BC Science Connections 10

Unit 4: The formation of the universe can be explained by the big bang theory.

Topic 4.3: How has technology expanded our knowledge and understanding of

the universe?

• We have invented telescopes and other devices that extend and enhance our sense of sight.

• We know that our Milky Way galaxy is just one of many billions of galaxies in the universe.

• There are vast distances separating stars and separating galaxies.

• The properties of stars help us develop an understanding of their life cycles.

Concept 1: We have invented telescopes and other devices that extend and enhance our

sense of sight.

• Telescopes have helped us observe and study stars and planets in space.

• Telescopes can detect different forms of electromagnetic radiation like visible light and radio waves. Figure 4.17: This 26 m radio telescope is part of

the Dominion Astrophysical Observatory near

Penticton. The observatory is owned and operated

by Canada’s National Research Council.

Telescopes in Space

• Some telescopes have to be placed above Earth’s atmosphere to detect radiation (e.g., infrared and UV radiation) from space.

Figure 4.18: Only a fraction of

electromagnetic radiation from space reaches

Earth’s surface. Therefore, some telescopes

must be placed in orbit above the atmosphere

to take advantage of the wealth of information

the whole spectrum of this radiation provides.

Studying Objects in Different Wavelengths

Figure 4.19: Saturn as viewed in visible light (A),

ultraviolet (B), infrared (C), and radio waves (D).

The colours in (B), (C), and (D) are false. They

are added to highlight different features.

• Different telescopes show different information about planets based on different wavelengths.

Discussion Questions

1. How did an optical telescope change the way that we can observe and explore space?

2. How do telescopes that detect non-optical radiation contribute to our understanding of space?

Concept 2: We know that our Milky Way galaxy is just one of many billions of

galaxies in the universe.

Figure 4.20: In a dark sky, on a clear night, the Milky

Way galaxy looks like a band of white in the night

sky. The ancient Romans called it the Via Lactea,

which means “way (or road) of milk.” The term

“galaxy” also comes from an ancient word (Greek,

this time), galactos, meaning milk.

• Galaxy: a collection of many billions of stars, plus gas and dust, held together by gravity

• The Milky Way is our galaxy.

The Discovery of Galaxies

• Galileo was the first to observe the stars in the Milky Way with his telescope.

• William Herschel discovered that the Milky Way is made of a collection of stars using his telescopes.

The Shapes of Galaxies

Three galaxy shapes:

1. Elliptical galaxies are spherical to oval in shape.

• Older galaxies with few young stars

2. Spiral galaxies have a bulge in the centre and spiral arms on the sides.

• Have old stars in the centre and young stars in the spiral arms

Figure 4.21: Main types of galaxies—

an elliptical (A), spiral (B), barred

spiral (C), and irregular (D).

The Shapes of Galaxies

3. Irregular galaxies have no definite shape and no spiral arms or central core.

Figure 4.21: Main types of galaxies—

an elliptical (A), spiral (B), barred

spiral (C), and irregular (D).

Azimuth and Altitude

• https://www.youtube.com/watch?v=kcxJ3sWpvXc

Understanding the Milky Way

• Star cluster: a collection of stars held together by gravity

• Two types of star clusters:

1. Open clusters have 50–1000 stars around the Milky Way’s disk.

2. Globular clusters have 100 000–1 000 000 stars around the Milky Way’s centre.

• The Milky Way is 100 000 light-years in diameter.

• Galaxies can also differ in size, mass, colour, brightness, and speed they spin.

• These differences are determined by;

• number of stars

• amount and type of gas

• dust

• Some galaxies grow into supergiants while others remain dwarf.

What Is a light year?

• a unit of astronomical distance equivalent to the distance that light travels in one year, which is 9.4607 × 1012 km (nearly 6 trillion miles).

Reminder: The Light-Year

• Light-year: a unit of distance equal to the distance light travels in one year

• 1 light-year (ly) = 9.46 × 1012 km

Implications of the Light-Year

• It takes 8 min for light from the Sun to reach Earth, therefore we see the Sun as it was 8 min ago.

• We are looking back in time.

Understanding the Milky Way (cont’d)

• The Milky Way is a spiral galaxy.

• It has a disk-like shape.

• It has a halo of globular star clusters in the centre.

• It has lanes filled with clouds of gas and dust.

Figure 4.23: Globular clusters

form a sphere around the

centre of the Milky Way.

Galaxy Groups and Clusters

• The Milky Way is part of the Local Group made up of 50 galaxies.

• The Local Group belongs to the Virgo Supercluster, which is a large collection of galaxies.

Discussion Questions

1. Compare the three basic shapes and sizes of galaxies.

2. How did we infer our position within the Milky Way galaxy?

3. How did we infer the Milky Way is a spiral galaxy?

4. What is the Local Group?

Concept 3: There are vast distances separating stars and separating galaxies.

