Chapter 1 Discovering the Night Sky

A 24 Hour picture at the South Pole. What’s different?

What do you think?

• Are constellations just mythic figures in the sky?

• What causes the seasons?

• How many zodiac constellations are there?

• When, if ever, is the Moon visible during the daytime?

• Does the Moon have a dark side that we never see from Earth?

THE SCALES OF THE UNIVERSE

The range of objects we study are from the extremely small subatomic particles, to objects which are gigantic, such as a galaxy or the size of the known universe itself.

Each division up the line indicates an increase in size by 100,000.

Size of the universe video

Constellations make locating stars easy

Constellations and Asterisms • Constellations are

areas

in the daytime and nighttime sky.

• They originated from myths, but today they help star gazers to organize and describe what they see • Asterisms are the mythical figures in the sky.

• The asterism Orion is in the Constellation Orion

Use the

Big Dipper

in the northern sky as a way to find other groups of stars

Use the

winter triangle

to find southern constellations during winter evenings

Use the

Summer Triangle

to find southern constellations during summer evenings

Angular distances between stars in the sky are measured in degrees

Angular distances between stars in the sky are measured in degrees

Night time Sky • The sky in and around Lisle isn’t very dark • It seems a lot darker than Chicago, and it is, but it is still not very dark.

• This is a map that will help to compare the light pollution at different places in the U.S.

• Dark Sky finder

Using Angular Size to Solve a Problem • How does the Angular size of the Moon on the horizon compare to the angular size of the moon when it is high in the sky?

Using Angular Size to Solve a Problem • How does the Angular size of the Moon on the horizon compare to the angular size of the moon when it is high in the sky?

• How does the Angular size of the Sun on the horizon compare to the angular size of the Sun when it is high in the sky?

• How does the Angular size of the Sun compare to the angular size of the Moon?

Solar Eclipse

Solar Elclipse

Hyperlink to Sidereal vs . synodic month

Solar Eclipse Annular Eclipse -moon within sun Partial Eclipse Total Eclipse -totality

An anular eclipse is when a small ring of the Sun is visible

Here is some cool information on Lunar Eclipses http://www.mreclipse.com/Special/ LEprimer.html

Eclipses occur only when the Moon crosses the ecliptic during the new or full phase

Power of the Mayans The serpent comes only on the days of the equinoxes Video of serpent

• • •

The Greek philosopher Aristotle (died 324 B.C.) proposed that the heavens were literally composed of 55 concentric, crystalline spheres to which the celestial objects were attached and which rotated at different velocities with the Earth at the center. The following figure illustrates the ordering of the spheres to which the Sun, Moon, and visible planets were attached. With the help of the Catholic Church, this view predominated until 1611 when Galileo was able to show otherwise.

The church believed that the holy scripture had clearly indicated that the Earth is at the center of the Universe, anything else would be heresy. Galileo was put under house arrest and spent the rest of his life there. He was lucky.

An imaginary

Celestial Sphere

surrounding Earth aids in navigating the sky

A neat trick for when you become a Sailor • Polaris is the North Star • It is directly above the North Pole on the Celestial Sphere • The North Star is always the same degrees of declination as you position in latitude • This is one of the modes of maritime navigation before GPS (Beware of technology it can make you stupid/helpless if you are not careful!)

What we see in the Sky • Here is a simulation that will help to visualize our perspective on the celestial sphere

Earth’s rotation causes the Sun and stars to appear to move

Motion of Stars at the North Pole

Motion of Stars at the Equator

What about the Sun? It seems to move across the celestial sphere on a path called the

ecliptic

.

Signs of the zodiac • Before the family guy, people used to spend much more time gazing at the night sky.

• Over periods of 1000s of years, human kind began to share stories about the night sky and spread mythologies about how the stars “got into the sky” • Humans had “seen” figures in the sky and named them.

• The most important of those are the asterisms that make up the asterisms of the zodiac

Astronomy and Astrology don’t always agree Constellation Astrology Date Aries March 21 - April 20 Taurus Gemini April 21 - May 21 May 22 - June 21 Cancer Leo Virgo Libra Scorpio Ophiuchus Sagittarius June 22 - July 22 July 23 - August 21 August 22 - September 23 September 24 - October 23 October 24 - November 22 Not Included November 23 - December 22 Capricorn Aquarius Pisces December 23 - January 20 January 21 - February 19 February 20 to March 20 True Date April 19 - May 13 May 14 - June 19 June 20 - July 20 July 21 - August 9 August 10 - September 15 September 16 - October 30 October 31 - November 22 November 23 - November 29 November 30 - December 17 December 18 - January 18 January 19 - February 15 February 16 - March 11 March 12 - April 18 Notice how the Sun spends more time in Ophiuchus (

OH-fee-U-kus)

than in Scorpio yet Ophiuchus is not included in the Astrology

Summer solstice Winter solstice Equinox position

The Sun rises at different points along the horizon at different times of the year and also peaks at different heights.

Position of the “noon-time” Sun when photographed every two weeks over a year

The “altitude” of the Sun impacts how much energy is received on Earth resulting in

seasons

.

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

Because of the Earth’s slightly oval (elliptical) orbit, its distance from the Sun changes throughout the year. We (in the northern hemisphere) are actually closer during our winter.

In other words ...

• The Earth’s rotation on its axis determines the length of the day • The Earth’s orbit around the Sun ( revolution ) determines the length of the year • The Earth’s tilt with respect to the ecliptic causes the seasons.

One common misconception is that the Moon is only visible at night. However, the time of day in which the Moon is in our sky varies depending on its phase. This picture clearly displays the Moon, visible during the day.

The changing phases of the Moon originally inspired the concept of the

month

What did you think?

• • • •

Are constellations just mythic figures in the sky?

A constellation is an entire region of the celestial sphere and all that stars in it.

What causes the seasons?

The tilt of Earth’s rotational axis causes the seasons.

How many zodiac constellations are there?

There are 13 zodiac constellations, the “unknown one is Ophiuchus.

When, if ever, is the Moon visible during the daytime?

The Moon is visible during the day for half of the lunar cycle of phases.

Self-Check 1. Describe the nature and value of constellations and asterysms.

2. Define the elements of the celestial sphere.

3. Describe how the appearance of the sky changes over time because of the motion on Earth.

3. Define two solstices and two equinoxes; explain the orientation of the ecliptic on the celestial sphere and how it produces seasons on the Earth.

Self-Check 5. Explain by drawing a diagram showing how lunar phases are controlled by the relative positions of the Sun and the Moon.

6. Explain when and why solar and lunar eclipses occur and why there are not such eclipses every month.

7. Be able to describe the parts of an eclipse.