1. Astronomy 1020-H Stellar Astronomy Spring_2015 Day-10

2. Course Announcements SW Chapter 3 & 4 … will be downloaded on Friday 2/13 during the exam. SW Chapters 13-23 are posted now Exam 1: Friday, Feb. 13 1 st set of Dark Sky observing nights: Wed. Feb. 11 & Tues. Feb. 17

4.  The gravitational interaction of three bodies leads to Lagrangian equilibrium points.  These are special orbital resonances where the object at that point orbits in lockstep.  SOHO is near L 1. CONNECTIONS 4.2

5.  Tides are a consequence of gravity.  Something closer to an object experiences a stronger gravitational pull than something else farther away.

6.  The centers of Earth and the Moon orbit like point masses.  Parts of Earth are closer to the Moon than other parts.  This produces a stretch on the Earth, called a tide.  Tides cause bulges to appear on either side.

7.  Earth’s oceans flow in response to the tidal forces.  The oceans have a tidal bulge: They are elongated in a direction that is nearly pointed at the Moon.

8.  Tides can affect the solid part of Earth, too.  A gravitational pull can stretch and deform a solid body.  Results in friction, which generates heat.  Friction also opposes the rotation of Earth, causing Earth to very gradually slow its rotation.  Days lengthen by about 0.0015 seconds every century.

9.  Because of tides, Earth is not a perfect sphere.  Earth’s leading edge creates an acceleration on the Moon in its orbit, resulting in a bigger orbit.  The lunar month increases by 0.014 seconds per century.

10.  Gravitational objects create Roche limits within which the effects from their tidal forces can destabilize other objects.  Planets, stars, and galaxies can be affected.

11.  Galaxies can be distorted with tidal tails.  Moons of planets can have great internal activity because of tides, perhaps allowing for conditions for life.

12.  The net tidal force is the difference in force on the two sides of the planet.  The Moon’s tidal forces on Earth are 2.2 times as strong as the Sun’s tidal forces on Earth, resulting in greater lunar tides than solar tides. MATH TOOLS 4.4

13. Exam - 1

14. While We Wait for Everyone

16. The Origin and Nature of Light

18. But, what is light? Newton, Remember Newton? He did more than just calculus and mechanics. In the 17th Century, Isaac Newton argued that light was composed of little particles while Christian Huygens suggested that light travels in the form of waves. In the 19 th and 20 th Century Maxwell, Young, Einstein and others were able to show that Light behaves both like a particle and a wave depending on how you observe it.

19. Thomas Young’s interference experiment

21. Maxwell – EM Field Theory Scottish physicist James Clerk Maxwell showed mathematically in the 1860s that light must be a combination of electric and magnetic fields.

22. Einstein In 1905 Einstein calculated the energy of a particle of light (photon) and proposed the photoelectric effect. E photon = hc/  = h e- photon