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Finding the North

Star

Celestial Sphere vs. Horizon Demo

Position Lecture Tutorial (pg. 1-2) •  Work with a partner or two •  Read the instructions and questions carefully. •  Discuss the concepts and your answers with one

another. Take time to understand it now!!!! •  Come to a consensus answer you both agree on

and write complete thoughts in your workbook. •  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 Lecture Tutorial is asking, ask me for help.

What direction would you have to look to see Star A when it is highest in the sky?

A.  Toward the north B.  Toward the south C.  Toward the east D.  Toward the west E.  Directly Overhead

Imagining a spinning Celestial Sphere

surrounding Earth still aids

in thinking about the

position and motion of the

sky

Looking at the Night Sky

How to find your way around: •  Position -> where is that object? •  Distance -> how much space between these

two things? •  Motion -> where will that object be later

tonight?

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Using Angles Distances on the sky are measured in degrees, arc-minutes, and arc-seconds

•  1 degree = 60 arc-min

•  1 arc-min = 60 arc-sec

•  Width of index finger = 1º

•  Width of three fingers = 5º

•  Width of entire hand = 10º

Earth’s rotation

causes the Sun, Planets,

Moon and stars to

appear to move when viewed from

Earth

Rising and Setting Stars •  The Earth’s eastward rotation

causes stars to appear to move westward.

•  Stars near the North Celestial Pole move in small circles, and are called circumpolar

•  Stars far from the pole move in long arcs

Which of the stars will set on the western horizon?

A.  Both Star A and Star B

B.  Neither Star A nor Star B

C.  Only Star A D.  Only Star B

Tutorial: Motion – p. 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 Lecture Tutorial is asking, ask me for help.

What can you see?

If you go outside tonight, you’ll see a particular set of constellations. What factors do you think determine what you’ll see in your sky?

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Why can’t we see the same constellations all year round?

The Sun is in front of different constellations!

Zodiac - The 13 Zodiacal constellations that our Sun covers-up (blocks) in the course of

one year (used to be only 12)

•  Aquarius •  Pisces •  Aries •  Taurus •  Gemini •  Cancer

•  Leo •  Libra •  Virgo •  Scorpius •  Ophiuchus •  Sagittarius •  Capricornus

The Zodiacal Constellations that our Sun covers-up (blocks) in the course of one year (only 12 are shown

here)

North Star

365 days

1 day Aries

Pisces

Taurus

Gemini Cancer Leo

Virgo Libra

Scorpius

Sagittarius

Capricornus Aquarius

Figure 1

Which

constellation is the Sun in front of for

the situation shown? Pisces

Aries

Taurus

Gemini

Cancer

Figure 2 – What it would look like if you were the observer in Figure 1

South

North Star

365 days

1 day Aries

Pisces

Taurus

Gemini

Cancer Leo Virgo

Libra

Scorpius

Sagittarius

Capricornus

Aquarius

Figure 1

Lecture-Tutorial: Seasonal Stars (p. 7-9)

•  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 all 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

Lecture Tutorial is asking, ask me for help.

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Astronomy is BIG! Units of Length

•  British – Miles, feet, inches

•  Metric – Based on the meter

•  Astronomical Unit (AU) – Based on the Earth-Sun distance

•  Light-Years – Based on the speed of light

Metric System

•  Everything is based on the meter (m) – 1 kilometer (km) = 1000 m = 103 m – 1 centimeter (cm) = 0.01 m = 10-2 m – 1 millimeter (mm) = 0.001 m = 10-3 m – 1 nanometer (nm) = 0.000000001 m = 10-9 m

•  Good estimates: – 1 meter is about 3 feet – 1 inch is about 2.5 centimeters – 5 miles is about 8 kilometers

The Astronomical Unit (AU) 1 AU = 9.3 x 107 miles (93 million miles)

The Light-Year (ly) 1 light year = 5.8 x 1012 miles (5.8 trillion miles!):

The distance a beam of light can travel in 1 year.

365 days later...

5.8 trillion miles

Where is the Sun at noon today?

east west south

zenith

here or there?

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How can we describe the motion of the sun in the sky?

east west south

zenith meridian

PM or post meridian

AM or ante meridian

LUNCH!!

Where is the Sun throughout the year?

east west south

zenith

Dec 21 Winter Solstice

June 21 Summer Solstice

Mar 21 (Vernal)

and Sept 21

(Autumnal) Equinox

The Reason for the Seasons Hypothesis: Seasons are caused by the Earth moving closer to

or farther from the Sun.

1.  Data: When things are closer to the a light source (like the Sun) they get hotter.

2.  Data: Northern hemisphere has summer in June, July and August; Southern hemisphere has summer in December, January and February

3.  Data: Earth’s distance from the Sun hardly changes in the course of a year. (about 1%)

–  Earth is closest to the Sun on January 4

Can #2 be true if our hypothesis is correct?

No!

•  Then everyone should have summer at the same time Something else must be going on

Reason for the Seasons

•  The seasons are caused by the tilt of the Earth’s axis

•  In Summer, the Sun’s rays are more direct and the days are longer

•  In Winter, the Sun’s rays are less direct and the days are shorter

The Seasons do NOT occur because the Earth gets closer or farther from the Sun

Reason #1: More or Less Intense Sunlight

•  A direct beam of light shines on a smaller area than a glancing beam.

•  So a direct beam is more intense

Summer Winter

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Reason #2: Longer or Shorter Days

Winter Solstice

Fall/Spring Equinoxes

Summer Solstice

Altitude of the Sun Animation:

As we watch the animation, pay attention to •  Where the sun rises and sets •  Altitude of the sun at mid-day

Also, watch how the shadow changes during a day and over the course of the year.

Lecture-Tutorial: Seasons (p. 93-98)

•  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 all 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 Lecture Tutorial is asking, ask me for help.