
Earth’s motion around the Sun, the Moon must complete slightly more
than one full revolution to return to the same phase in its orbit.
Eclipses
o Eclipse: Event during which one body passes in front of another, so that the light
from the occulted body is blocked.
o Lunar Eclipse: Celestial event during which the Moon passes through the
shadow of Earth, temporarily darkening its surface (p.18 & 19)
o Solar Eclipse: Celestial event during which the new Moon passes directly
between Earth and the Sun, temporarily blocking the Sun’s light. (p. 18 & 19)
o Partial Lunar/Solar Eclipse: part of the occulated (illuminated) body is
blocked from view
o Total Lunar/Solar Eclipse: body is completely blocked from view by another
**Unlike a lunar eclipse, which is simultaneously visible from all locations on Earth’s night
side, a total solar eclipse can be seen from only a small portion of Earth’s daytime side.
o Annular Eclipse: Solar eclipse occurring at a time when the Moon is far enough
away from Earth that it fails to cover the disk of the Sun completely, leaving a ring
of sunlight visible around its edge.
1.5 The Measurement of Distance
Definitions and Key Points:
o Cosmic Distance Scales: Collection of indirect distance-measurement techniques
that astronomers use to measure distances in the universe.

Triangulation: Method of determining distance based on the principles of
geometry. A distant object is sighted from two well-separated locations.
The distance between the two locations and the angle between the line
joining them and the line to the distant object are all that are necessary to
ascertain the object’s distance. (Visualizing an imaginary triangle)

Parallax: The apparent motion of a relatively close object with respect to a
more distant background as the location of the observer changes.