Announcements The last scheduled observing night is next week on Wednesday. Additional nights next Tuesday and Thursday have been added. If they are clear, I expect a crowd so I need all the help I can get. We will do the first two that are clear. Don’t forget the second project. Presentations are two weeks from today. Sample questions for the last exam are posted on the class website.

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

In 1850, with one of the new refractors, William Bond discovered the C- ring of Saturn

The 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 9 th planet “out there”

Lowell hired a young Clyde Tombaugh to look for Planet X

After several years, Tombaugh discovered Pluto

The birth of the solar system Laplace had proposed what became known as the nebular hypothesis in 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

The First Astronomical Photograph John William Draper took the first successful astronomical image of the Moon in It’s debatable if his very first was “successful” but his second attempt definitely was

The first stellar spectrum was made by Henry Draper in 1872 Draper put a prism between the photographic plate and the telescope. It recorded Vega and other nearby stars. The image was black & white and uncalibrated. Henry Draper was John William Draper’s son and much of his equipment was developed by his father

William Huggins was doing similar spectrum photography at the Greenwich Observatory in England

The earliest wide-field astrophotography was by David Gill Gill’s photo ushered in a new era in astronomy

By the 1890’s E. E. Barnard was making wide-field images