• AU (astronomical unit) is the unit used to measure distance between objects in space.

• Earth is 1 AU from the Sun.

Figure 4.26: Using the

AU to measure

distances in the solar

system is simpler and

more convenient than

using kilometres.

Stellar Distances

• Parallax: the apparent change in position of an object against a fixed background when it is viewed from two different lines of sight.

• Can be used to measure distances between stars in our galaxy.

Figure 4.28: Parallax

angle is the angle

measured between

two lines of sight,

divided by two.

Explaining Parallax

• Triangulation: a method that uses parallax to calculate the distance from Earth to stars.

Figure 4.29: Because

stars are distant, parallax

must be determined from

positions that are very far

apart.

https://youtu.be/Saw1Eg2iZaI

Discussion Questions

1. Describe a case where it would be convenient for astronomers to use

a) AUs, and

b) light-years.

2. Explain why kilometres are not adequate for measuring most distances in the universe.

Discussion Questions

3. The light-year is a unit of distance. Why does it seem like a unit of time?

4. How does parallax help us determine distance?

Concept 4: The properties of stars help us develop an understanding of their life cycles.

• The brightness, colour, temperature, composition, and mass of a star indicate what stage of its life cycle it is in.

Brightness of Stars

• Luminosity: the amount of energy a star gives off per second.

• It indicates how bright a star is.

• Absolute magnitude indicates how bright a star would be if it were 32.6 light-years from Earth.

Colour and Temperature of Stars

• The colour of a star indicates how hot its surface temperature is.

• A fairly hot star has a bluish colour.

• A fairly cool star has a reddish colour.

Composition of Stars

• A spectroscope is used to analyze the light given off by stars to determine their elemental composition.

• Each element has a unique spectrum.

Figure 4.31: Each element is uniquely identified by its spectrum.

Mass of Stars

• Binary star system: two stars that orbit each other.

• The mass of stars can be determined by calculating the size of the orbit of a binary star system and the time it takes for the stars to complete one orbit.

The Hertzsprung-Russell Diagram andStellar Evolution

• Hertzsprung-Russell(H-R) diagram: a graph that shows the colour and the absolute magnitude of stars.

• It shows the relationship among colour, luminosity, mass, and temperature of stars.

Figure 4.32: This simplified Hertzsprung-Russell (H-R)

diagram is based on data from thousands of stars. It shows

that there is a relationship among the colour, temperature,

luminosity, and mass of stars.

The Main Sequence

• Main sequence: narrow band of stars on the H-R diagram that runs diagonally from the upper left (bright hot stars) to the lower right corner (dim cool stars)

• Makes up about 90% of the stars that consist of bright hot stars to dim cool stars.

How Stars Evolve

• Stars will give off light for a very long time but will eventually run out of hydrogen fuel.

• When a star reaches the end of its life cycle, what it becomes will be dependent on its initial mass.

Figure 4.34: A star’s life

cycle depends on its

initial mass.

Low-Mass Stars

• Low-mass stars use up their hydrogen fuel slowly over a period of 100 billion years.

• They will eventually become white dwarfs that are faint, but hot.

Intermediate-Mass Stars

• Intermediate-mass stars use up their hydrogen fuel in about 10 billion years.

• When the hydrogen fuel is used up, the star becomes a red giant and eventually a planetary nebula and then a white dwarf.

• Our Sun is an intermediate-mass star.

High-Mass Stars

• High-mass stars use up their hydrogen fuel quickly and as a result form supergiants.

• Their core collapses violently and the outer layers explode causing a supernova.

• The stars eventually become neutron stars or black holes, depending on their initial mass.

Neutron Stars

• A star with a mass of about 10 solar masses eventually becomes a neutron star consisting of neutrons.

• The centre of the Crab Nebula contains a neutron star.

• A pulsar is a neutron star that releases pulses of radiation.

Black Holes

• A star with a mass of more than 20 solar masses eventually becomes a black hole. A black hole has no volume but does have mass.

• Cygnus X-1 is a black hole in the Milky Way

• The strong gravitational force of a black hole does not allow anything to escape it.

Summarizing the Life Cycles of Stars

Figure 4.38: Life

cycle pathways for

stars based on their

mass. (The drawings

are not to scale.)

Discussion Questions

1. List and briefly describe four properties of stars.

2. Which two properties of stars are compared in an H-R diagram?

3. What does an H-R diagram help us understand about stars?

4. Use a sketch or flowchart to outline how a star’s life cycle depends on its initial mass.

Topic 4.3 Summary: How has technology expanded our knowledge and understanding

of the universe?

• We have invented telescopes and other devices that extend and enhance our sense of sight.

• We know that our Milky Way galaxy is just one of many billions of galaxies in the universe.

• There are vast distances separating stars and separating galaxies.

• The properties of stars help us develop an understanding of their life cycles.