Transcript Day 17

Announcements
•The last 1st Quarter Observing Night is tomorrow
night. Starts at 7:30pm so set-up begins at 6:45pm.
Meet here at that time. We will set-up in the Atrium
with a few Dobs outside if it is clear.
•Don’t forget the second project. Presentations are
two weeks from today.
•Exam 3 is Tuesday May 3 at 4:00pm. Will cover
Chapters 8 & 9. Sample questions are posted.
Understanding the rings of
Saturn
Galileo had observed Saturn in 1610 and
noted strange appendages
With a better telescope,
Huygens figures it out
In 1659 Christian Huygens figure out that the
strange appendages of Saturn were rings
Giovanni Cassini discovers
gaps in the rings in 1675
A smaller gap in the A ring is
named in honor of Johann
Encke for his studies of the
rings in the early 1800’s
In 1850, with one of the new
refractors, William Bond discovered
the C- ring of Saturn
His son, George Bond, though he
saw changes in the rings and
proposed they were a fluid
James Clerk Maxwell finally solved
the riddle: they are independent
particles in orbit
He published his theory in
a paper titled On the
Stability of The Motion of
Saturn’s Rings in 1859
The Search for Planet X
Percival Lowell did
calculations on the orbits of
Uranus and Neptune and
deduced there must be a 9th
planet “out there”
Lowell hired a young Clyde
Tombaugh to look for Planet X
Tombaugh used a blink
comparator to search his
images for moving objects
After several years, Tombaugh
discovered Pluto
The birth of the solar system
Laplace had proposed what became
known as the nebular hypothesis in 1796.
The theory had problems.
The biggest problem was the
angular momentum problem
Thomas Chamberlin proposed that
a passing star had pulled material
off the Sun to create the planets
Hannes Alfven in the 1960’s
proposed a magnetic fields solution
to the angular momentum problem
Theories on
the
formation of
the Moon
Prior to the Apollo days one of the
theories for our Moon was the
Capture theory
Major problem: this requires a third body to take away
some angular momentum or the Moon just drifts by
The co-accretion model was
another theory
This would make the moon’s composition identical to Earth’s.
Rocks brought back by the Apollo missions showed subtle
differences from Earth rocks thus killing this theory.
The spin-off theory was the third
theory
A rapidly rotating molten Earth flings off a blob which
forms the moon
Again, composition should be identical to Earth.
After Apollo a new theory emerged
The Giant Impact model forms a
moon with almost (but not quite)
the same composition
The Giant Impact also explains our
axial tilt
It means the Moon was once much
closer to Earth