Stars Expectations: D2.3, D2.5,

How do Stars Differ? Size Mass Brightness (Luminosity) Composition Temperature Colour

Different Stars

More Massive Stars

Luminosity Luminosity is the measure of the total amount of energy a star radiates per second. Compared to our Sun, some stars are 30 000 times more luminous and others are 10 000 times less luminous.

Measuring a Star’s Temperature Think of an element on an electric stove. While it’s cold (room temp), the metal rings are black. Turn on the element and as it warms up, it starts to shine, first in a red colour, then an orange colour, and finally at its hottest temperature, a blue colour.

Likewise “cooler” stars (3000°C) are red in colour; our Sun at 6000°C is yellow in colour; and the hottest starts (in the 20 000°C – 35 000°C range) are blue in colour.

Composition of a Star Every element on the periodic table will produce its own colour- and if observed with a spectroscope, its own specific spectral pattern. If heated hot enough, the element will produce very narrow bands of various colours of light. This is called an emmision spectrum. If the element is made into a vapour and white light is passed through it, some colours of light are absorbed by the gas, producing a pattern of narrow black lines. This is called an absorption spectrum.

Look at the two figures below Look at the two figures below. In Figure 1 you can see the emission lines of hydrogen. Figure 2 shows the absorption spectrum. It is the exact opposite of the emission spectrum! Figure 1 - Absorption spectrum of Hydrogen Figure 2 - Emission spectrum of Hydrogen

Life Cycle of Stars Nebula: birthplace of a star, made of gas and dust

Nebula

The life of a star is determined by its mass The life of a star is determined by its mass. The more massive the star, the faster its rate of nuclear fusion and therefore a shorter life.

Hertzsprung-Russell Diagram

Class Work Worksheet Read p. 370-373 Read p. 375-382 Answer page 373 #1-3, 5, 7-9 Read p. 375-382 Answer page 382 #3-4, 6, 7, 9