Transcript ppt document

Star Chart
The small brass ring in the
middle is the location
of the North Star.
The “railroad
tracks” around
the North Star
are the positions
of the sun at
different days and
form the ecliptic.
Note that the ecliptic is
a circle, but the North
Star is not at it’s
center but is offset.
Star Chart
The previous picture, if lifted above your
head, is what the sky would look like if you
were at the North pole. We could only see
to the horizon which would be a circle
centered on the North Star that would
extend to about 2/3 of the radius in the
picture (the pink circle on the next slide).
Star Chart
Note that the
constellations of
the zodiac (e.g. Leo,
Sagittarius,
and Gemini,) are
found along
the “railroad
tracks” (along
the ecliptic). In
fact, it is that location
along the ecliptic that
makes these
constellations
special.
Star Chart
The stars seem to circle around the North Star with
a period of just under 24 hours.
If we are at some other location in the Northern
Hemisphere, our zenith (point straight overhead)
would move. When we put the flap of the star
chart down as we do in the next slide, we see
what the sky would look like from a latitude of
about 40 degrees North. (Memphis has a
latitude of 35 degrees North.)
Scroll around to see more of the chart.
If you match up the time of day with the day of the
year, this is the way the sky will look like at that
time on that day.
Star Chart - directions
You may have noticed that the North
direction is at the top of the picture as
usual, but that the East direction was on
the left rather than the right. This is
because the chart is to be used above
your head rather than down on the desk.
If you lift the chart above your head and
point the North arrow toward the North,
you will find that the East direction does
match the East marking on the chart.
Positions of the sun
Sun at noon
on Dec. 21
in Sagittarius.
Compare this
position to
that of the
sun on June
21 on the
next slide.
Positions of the sun
Sun at noon
on June 21.
Note that the
sun appears
in Gemini
and above (to
the North of)
Orion.
The sun is much
higher in the
sky in summer
than in winter.
Positions of the Sun
Here we see
the sun on
the Western
horizon
(sunset) in
in Gemini
on June 21
a little after
7 PM CST.
Notice that the
sun sets well
North of West.
Positions of the Sun
Compare the
position of
the setting sun
in Sagittarius
on Dec. 21 it happens
about 4:30 PM
and is
quite a bit
South of due
West.
Motions of the Sun
If you play with the star chart, you will see
that in the winter months, the sun rises
South of East just like it sets South of
West. You will also see that in the
summer months the sun rises North of
East just like it sets North of West. In the
summer, the sun is in the sky longer and is
also higher in the sky than in winter.
Positions of the sun
Note that in
June, the sun
is in Gemini,
but in July it
moves toward
Cancer and then
in August it moves
toward Leo.
The sun moves across
the sky from East
to West, but it
moves through the
constellations of
the zodiac from
West to East!