Announcements
•Next exam is Thursday March 24. Will
cover Chapters 6 & 7 and possibly some of
Chapter 8. Sample questions are posted.
•Dark Sky Observing Night Wednesday
night. Forecast is iffy. If we go, set-up starts
at 6:30pm. If needed, I’ll post a cancellation
notice on APSU Astronomy by 5:00pm on
the day of the observing.
•Project presentations next time!
Chaos in the Solar System
At its very inception, Newton knew that it would be impossible
to get a “closed solution” to the three body problem
The orbits of all the planets are
known to have long-term variations
The biggest problems were with the
orbits of Jupiter and Saturn
Their interactions led to
periodic variations and
what appeared to be
non-periodic changes
Lagrange and Laplace showed the
seemingly non-periodic variations
were, in fact, periodic
Lagrange
Laplace
Laplace eventually forms a theory
for why the solar system is as it is
Laplace’s
Traite de
mecanique
celeste
becomes
the
standard of
celestial
mechanics
The “missing planets” problem
a  0.4   0.3  2m 
where m  , 0,1, 2,3, 4,...
The Titus-Bode Law predicted a planet
between Mars and Jupiter. At the time, Uranus
and Neptune had not been discovered
On March 13, 1781 William
Herschel discovered Uranus
Its’ orbit
matched the
Titus-Bode Law
Baron Franz
Xaver von Zach
quickly forms
the “Celestial
Police” to hunt
down the
missing planet
between Mars
and Jupiter
Purely by chance,
Giuseppi Piazzi
discovers the
“missing planet”
on January 1,
1801. He names
it Ceres
Ceres is “lost”
for a while but
Carl Friedrich
Gauss, at the
Berlin
Observatory,
calculates an
orbit and refinds it
Within a year Heinrich Olbers
discovers another body he names
Pallas
By 1807, two more objects, Juno
and Vesta are discovered
Juno
Vesta
Olbers thought
all the asteroids
originated from
a single
“exploded”
planet but
orbital
calculations
proved
otherwise
By 1850 over a dozen objects
had been discovered
By using pre-discovery
observations of Uranus, Bode
calculates an orbit for Uranus
Urbain La Verrier uses perturbation
theory to predict another planet
The orbit of Uranus isn’t quite what it should be if you figure
the influence of Jupiter and Saturn
At the same time John Couch Adams
is making the same prediction
Adams showed his calculations to James Challis, the director
of the Cambridge Observatory. He is unimpressed but relays
the information to George Airy, the Astronomer Royal, who
makes a half-hearted attempt to find it
Eventually, an assistant of Gauss’ at
the Berlin observatory, Johann
Galle, locates the object: Neptune
The next problem to be attacked
was the orbit of Mercury
The perihelion of the orbit of Mercury was known to
precess. When all perturbations are figured in there still 43
arcseconds per century too much.
Many searched for Vulcan but it
was never found
It turns out to be Newtonian
mechanics that is error. Albert
Einstein comes up with a new
formulation of gravity: General
Relativity. It exactly describes
the orbit of Mercury
The birth of Stellar Astronomy
Prior to 1600 Stellar astronomy
was just position and brightness
Johann Bayer 1603 Uranometria
Tycho’s Celestial
Globe
In 1572
Tycho
observed a
supernova so
the stars
weren’t
always
constant
In 1603 Kepler observed another
supernova
In 1605 he publishes De
Stella Nova on the new
star and other celestial
“events”
The Chinese had observed
supernova long before the
Europeans
The Chinese observed a supernova in 1054 that
becomes the Crab Nebula
In 1596 a Frisian, David Fabricius,
notices a “nova” in Cetus
In 1638 another Frisian,
Johannes Holwarda
observes another “nova”
in the same place
By 1622 Johannes Hevelius figures
it out
He didn’t know why but he
figured out that the two
novas were actually a
single variable star
Ismael Boulliau proposed a star spot
explanation for stellar variability