1. Announcements Next exam is delayed one week to Monday April 7. Tentatively will cover the rest of Chapter 5 (from Kepler) and all of Chapter 6 and some of Chapter 7. Sample questions have been posted. Dark Sky Observing Night is cancelled due to clouds. First Quarter Observing Night next Monday. Starts at 8:30pm so set-up will begin at 7:30 if clear, 7:45 if cloudy

2. By using pre-discovery observations of Uranus, Bode calculates an orbit for Uranus

3. 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

4. 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

5. Eventually, an assistant of Gauss’ at the Berlin observatory, Johann Galle, locates the object: Neptune

6. 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.

7. 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

8. The birth of Stellar Astronomy

9. Prior to 1600 Stellar astronomy was just position and brightness Tycho’s Celestial Globe Johann Bayer 1603 Uranometria

10. In 1572 Tycho observed a supernova so the stars weren’t always constant

11. In 1603 Kepler observed another supernova In 1605 he publishes De Stella Nova on the new star and other celestial “events”

12. The Chinese had observed supernova long before the Europeans The Chinese observed a supernova in 1054 that becomes the Crab Nebula

13. In 1596 a Frisian, David Fabricius, notices a “nova” in Cetus In 1638 another Frisian, Johannes Holwarda observes another “nova” in the same place

14. 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

15. Ismael Boulliau proposed a star spot explanation for stellar variability

16. To aid in quantifying the variability of stars, William Herschel published a Catalogue of comparative brightness of stars

17. Two York amateur astronomers had developed the star comparison technique while studying Algol John Goodricke worked with Edward Pigott

18. The two amateurs also discover the variability of Beta Lyrae, Delta Cephei and Eta Aquilae

19. Their original explanation of an eclipsing star was right for Algol Algol System They got confused when Delta Cephei and Eta Aquilae behaved differently Beta Lyrae is also an eclipsing binary

20. If the stars change, do they also move? And how far away are they? Halley determined the Proper Motion of several stars by comparing “modern” positions to those of Ptolemy

21. Attempting to measure parallax

22. The problem required precise measurements free of atmospheric refractive effects

23. Robert Hooke had a zenith telescope built into his house to measure Gamma Draconis He encountered several problems, including a cracked lens. Although he reported a parallax angle in 1669, no one except himself believed

24. In 1725, James Bradley had a zenith telescope built to measure parallax

25. While attempting to measure parallax, he measured the Aberration of Light This was the first direct evidence for the motion of the Earth around the Sun

26. Bradley also discovered the Nutation of Earth

27. Bradley took reams of data to correct the positions of stars but died before reducing the data Fredrick Wilhelm Bessel undertook the data reductions and published them in Fundamenta Astronomiae