Characteristics of Stars

STAR

A star is a great ball of gas formed mostly from element hydrogen which is converted to helium through a thermonuclear reaction called fusion.

Life Cycle of Star

Life Cycle of Star

Different types of stars

Variable StarsBinariesNova

Characteristics of Stars

Characteristics of Stars

The Sun is an average star:it’s not hot or coolit’s not large or small.

We can compare stars by color, temperature, size, and brightness.

The Sun is larger than 95% of the stars.

Dwarf Star Sun Giant Star Super Giant Star

Color and Temperature

Color and Temperature

Color:Stars range in color from red, orange, yellow,

white, to blue.

Red ----------- Yellow (Sun) ----------- > Blue

Temperature:Stars range in temperature from 2000oC--50

000oC.

2 000oC ---------5 000oC (Sun)--------- > 50 000oC

Color and Temperature

Color and temperature are related.

The 2000oC stars are red in color.

The 50 000oC stars are blue in color.

Color and TemperatureColor Temp. (oC) Examples

Blue-white 12 000 Rigel, Spica

White 11 000 Vega,

White 10 500 Sirius

Yellow 6 000 Cepalla

Yellow 6 000 Sun

Orange 4 200 Arcturus

Red 3 000 Antares

Red 2 200 Betelgeuse

Light-year

A lightyear is the distance traveled by light (at the speed of 300, 000 km/s) for a period of one year.

Light travels about 9 trillion km in one year.

Another unit to express distance is the parsec, which is equivalent to 3.26 lightyears.

1 lightyear = 6 trillion km

1 parsec = 3.26 lightyears

Distance of Some Stars

Star Distance from Earth (in lightyears)

Sirius 8.5

Vega 26.5

Antares 390

Betelgeuse 587

Polaris 680

Rigel 900

Size

Compare the sizes of the stars you see at night to that of sun. Isn’t the sun much bigger than of any of them?

Brightness

Brightness

Brightness is related to the distance from the earth and the age of the star.

Classifying stars by their brightness.1st magnitude stars are the brightest6th magnitude stars are the weakest

The magnitude of a star measures brightness.

Apparent Magnitude – refers to the brightness of a star as it appears to us.

Absolute Magnitude – refers to the actual brightness given off by a star at a standard distance.

Spectrum

Spectroscope: Used to measure the chemical composition of the stars. (also temperature and direction the star is moving in relation to the Earth.)

How? Set up a spectroscope with different tubes; each gas has different spectras – light patterns.

Stars seem to twinkle, Do you see them

twinkle?Light from the distant

stars travels through various layers of the atmosphere with different densities. The layers closest to the Earth are denser than those in the upper layers because they contain dust and other particles.

Stars seem to twinkle, Do you see them

twinkle?

When light travels through a medium with varying densities, it bends. For this reason, stars are seen to flick or twinkle.

Checking Understan

ding

Questions 1. How is the color of a star related to its

temperature?The color of a star depends on its temperature,

from red and orange (cool stars) to yellow and white (hotter stars) to blue (very hot stars).

2. Explain why a cooler star could actually appear brighter than a hotter star.

A cool star, such as a red giant, could be either closer to us or much larger than a hotter star, such as a white dwarf. (Could be closer and larger)

Questions

3. How do distances of stars are expressed?

Distance of stars are expressed in

lightyears

4. What classification of color does Sun belong?

Yellow-dwarf

5. Why do we see sun as brighter?

Because it is nearer

Thank you!!!