1. Discovering the night sky

2. Patterns of Stars
When you stargaze, without too much light pollution, the unaided human eye can only detect about 6000stars over the entire sky.
At any one time, you can see roughly 2000 stars (those above the horizon – the boundary between Earth and sky)
Smoggy or light polluted areas – only a tenth of that

3. These patterns of stars, formed by the brightest of the stars, are formally called asterisms.
You are more familiar with the common names, such as the Big Dipper or Orion. These are informally called constellations and have names derived from ancient legends.

4. Cancer
A crab that was sent to pinch and distract Hercules while he was fighting the Hydra

5. Leo Hera ordered creation of lion
Hercules strangled the lion after it killed people and cattle

6. Orion Orion was a great hunter
Feel in love with Artemis – moon goddess
Killed by Scorpius – and placed in the night sky opposite so he can’t see Scorpius

7. Scorpius
Scorpion sent by Gala to battle Orion – she felt like he was killing too many animals

8. Ursa Major
Arcas – illegitimate son of Zeus. Zeus turned him into a bear after he tried to kill his mother

9. Ursa Minor
Callisto – who was turned into a bear by Hera

10. Polaris (the North star)
Found from the “pointer stars” on the Big Dipper, and on the “handle” of the Little Dipper, it is located right over the North Pole.
Polaris is considered a “moderately bright” star, but is not even among the 20 brightest.
But face Polaris, and you are facing north.

11. Brightest Star in the Sky
The brightest star in the night sky is Sirius.
Locate the belt of Orion, and follow a straight mental line to the left.
Hand out table of brightest stars

12. The Celestial Sphere
Astronomers have created a “sky map” called the celestial sphere, and applied a coordinate system to it.
This system is analogous to north/south and east/west of latitude and longitude
If you know a star’s celestial coordinates, you can locate it quickly.

13. Constellations
The celestial sphere is divided into 88 constellations of different sizes and shapes.
The boundaries of constellations are straight lines that meet at right angles.
Hand out list of constellations

14. So while asterisms are called constellations in normal conversations, astronomers use the word constellation to describe an entire area of the sky and all the object in it.

15. Celestial Sphere, cont…
Stars only seem fixed on the sphere because of their remoteness – in reality, they are at widely varying distances from Earth, and they DO move relative to one another
But they are all more than 25 trillion miles from us; so although they may change, the changes over the course of a human lifetime are insignificant
Therefore, the celestial sphere is a great tool for navigating the heavens

16. So declination (dec) is equivalent to latitude,
and right ascension
(ra) is like longitude.

17. Earth’s rotation rotation – Earth on its axis; creates day and night
diurnal motion – daily motion of celestial bodies (can see through time exposure)
revolution – motion of any astronomical object around another astronomical object
sidereal period – length of time it takes for any cycle of motion (for Earth around the sun it’s 365 ¼ days)

18.
Circumpolar star trails – long exposure aimed at the South Pole – any stars that pass between the pole and the ground are circumpolar – they never go below the horizon.

19. Stars at celestial equator
Stars at celestial equator

20. Seasons
Both the tilt of the Earth’s axis and the revolution around the Sun result in the Earth having seasons
The Earth’s rotation axis tilt is exactly 23½◦

21. So what differences do you see at equinoxes and solstices?
Sun is lowest in the northern sky in winter solstice – as the Sun moves north, the amount of daylight increases
When the sun reaches the summer solstice, it is highest in the northern sky and is above the horizon for the most number of hours

22. At latitudes above 66½° north or below 66½° south, the Sun does not rise at all during parts of fall or winter – during spring and summer, they have continuous sunlight for weeks or months.

23. Eclipses and Phases
lunar eclipse – when the Moon passes through the Earth's shadow
Moon often darkens to deep red in color
Only happens when Sun, Earth, and Moon are in a straight line at a full Moon
solar eclipse – when the Moon’s shadow moves across the Earth’s surface
Broad daylight turns into
twilight
Moon moves in front of
the Sun

24. Conditions for Eclipses
Although it seems like they should occur every new and full moon, they happen much less
The moon’s orbit is tilted 5° from the ecliptic, so the full and new moons often occur when the Moon is above or below the Earth’s orbit
Moon crosses the ecliptic at lines of nodes
Happens so rarely – eclipses are about 2-5 every year, no more than 7 combined
handout

25. Three types of Lunar Eclipses
Earth’s shadow has two distinct parts
umbra – part of the shadow where all light is blocked by the Earth
penumbra – Earth blocks only some of the sunlight

26. If you were in the umbra looking at Earth, you couldn’t see the Sun.
If you were in the penumbra looking at Earth, you would see a crescent Sun.
How the Moon travels through Earth’s shadow, results in the type of lunar eclipse formed.

28. Why red?
A small amount of sunlight passing through Earth’s atmosphere is bent into the umbra. The light deflected is primarily in the red and orange end of the spectrum, and so the darkened moon will glow in that color.

29. Three types of Solar Eclipses
The moon’s shadow also has an umbra and a penumbra region. So depending on where the Earth is in that shadow, that is the type of eclipse formed.