Announcements Monday January 23

1
AnnouncementsMonday January 23

• First online homework assignment
• Was due Sunday at midnight, but
• Did not count (practice only)
• Need help?
• Go to Astronomy Tutorial room 665 VAN
• PRS units
• Do not purchase (yet) !
• Will be available at bookstores in early February

2
Homework

• Assignment 2
• on available now, until midnight Sunday
• Due January 30 (Sunday) at midnight
• Grading scheme (homework 2 onward)
• Each homework counts 20 pts total
• request solution button disabled
• 3 penalty wrong answer per part
• 2 bonus for not using hint per part
• Some questions randomized (question changes with
  individual student)
• Must be completed by deadline (no credit after)

• Examples of grading for homework with 10 parts
  (20 pts total)
• All correct answers, no hints used 20pts
  (0.02 x10) 20 pts 24 pts
• 6 correct answers, no hints 4 with 1 hint 1.12
  x 14pts 0.97 x 6pts 21 pts
• All 10 parts used hints, 3 hints per part 0.91 x
  20pts 18pts
• 7 correct answers, total of 5 hints per part
  0.85 x 14pts 12pts

3
Check your student ID!

• Login
• Click Change your Student ID here
• Make sure you ID is 8 digits, including two
  leading zeros

4
Checking homework scoringSee your total score
click on submit problem button at the end of
the assignment
5
Sky Patrol Looking South at dusk during the next
week
6
Orion (The Hunter) Constellation
Betelgeuse
Rigel
7
Southern view 9pm tonight (Jan 23 2006) Dominated
by Orion (The Hunter)
8
The scale of the solar system

• If the Sun is the size of a basketball
• Size, distance of Earth?
• Earth is the size of a BB, 15 meters (50) away.
• How big is solar system?
• Neptune is a golf ball about 1 mile away (City
  Park)
• Distance to nearest star?
• Nearest star is 6,000 miles away! (Egypt)

Orbit of Neptune
SunBasketball
9
Review

• How big is Earth compared to our solar system?
• The distances between planets are huge compared
  to their sizeson a scale of 1-to-10 billion,
  Earth is the size of a BB and the Sun is 15
  meters away
• How far away are the stars?
• On the same scale, the stars are thousands of km
  away
• How big is the Milky Way galaxy?
• It would take more than 3,000 years to count the
  stars in the Milky Way Galaxy at a rate of one
  per second, and they are spread across 100,000
  light-years

10

• How big is the universe?
• The observable universe is 14 billion light-years
  in radius and contains over 100 billion galaxies
  with a total number of stars comparable to the
  number of grains of sand on all of Earths
  beaches
• How do our lifetimes compare to the age of the
  universe?
• On a cosmic calendar that compresses the history
  of the Universe into one year, human civilization
  is just a few seconds old, and a human lifetime
  is a fraction of a second

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1.3 Spaceship Earth
Key questions

• How is Earth moving in our solar system?
• How is our solar system moving in the Galaxy?
• How do galaxies move within the Universe?
• Are we ever sitting still?

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How is Earth moving in our solar system?

• Contrary to our perception, we are not sitting
  still.
• We are moving with the Earth in several ways, and
  at surprisingly fast speeds

The Earth rotates around its axis once every day.
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Earth orbits the Sun (revolves) once every year

• at an average distance of 1 AU 150 million km.
• with Earths axis tilted by 23.5º (pointing to
  Polaris)
• and rotating in the same direction it orbits,
  counter-clockwise as viewed from above the North
  Pole.

14
Our Sun moves randomly relative to the other
stars in the local Solar neighborhood

• typical relative speeds of more than 70,000
  km/hr
• but stars are so far away that we cannot easily
  notice their motion

And orbits the galaxy every 230 million years.

15
More detailed study of the Milky Ways rotation
reveals one of the greatest mysteries in
astronomy
Most of Milky Ways light comes from disk and
bulge
. but most of the mass is in its halo
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How do galaxies move within the universe?
Galaxies are carried along with the expansion of
the Universe. But how did Hubble figure out that
the universe is expanding?
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Hubble discovered that

• All galaxies outside our Local Group are moving
  away from us.
• The more distant the galaxy, the faster it is
  racing away.

Conclusion We live in an expanding universe.
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Are we ever sitting still?
Earth rotates on axis gt 1,000 km/hr
Earth orbits Sun gt 100,000 km/hr
Solar system moves among stars 70,000 km/hr
Milky Way rotates 800,000 km/hr
Milky Way moves in Local Group
Universe expands
19
Review

• How is Earth moving in our solar system?
• It rotates on its axis once a day and orbit the
  Sun at a distance of 1 A.U. 150 million km
• How is our solar system moving in the Milky Way
  galaxy?
• Stars in the Local Neighborhood move randomly
  relative to one another and orbit the center of
  the Milky Way in about 230 million years

20

• How do galaxies move within the universe?
• All galaxies beyond the Local Group are moving
  away from us with expansion of the Universe the
  more distant they are, the faster theyre moving
• Are we ever sitting still?
• No!

21
Q The recently launched spacecraft New Horizons
is traveling so fast (V 30,000 kph 20,000 mph)
that it reached the Moons orbit in 9 hours
(Apollo took 3 days). At that speed, how long
would it take to reach the nearest star (distance
3 ly)?

• 10 yrs
• 100 yrs
• 1,000 yrs
• 10,000 yrs
• 100,000 yrs

D 3 l.y. 31013 km V 30,000 km/hr 3108
km/yr T D/V 31013 km / 3108 km/yr T 105
yr 100,000 yr