Survey of the Universe Tom Burbine

Moon, Planets, and Stars All celestial objects appear to rise in the east and set in the west

Moon Besides the Sun, the Moon is the brightest object in the sky The Moon reflects light from the Sun Light areas are called highlands Dark areas are called maria (huge impact basins filled with lava)

Cycle The Moon’s changes in the sky follow a 29.5 day cycle This is why each month has approximately 30 days

Phases of the Moon day cycle

Color of lunar eclipse The Moon does not completely disappear because of the refraction of sunlight by the Earth’s atmosphere If the Earth had no atmosphere, the Moon would be completely dark during an eclipse. The red color arises because sunlight reaching the Moon must pass through the Earth’s atmosphere, where it is scattered. Shorter wavelengths are more likely to be scattered by the small particles. By the time the light has passed through the atmosphere, the longer wavelengths dominate. This resulting light reflected from the Moon we perceive as red.

Solar eclipse

Solar eclipses occur approximately every 18 months However, they recur (on average) at any given place only once every 370 years Moon's umbra moves eastward at over 1,700 km/hr Every year, there are at least two lunar eclipses. Can be viewed anywhere on the night side of the Earth

Eclipses Moon is tilted at an angle of 5 degrees to Earth’s orbit

Solar eclipse of July 22, 2009 Lasted a maximum of 6 minutes and 39 seconds off the coast of Southeast Asia

Solar eclipse of July 11, 2010 Occurred over the Southern Pacific Ocean Very remote Seen over French Polynesia, the Cook Islands, and Easter Island

Models When you have a model of how something works, you should be able to predict what will happen If observations do not fit the model, either the observations or the model is wrong The ancient astronomers wanted to predict the positions of planets in the sky

What did the ancients think That the Earth was the center of the universe (geocentric model) That the celestial sphere was rotating around the Earth However, there was two observations that caused problems with this idea –Apparent retrograde motion –Inability to detect stellar parallax

Greek model

Motion of planets Planets always appear to rise in the east and set in the west But planets usually move from west to east past the stars The exception is retrograde motion

Figure 2.6

Figure 2.7

Apparent Retrograde Motion = “backward” motion

Ptolemy’s ( AD) Model of the Universe epicycle

Occam’s Razor The principle that generally recommends selecting the hypothesis that makes the fewest new assumptions

Retrograde Motion

Any Questions?