03_Celestial sphere

physics.unlv.edu

03_Celestial sphere

Ch. 2

Discovering the Universe for Yourself

1


2.1 Patterns in the Night Sky

Our goals for learning:

• What does the universe look like from

Earth?

• Why do stars rise and set?

2


What does the universe look like

from Earth?

With the naked eye,

we can see more than

2,000 stars as well as

the Milky Way.

3


A constellation is a

region of the sky.

Constellations

88 constellations

fill the entire sky.

4


Often you

see this type

of diagram....

5


Consider the dome of the sky over our heads….

mixing bowl

6


Consider the dome of the sky over our heads….

The Celestial Sphere!!

inverted mixing bowl ….

7


Quiz

The brightest stars in a constellation…

A. All belong to the same star cluster.

B. All lie at about the same distance from

Earth.

C. May actually be quite far away from each

other.

8


The Celestial Sphere

Stars at different

distances all appear to

lie on the celestial

sphere.

Ecliptic is Sun’s

apparent path through

the celestial sphere.

9


Earth orbits the Sun (revolves) once every year:

• at an average distance of 1 AU ≈ 150 million km.

• with Earth’s axis tilted by 23.5º (pointing to Polaris)

• and rotating in the same direction it orbits, counterclockwise

as viewed from above the North Pole.

10


The Celestial Sphere

The 88 official

constellations

cover the celestial

sphere.

Imagining a spinning

Celestial Sphere

surrounding Earth aids

in thinking about the

position and motion of

the sky

11


The Milky Way

A band of light

making a circle

around the

celestial sphere.

What is it?

Our view into

the plane of our

galaxy.

12


The Milky Way

13


Location: Texas

Exposure: 60 min

28 mm lens

Credit:

Richard Bell

http://

www.richardbell.net/

14


The Local Sky

An object’s altitude (above horizon) and direction

(along horizon) specifies its location in your local

sky

15


The Local Sky

Zenith: The point

directly overhead

Horizon: All points

90° away from zenith

Meridian: Line

passing through zenith

and connecting N and

S points on horizon

16


Here’s the Celestial Sphere....

Celestial Sphere Rotation

Star B

2

Star A

1

2

Celestial Sphere

3

Celestial Sphere

1

4

3

Horizon

4

Celestial Sphere Rotation

Figure 2

17


Is the horizon shown a real

physical horizon, or an

imaginary plane that extends

from the observer and Earth

out to the stars?

Celestial Sphere Rotation

1

Star B

2

Star A

2

Can the observer shown see

an object located below the

horizon?

Celestial Sphere

4

3

1

Celestial Sphere

Is there a star that is in an

unobservable position?

4

3

Horizon

When a star travels from

being below the observer’s

horizon to being above the

observer’s horizon, is that star

rising or setting?

Figure 2

Celestial Sphere

Rotation

18


Lecture-Tutorial (LT):

Position (pp. 1-2)

• Work with a partner!

• Read the instructions and questions carefully.

• Discuss the concepts and your answers with one

another.

• Come to a consensus answer you both agree on.

• If you get stuck or are not sure of your answer,

ask another group.

• If you get really stuck or don’t understand what

the LT is asking, ask for help.

19


In what

Celestial Sphere Rotation

direction is the

observer

1

Star B

2

Star A

2

facing?

Celestial Sphere

3

1

Celestial Sphere

4

1. toward the South

2. toward the North

3. toward the East

4. toward the West

4

Figure 2

3

Celestial Sphere

Rotation

Horizon

20


Where would

the observer

look to see the

star indicated by

the arrow?

Celestial Sphere Rotation

1

Celestial Sphere

4

3

1

Star B

2

Star A

2

Celestial Sphere

3

Horizon

A. High in the Northeast

B. High in the Southeast

C. High in the Northwest

D. High in the Southwest

4

Figure 2

Celestial Sphere

Rotation

21


We measure the sky using angles

22


Angular Measurements

• Full circle = 360º

• 1º = 60ʹ′ (arcminutes)

• 1ʹ′ = 60ʺ″ (arcseconds)

23


Quiz

The angular size of your finger at arm’s length is

about 1°. How many arcseconds is this?

A. 60 arcseconds

B. 600 arcseconds

C. 60 × 60 = 3,600 arcseconds

24


Lecture-Tutorial (LT):

Motion (pp. 3-6)

• Work with a partner!

• Read the instructions and questions carefully.

• Discuss the concepts and your answers with one

another.

• Come to a consensus answer you both agree on.

• If you get stuck or are not sure of your answer,

ask another group.

• If you get really stuck or don’t understand what

the LT is asking, ask for help.

25

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