OCR 21st Century Physics P7

Intrinsic Brightness or luminosity is the relative quantity of radiation emitted by a celestial source (star) / how much energy the star is emitting and it depends on it's SIZE and BRIGHTNESS

Cepheid Variable Star a star with changing intrinsic brightness

Red Shift is the shift of light towards the red part of the visible light spectrum

Magnificationis the process of enlarging something only in appearance not in physical size

Parsec is a measure of distance similar in magnitude to a light-year

We measure things in the sky from two fixed points....

The celestrial equatorb and the polar star (above the north pole)

The celestrial equator is a plane extending from the earths equator

How far you move along the celestrial equator from 0h is RIGHT ASCENSION

A possitive right ascension moves to the EAST

A negative right ascension moves to the WEST

The angle between C.E and object measured is declination

A possitive declination = object can be seen in northern hemisphere

A negative declination = object can be seen in the southern hemisphere

A Solar day is the day we all know .... 24h

A Siderial day is 4min shorter ...... 23h56min

The reason for this is ......... a Solar day is basically 360 degree turn by the Earth ........ but a Siderial day takes less than 360 degrees ........ BECAUSE ....... the Earth has also moved a bit on it's travels round the sun which makes them slightly less than 360 degrees away

The moon takes ...... 25h ....... to get back to the same place in the sky