Transcript SNC 1D Astonomy

The Night Sky
Ancient Astronomy
• Early astronomers paid attention to the sky
and were careful to not offend the gods that
rule the skies.
• The time it takes for the Earth to make one
revolution around the sun is 365.24 days.
• It takes one day for Earth to make one
rotation on its axis.
• The first clocks were pillars and sticks in the
ground and people used the shadows they
made to tell the time.
Patterns in the Night Sky
• Many groups of stars seem to form patterns
called constellations.
• They appear to lie very close to each other at
exactly the same distance from Earth.
• They look close together because they lie on
the same line of sight.
• They may actually be many light years apart!
• One light year is a unit of distance, it is the
distance light travels in one year. (9.5 x
1012km)
What constellation is this?
Random stars in space
Apparent Magnitude
• Star maps show
constellations and
individual stars.
• The larger the dot on
the map, the larger
the star appears to us
on Earth.
• Apparent magnitude
is the brightness of a
star as seen from
Earth
Names of Constellations
• The International Astronomical Union (IAU) is
responsible for naming and classifying
celestial objects.
• There are 88 official constellations.
• Examples are cancer (crab), Cassiopeia (the
queen), Ursa Minor (Little Bear)
• Smaller groups of stars that form patterns
within a constellation are called asterisms.
• Example is the Big Dipper (a part of the Ursa
Major, the Great Bear)
What is this constellation?
• Ursa Major
• Cassiopeia
Polaris and Pointer Stars
• The Big Dipper’s
two end-stars
are called the
pointer stars
because they
point toward
Polaris (North
Star)
Rotation
Revolution
Earth’s Motion
• The Moon is responsible
for the tides (rising and
falling of ocean waters)
that occur on Earth.
• Due to the Earth revolving
around the Sun, we see
different constellations at
different times of the year.
• The path of the Earth’s
orbit around the Sun is not
a perfect circle, it is an
ellipse.
Seasons
• Earth rotates at a tilt
of 23.5.
• In the summer
months, the
northern
hemisphere is tilted
toward the Sun.
• Sunlight strikes
Earth at different
angles
THE MOON
• the moon orbits Earth every 29.5 days
• the moon rotates once on its axis as it
completes one orbit around Earth
• as a result, we see only one side of the moon
THE MOON
• the moon is always half illuminated by the Sun
• the amount of illumination we see is classified
as the phases of the moon
FOUR MAIN SHAPES
FULL
QUARTER
CRESCENT
GIBBOUS
Moon Phases
Waxing - increasing
Waning - decreasing
Name this phase!
Full Moon
Name this phase!
First Quarter
Name this phase!
Waxing Crescent
Name this phase!
Waning
Gibbous
Name this
phase!
Third Quarter
Name this phase!
Waxing Gibbous
Name this phase!
Waning Crescent
Name this phase!
New Moon
Name this
phase!
Waning Crescent
Waxing Crescent
WHAT’S A BLUE MOON?
• A great doo-wop song from the 50s!
http://www.youtube.com/watch?v=gzG7bPRZvMk
• An extra full moon that happens every 2.72 years.
LUNAR ECLIPSE
Earth’s shadow is divided into 2 parts: the umbra (inner
shadow) and the penumbra (outer shadow).
SOLAR ECLIPSE
Occurs whenever the shadow of the Moon falls
on Earth’s surface, the Moon is between the
Sun and the Earth.
SOLAR ECLIPSE