1. A100 Solar System The Sun Today Today’s APOD Monday, Sept. 8
Read Chapter 1 in text – History of Astronomy
Quiz Today (essential facts and scientific notation)
Rooftop Session Sept. 10, 9 PM
1st Homework due Friday (get it on Oncourse)
Today’s APOD
The Sun Today

2. First Quiz Bubble and write your name on the Scantron form
You may consult with your neighbors
No books, notes, papers, internet, cell phones

3. What can we see in the night sky?
With the naked eye, we can see more than 2,000 stars, as well as 5 planets, the Moon, comets, meteors, the Milky Way, and a few other special objects
The Milky Way is a band of light that makes a circle around the celestial sphere

4. Orion rising The night sky is familiar, but few people look
closely at (or think about) the complex phenomena
we observe in sky.

5. The Sky! Sky chart for 9 PM TONIGHT
North
South
The Sky!
Sky chart for
9 PM TONIGHT
The brightness of a star is shown by the size of its dot
Jupiter & the Moon in Sagittarius

6. Jupiter & the Moon in Sagittarius
Just look south… Jupiter is the brightest object in the southern sky
Sept 8
Sept 9

7. Check out the just south of west, just after sunset
See Mercury, Venus, and Mars
You will need to be able to see low on the horizon to the west southwest

8. Constellations
A constellation is a region of the sky
Constellation regions are irregular in shape

9. Do the Stars in a constellation belong together?
NO!
The stars in a constellation are not all at the same distance from the Sun
They do not form a real group in space

10. The Big Dipper is part of the constellation Ursa Major
The stars of the Big Dipper are not all at the same distance from the Sun

11. The Constellations
The 88 official (defined by the International Astronomical Union) constellations cover the celestial sphere

12. The Celestial Sphere
The stars all appear to lie on a large sphere surrounding the Earth (the celestial sphere)
Really, the stars are all at different distances

13. Angular Measurements Full circle = 360º 1º = 60 (arcminutes)
1 = 60 (arcseconds)

14. We measure the sky using angles

15. Measure the Angular Size
Image taken by the Galileo spacecraft (Jupiter, ) during its lunar fly-by in December, 1992
The dark areas are lava rock filled impact basins (mare)
Tycho impact basin
The “real” Moon is ½ degree across

16. Angular Size
distance
angular size
physical size
An object’s angular size appears smaller if it is farther away
The angular size of Mars changes depending on where Earth and Mars are in their orbits

17. The Local Sky
An object’s altitude (above horizon) and direction (along horizon) gives its location in your local sky

18. Definitions: 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

19. Our view from Earth: A circumpolar star never sets Celestial equator
Stars near the north celestial pole are circumpolar and never set.
All other stars (and Sun, Moon, planets) rise in east and set in west.
A circumpolar star never sets
Celestial equator
This star never rises in Indiana

20. Why do stars rise and set?
Stars in the northern sky circle the northern celestial pole (in the southern hemisphere stars circle the southern celestial pole)

21. The Earth spins under Polaris
(Polaris is NOT
the brightest
star in the sky!)

22. North
South
Big Dipper’s on its side in the northwestern sky
Finding Polaris
Find an open area away from nearby lights where you have a good view of the sky
Find the Big Dipper in the northwestern sky
Sky chart for 9 PM TONIGHT

23. Finding Polaris To find Polaris: find the Big Dipper follow to Polaris
the Big Dipper is ALWAYS up in Indiana!
Finding Polaris

24. Altitude of the celestial pole = your latitude

25. Why do the constellations we see depend on latitude and time of year?
They depend on latitude because your position on Earth determines which constellations remain below the horizon.
They depend on time of year because Earth’s orbit changes the apparent location of the Sun among the stars.

26. The sky changes as Earth orbits the Sun
As the Earth orbits the Sun, different constellations are visible at night
At midnight, the stars on our meridian are opposite the Sun in the sky

27. Where on the Earth is it possible to see the most stars through the year?
a) From the north pole
b) From latitude 23.5 degrees
c) From the equator
d) anywhere, since latitude makes no difference.

28. Precession!
Over time, the direction of the Earth’s rotation axis drifts around a circle.
At different times, different stars (other than Polaris) are close to the pole
The location of the celestial pole traces out a circle in the sky every 26,000 years

29. Vocabulary Review Constellation Ecliptic Equator Celestial sphere
Latitude
Longitude
Meridian
Zenith
Horizon
Altitude
North and south celestial poles

30. One question I’ve always had about astronomy is…

31. Dates to Remember ASSIGNMENTS this week Read Chapter 1, History of…
Kirkwood Obs. open Weds.
Rooftop Sky Viewing Weds.
1st HW due Friday