Please press “1” to test your transmitter. :10 0 of

From Los Angeles, CA (longitude = 118 o West; latitude = +34 o [North]), you can see the Celestial North Pole … :10 0 of Not at all o above the northern horizon o above the southern horizon o above the northern horizon o above the southern horizon.

Example: New York City: l ≈ Horizon North Celestial North Pole South Celestial Equator The Celestial South Pole is not visible from the northern hemisphere. Horizon

From Los Angeles, CA (longitude = 118 o West; latitude = +34 o [North]), looking north, you will see stars … :10 0 of Move across the sky from right to left. 2.Move across the sky from left to right. 3.Circle around the Celestial North Pole counterclockwise. 4.Circle around the Celestial North Pole clockwise.. 5.Rising and moving up across the sky.

Apparent Motion of the Celestial Sphere

Apparent Motion of the Celestial Sphere II

Which statement about Polaris is true? :10 0 of The Earth’s North Pole will always (even many thousand years from now) point towards Polaris. 2.Polaris is the brightest star in the night sky. 3.Polaris is visible from everywhere around the world. 4.All of the above. 5.None of the above.

Precession (I) Gravity is pulling on a slanted top. => Wobbling around the vertical. The Sun’s gravity is doing the same to the Earth. The resulting “wobbling” of the Earth’s axis of rotation around the vertical to the Ecliptic takes about 26,000 years and is called precession.

Precession As a result of precession, the celestial north pole follows a circular pattern on the sky, once every 26,000 years. It will be closest to Polaris ~ A.D ~ 12,000 years from now, it will be close to Vega in the constellation Lyra. There is nothing peculiar about Polaris at all (neither particularly bright nor nearby etc.)

The moon’s orbit around the Earth … :10 0 of Lies exactly in the plane of the ecliptic. 2.Is inclined by about 23.5 o against the ecliptic. 3.Is inclined by about 5 o against the ecliptic. 4.Lies almost exactly in the plane of the Earth’s equator. 5.Is inclined by about 5 o against the plane of the Earth’s equator.

Conditions for Eclipses (I) The Moon’s orbit is inclined against the ecliptic by ~ 5 0. A solar eclipse can only occur if the Moon passes a node near New Moon. A lunar eclipse can only occur if the Moon passes a node near Full Moon.

Conditions for Eclipses (II) Eclipses occur in a cyclic pattern. → Saros cycle: 18 years, 11 days, 8 hours

Kepler described planetary orbits successfully as :10 0 of Perfect circles around the Earth, carrying epicycles on which the planets were actually moving. 2.Perfect circles around the sun, with no need for epicycles. 3.Perfect circles around the Earth, with no need for epicycles. 4.Ellipses with the sun in one focus, carrying epicycles on whith the planets were actually moving. 5.Ellipses with the sun in one focus, with no need for epicycles.

Ptolemy: Geocentric model, including epicycles 1. Imperfect, changeable Earth, 2. Perfect Heavens (described by spheres) Central guiding principles:

Johannes Kepler (1571 – 1630) Used the precise observational tables of Tycho Brahe (1546 – 1601) to study planetary motion mathematically. 1.Circular motion and Planets move around the sun on elliptical paths, with non-uniform velocities. Found a consistent description by abandoning both 2.Uniform motion.

Kepler’s Laws of Planetary Motion 1.The orbits of the planets are ellipses with the sun at one focus. c Eccentricity e = c/a e = 0  perfect circle e = 1  straight line

2. A line from a planet to the sun sweeps over equal areas in equal intervals of time. Fast Slow

3.A planet’s orbital period (P) squared is proportional to its average distance from the sun (a) cubed: P y 2 = a AU 3 (P y = period in years; a AU = distance in AU) Kepler’s Third Law Orbital period P known → Calculate average distance to the sun, a: a AU = P y 2/3 Average distance to the sun, a, known → Calculate orbital period P. P y = a AU 3/2

On their orbits around the sun, the planets are :10 0 of Not accelerated: Their velocity remains constant. 2.Always accelerated in their current direction of motion. 3.Always accelerated perpendicular to their current direction of motion, towards the center. 4.Always accelerated in the direction opposite to their current direction of motion. 5.Always accelerated perpendicular to their current direction of motion, away from the center.

Velocity and Acceleration Acceleration (a) is the change of a body’s velocity (v) with time (t): 1.Acceleration in the conventional sense (i.e. increasing speed) a =  v/  t Different cases of acceleration: Velocity and acceleration are directed quantities (vectors)! 3.Change of the direction of motion (e.g., in circular motion) 2.Deceleration (i.e. decreasing speed) a v

A wavelength of 650 nm is in the … range of the electromagnetic spectrum. :10 0 of Infrared 2.Optical 3.Radio 4.Ultraviolet 5.X-ray

Wavelengths and Colors Different colors of visible light correspond to different wavelengths Å = 400 nm 7000 Å = 700 nm

The Electromagnetic Spectrum Need satellites to observe Wavelength Frequency High flying air planes or satellites

The resolving power of a telescope depends primarily on its :10 0 of Diameter. 2.Primary focal length. 3.Ratio of focal lengths of the primary and secondary optics. 4.Focal length of the secondary mirror. 5.Ratio of diameter to focal length.

The Powers of a Telescope (II) 2. Resolving power: Wave nature of light => The telescope aperture produces fringe rings that set a limit to the resolution of the telescope.  min = 1.22 ( /D) Resolving power = minimum angular distance  min between two objects that can be separated. For optical wavelengths, this gives  min = 11.6 arcsec / D[cm]  min

The central temperature of the sun is approcimately :10 0 of ,800 K 2.10,000 K 3.1 million K 4.15 million K 5.1 billion K

Energy generation in the Sun: Fusion of Hydrogen into Helium Basic reaction: 4 1 H → 4 He + energy 4 protons have 0.048* kg (= 0.7 %) more mass than 4 He.  Energy gain =  m*c 2 = 0.43* J per reaction. Need large proton speed (  high temperature) to overcome Coulomb barrier (electromagnetic repulsion between protons). Sun needs reactions, transforming 5 million tons of mass into energy every second, to resist its own gravity. T ≥ K = 10 million 0 K Central temperature of the sun: ~ 15 million o K.

How do sun spot regions appear when viewed in X- rays? :10 0 of Darker than the average surface of the sun. 2.Just as bright as any other part of the surface of the sun. 3.Much brighter than other parts of the surface of the sun. 4.No X-rays can be observed from anywhere on the sun’s surface. 5.Depends on whether the sun is near solar maximum or minimum.

Solar Activity, seen in soft X-rays