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Chapter

6: The mysterious universe…

6.1:

Observing the night sky…

¨ The

celestial sphere rotate above our heads, carrying with it constellations of

gleaming stars

¨ Stars

appear to wander among the constellations, these include; sun, moon and planets

¨ The celestial

model was introduced by a Greek astronomer Ptolemy in 150 AD, which was

incorrect

¨ The

apparent movement is due to the rotation of the Earth

¨ Development

of the telescope in the 16th century helped the astronomers look at

the sky

¨ It showed

many different objects in the sky, including: single or double stars, galaxies,

and clouds of gas and dusts called nebulae

¨ 3

particularly bright stars: Sirius, Procyon and Arcturus

¨ The

positions of those three stars were different compared to the rest

¨ Stars

closer to the Earth seem brighter and stars further away are dimmer.

¨ The

apparent movements of objects due to the actual movement of the observer

¨ This is

called parallax

The Horsehead Nebula in the constellation of Orion. A nebula is a cloud of dust and gas, visible as a glowing or dark shape in the sky against a background of stars.

HOW ABOUT THAT! A light-year is not a measure of time! It is a measure of distance. In one year, light travels a distance of 9 500 000 000 000 or 9.5 × 1012 kilometres. This distance is called a light-year.

A time-lapse photograph of the sky clearly shows the apparent movement of the stars.

In 150 AD, the Greek astronomer Ptolemy suggested that the stars were attached to a ‘celestial sphere’ that rotated above our heads. According to Ptolemy, the sun, the planets and the moon also orbited the Earth.

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