Unit 1 Lesson 1: The Celestial Sphere

Unit 1 Lesson 1

The Celestial Sphere

The stars visible to us on a clear night are at very different distances from Earth, even though the sky looks "flat"

The closest star (besides the sun) is 4 light years away, but some are over 1000 times further away

The Size of the Sky

• From Earth, the sky looks like a 2D dome, not a 3D starscape

• The Celestial Sphere is the name of the imaginary dome of the sky that completely surrounds the Earth

• We can only see half of the dome at one time because the horizon blocks the rest

• Horizon: point where the earth and sky meet

Constellations

• Constellations: stars that form fixed patterns on the celestial sphere

• All stars move, but as seen from Earth, it is very slowly

  It can take 10s to 1000s of years to make a noticeable shift

• The names of most constellations are unknown in origin (no idea who named them or why)

Motions of the Sky

•  If you look at the night sky you will see the stars rise and set, just as the Sun does

• The celestial sphere rises in the east, moves across the sky, sets in the west along the celestial equator

•  Two points on the celestial sphere do not move

• Celestial Poles: points above the North an South poles that do not move in the sky

The North Star

• Polaris, the North Star, sits quite near the celestial north pole

• Polaris was not always the North Star and will eventually be replaced as the stars move across the sky

Multiple Select

Which of the following statements are correct?

• The horizon cuts the celestial sphere in half because the Earth blocks half of the sky from view

• The celestial sphere looks like a flat surface because the stars are so far away

• The stars in the sky never move, they just look like they are moving because the Earth spins

• The North Star will eventually no longer be in the right spot to look like it is sitting still in the sky

The Motions of the Sun

• Constellations that are visible change with the seasons due to the Earth’s motion around the Sun

• Every month the Sun’s glare makes certain constellations invisible to us, and this repeats year after year, called annual motions 

•  Ancient people used the movement of the stars to keep track of time 

Multiple Select

From the Edpuzzle video, how did Ancient people use the motion of the stars?

• Knowing when to plant crops

• Navigating across oceans

• Tracking the Seasons

• Measuring the Universe

The Motions of Earth

• Rotation: One complete spin around the axis (24 hours for Earth)

• Revolution: One complete trip around the star (365.25 days for Earth)

Multiple Choice

Which of the following cause the celestial sphere to move across the sky each night?

• The Rotation of the sun

• The Revolution of the Sun

• The Rotation of the Earth

• The Revolution of the Earth

Multiple Choice

Which of the following cause only certain constellations to be seen in the sky each month?

• The Rotation of the sun

• The Revolution of the Sun

• The Rotation of the Earth

• The Revolution of the Earth

The Ecliptic and the Zodiac

• If we were to mark on the celestial sphere the path that the Sun takes as it moves through the constellations we would get a line around the celestial sphere, this line is called the ecliptic

•  The region of the sky surrounding the ecliptic passes through 12 constellations called the zodiac

The Zodiac

The Zodiac

◦Aries (ram)

◦Taurus (bull)

◦Gemini (twins)

◦Cancer (crab)

◦Leo (lion)

◦Virgo (maiden)

◦Libra (scales)

◦Scorpius (scorpion)

◦Saggitarius (archer)

◦Capricornus(sea-goat)

◦Aquarius (water-bearer)

◦Pisces (fish)

Multiple Choice

What is the Ecliptic?

• An invisible line above the Equator of the Earth

• The path that the moon takes

• The path the sun takes in the sky

• The places in the sky that Eclipses can occur

Multiple Choice

What makes the Zodiac constellations important?

• They were the most important myths in Ancient Greece

• They follow the path of the sun through the sky

• They are made of the brightest stars in the sky

• They can tell the future