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P7 Observing the Universe

P7.1 Observing the sky with the naked eye

THE SOLAR SYSTEM

The solar system is the collection of planets, comets, and all other objects that orbit the sum. The sun
is a medium sized star.

The earth take 365.25 days to complete one orbit we call…

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ECLIPSES

Eclipses happen with light from the sun is blocked

There are two types of eclipses. Lunar eclipse and Solar eclipse.

Lunar eclipse
As the moon orbit the Earth, sometimes it passes into the Earth's shadow. The Earth blocks sunlight
from the Moon, so almost no light reflected form the…

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Eclipses do not happen that frequently. This is because the moon actually orbits the Earth at a tilt which
means that most of the time, the moon won't line up to cause a lunar or solar eclipse. Partial eclipses
are therefore more frequent as they don't have to line up…

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planet relative to the Earth.

Mars appears to change direction once every two years or so. Slower moving planets further out change
direction less frequently.




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P7.2 How does a telescope work?

Converging lenses are CONVEX. They get fatter towards the middle.
All lenses have a principal axis, a line which passes straight through the middle of the lens.





The focal point of a lens is where rays initially parallel to the principal axis meet. (All…

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DRAWING RAY DIAGRAMS

Most objects in space are so far away that their lights are almost parallel. We need to be able to draw
ray diagrams of the light being focused with a converging lens.

1. Draw one ray going directly through the middle of the lens. Carry this ray…

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The distance between the two lenses is equal to the sum of the two focal lengths.

What are the limitations of refracting telescopes?

Chromatic aberration different colours are focused to different points so the image is blurry.

Large lenses sag under their own weight.

Large pieces of glass are not…

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b) In a Reflecting mirror, a parabolic mirror focuses all parallel rays to one point.

This can be used as the objective of the telescope instead of a convex lens

Advantages: Reflects all colours in the same way. It is possible to build very large mirrors bigger
aperture collects more…

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P7.3 What are the objects we see in the night sky and how far
away are they?

The distance to nearby stars can be measured by parallax.

Parallax is apparent change in position of an object against a distant background.

In astronomy: The parallax angle is half the angle moved…

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All hot objects emit radiation from a continuous range of the EM spectrum. The hotter the object the
greater the luminosity overall. The hotter the object, the higher the frequency/lower the wavelength of the
radiation which is emitted the most.



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