The Crab Nebula is the remnant of a supernova explosion that was seen on Earth in 1054 AD. It is 6000 light years from Earth. At the center of the bright nebula is a rapidly spinning neutron star, or pulsar that emits pulses of radiation 30 times a second. Here are pictures of the Crab at x- ray (Chandra), optical (Palomar), infrared (Keck), and radio (VLA) wavelengths."

Ancient astronomers were aware of the motions of the sun, the moon and the stars. They were also aware of the motion of five other bodies in the sky – Mercury, Venus, Mars, Jupiter and Saturn but could not easily explain their motion in the same Earth-centric terms. Motion of the Planets

The Motions of the Planets The planets change places in the sky from night to night just like the Moon and the Sun – “planetes” is Greek for “wanderer” They generally move across the sky from east to west as the sun does (called prograde motion), but speed up and slow down, sometimes go backward or in loops, known as retrograde motion b3MDMTE- ?p=retrograde+motion&vid=f191a93d46c0183e3489da4658ed5c33&l=1%3A15&turl=http%3A%2F%2Fts1.mm.bing.net%2Fth%3Fid%3DV %26pid%3D15.1&rurl=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DuasjeDD1Q98&tit=Retrograde+Motion&c=10&sigr=11akbmrgt&ag e=0&fr=mcafee&tt=b

The Motions of the Planets The closer the planet is to the Earth, the brighter is appears – why? –Mars, Jupiter and Saturn are ALWAYS brighter during retrograde portions of orbits

Figure 1.1

Planetary Motions Why do planet’s have a retrograde motion? Early scientists used the “epicycle” to describe the movement of the planet as it orbited the earth – an idea known as the Geocentric Model, constructed in part by Ptolemy (Greek, 140 AD) and based on views by Aristotle (Greek, 350 BC)

Figure 1.2

Planetary Motions By adjusting the relative sizes of the epicycle and deferent, the planet’s speed on the epicycle and the epicycle’s speed on the deferent, this model was brought into fairly good agreement with what they saw and able to fairly well predict the positions of the known planets to the accuracy of the time. With increasing number & quality of observations, corrections were needed and Earth could no longer be the center to keep it all working.

Figure youtube.co m/watch?v =EpSy0Lk m3zM

Motions of the Planets Simplify!!!! Aristarchus (Greek, 250 BC) was the first known astronomer to suggest that the Sun was at the center with planets orbiting it, and that Earth rotates once on its axis per day Why would it be so hard to convince people that the Earth was moving around the Sun?

Motions of the Planets The Geocentric model survived until work by Copernicus (Polish, 1520) showed that the Earth was not at the center Copernican Revolution

Motions of the Planets Copernicus’ Heliocentric model –explained the observed daily and seasonal changes, and –accounted for the retrograde motion and brightness variations (catching up to Mars made the appearance of loops and we were closer so it would be brighter)

Motions of the Planets Not widely accepted during his lifetime; delayed publication of his books, possibly for fear of the Roman Catholic Church –Violated Church doctrine by relegating Earth to a noncentral and undistinguished place within the solar system

On The Revolution of the Celestial Spheres Copernicus’s book caused an amazing amount of controversy. Martin Luther attacked his book by saying that Copernicus was "the fool who would overthrow the whole science of astronomy." Religious leaders attacked the heliocentric system by saying that they were contrary to scriptural revelations. The publisher of his book even inserted an anonymous apologetic note the readers of his book implying that his ideas were far fetched. Since the heliocentric cosmology was contrary to church ideas, advocating Copernicus’s ideas was punishable as heresy so the scientific community at that time was extremely reluctant to have anything to do with it. Philosopher Giordano Bruno committed this "crime" and was burned at the stake.

Figure 1.5