Zusammenfassung der Ressource
P7: Naked Eye Astronomy
- The Earth Rotates on its axis
- It does this West to
East once in just
under 24 hours
- This causes the stars
to appear to move
East to West in the
same amount of time
- The sun, planets and moon also
appear to move east to west across
the sky, however the time they take to
do this depends on their individual
orbits
- The sun appears to
travel across the sky
once every 24 hrs
- A sidereal day is the time it
takes for the earth to rotate
360 degrees on its axis
- A solar day is the time from
noon one day, to noon the next
(i.e. 24 hrs)
- The earth orbits the
sun as well as
rotating on its axis
- It is this that makes the sidereal
day 4 minutes shorter that a
solar day
- Different stars can be seen
at different times of the year,
depending on the position of
the earth in the suns orbit
- The Position of Astronomical Objects
- The position of astronomical
objects can be measured in
terms of angles as seen from
the earth.
- Angles of "Declination" and "Right
Ascension" describe the positions of stars
in relation to a fixed point on the equator
- Declination is measured south and north of the Equator
- A star with Positive declination will be
visible form the northern
hemisphere
- A star with Negative Declination will be
visible from the southern
hemisphere
- Right ascension is measured around the celestial equator
- Planets can be seen from earth with the
naked eye, they look similar to stars but
change their positions in a complicated
pattern
- When compared to backgrounds of fixed
stars, planets appear ti move with a
retrograde motion
- This is because the earths smaller
orbit causes it to overtake each of
the outer planets at different times
of the year.
- This causes these planets to slow down against
the star background and go into reverse
- Retrograde motion- The apparent backwards motion
of planets from west to east due to the combined
motion of earth and the planets
- The Moon
- Whilst the Earth is rotating on its axis, the moon
is orbiting the Earth in the same direction
- Due to this, the moon appears to be moving East to West
across the sky in a little over 24 hours, faster than the earth
- The Lunar Cycle describes the moons
appearance during its 28 day orbit
- The moons shape during its orbit is due
to the part of the moon that is visible to
the earth
- We are able to see the moon
because of the suns light
reflecting off it
- The side facing away from the sun appears dark
- The side facing towards the sun appears light
- Eclipses
- Solar Eclipse
- This occurs when the moon
passes between the earth and the
sun
- This results in the moon casting a shadow
on the earth
- Total Solar Eclipse
- Occurs when the moon is directly in front
of the sun and completely obscures the
earths view of the sun
- Lunar Eclipse
- Occurs when the earth is
between the sun and the
moon
- Results in the Earth casting a shadow
on the moon
- Lunar eclipses don't occur every month
because the moon orbits the earth at a 5
degree angle to that of the earths orbit of the
sun
- An eclipse can only occur when the
moon passes through the ecliptic ( the
apparent path the sunlight traces out
along the sky)
- There are between 2 and 5 solar eclipses
ever year
- A total eclipse will only
occur roughly ever 18
months