Page 10 - Curriculum Visions Dynamic Book

Eta Carinae, the
keyhole nebula
(catalogue number NGC 3372)
 Eta Carinae is 10,000 light-years away, and so we cannot see it in fine detail. We can only see features of about the size of our Solar System, 16 billion km across.
Because it is unstable, it is prone to sudden, violent outbursts. One eruption occurred about 150 years ago, and then Eta Carinae became one of the brightest stars in the southern sky. The explosion produced two lobes and a large, thin equatorial disk.
Eta Carinae has a mass of about 100 to 150 Suns and is one of the most massive and most luminous stars known. It is about four million times brighter than our Sun.
Measuring the heavens
To help get a perspective on the objects in the Universe,
we need a celestial measure. But our usual measurement system of kilometres will not do for such large distances. We need something more appropriate. Three units are used, in part depending on the distances involved:
Astronomical unit
The basic measurement for the Solar System is the astronomical Unit (AU). It is the average distance from the Earth to the Sun (149,597,870 km).
Light-year
The distance traveled by light through space in one Earth year is called a light-year. A light-year equals about 9,460,000,000,000 km, or 63,240 astronomical units.
Light travels through space at 300,000,000 metres per second. For measuring very long distances, therefore, the time it takes for light to cover a distance is an ideal measure.
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