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Slide 1

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OCR GCSE Physics P7
Topic 1 ­ Naked Eye Astronomy…read more

Slide 2

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Seasonal Changes of Stars in the
Night Sky
· Stars that can be seen in the
Northern Hemisphere can't
(generally) be seen in the Southern
Hemisphere and visa versa.
· If you want to see the stars in the
Northern Hemisphere at the same
time then you have to go to the
equator (obviously you won't be able
to see all of the stars but you do get
a good viewing of both ­ a sort of
· Each day a star rises 4 minutes earlier. This means that a star that rises at
dusk in June will set at dusk in December. This is because over 6 months the
4 minutes add up to 12 hours.
· You will see different stars in the winter to those you see in the summer. This
is because you are looking out in a different direction.…read more

Slide 3

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Apparent Motion of the Sun, Moon
and Stars
· Takes 365 days for Earth to orbit the Sun
· A solar day is 24 hours
· A sidereal day (the star equivalent of the Sun's day) is 23 hours and 56
· The Moon orbits the Earth in 28 days and re-appears every 24 hours and 49
· The phase of the Moon depends on where it is in it's orbit and from what
direction the Sun's light is coming from…read more

Slide 4

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· From Earth you can seen five planets with the naked eye (or in normal talk ­
without a telescope) ­ these are Mercury, Venus, Mars, Jupiter and Saturn
· Some of the planets appear to move forward and then backwards ­ this is
known as retrograde motion
· The reason the planets appears to do this is because they are view from
earth against a back drop of stars (which don't move)
· All planets that are orbiting our Sun do so on roughly the same plain (same
level and angle of tilt)
· Some planets take longer to orbit than others ­ this is generally because
they are further away.…read more

Slide 5

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Eclipses ­ Lunar and Solar
· A lunar eclipse is when the Moon moves into the Earth's umbra
· A solar eclipse is when the Moon blocks the Sun's light ­ then the Moon's
umbra touches Earth's surface
· To see a solar eclipse the Sun and the Moon has to be travelling at the
same height
· An umbra is a region of total darkness
· A penumbra is a region of partial darkness…read more

Slide 6

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Finding a Star
· Stars can be positioned by angles
· To give an angle to a star you use the Equatorial co-ordinate system ­ this
uses a point of reference in the sky which is the Vernal Equinox
· This point can be used by anyone in the world (which is why it is used
because it is universal (uuurrrrggghhh!! )
· This position is defined by two angles ­ right ascension and declination…read more


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