Midterm 1 Review Please swipe your student ID for attendance tracking, and pick up your assigned transmitter

What is the name of the galaxy cluster containing our own galaxy? :10 0 of 5 1.The Solar System 2.The Milky Way 3.The Solar Group 4.The Local Group 5.The Local Cluster

Distance to the nearest large galaxies: several million light years The Local Group of Galaxies Galaxies usually don’t exist alone, but in clusters of galaxies

Clusters of galaxies are grouped into superclusters. Superclusters form filaments and walls around voids. The Universe on Very Large Scales

The Astronomical Unit (AU) is defined as :10 0 of The time it takes for the moon to orbit once around the Earth 2.The distance between the Earth and the moon 3.The distance between the Earth and the sun 4.The diameter of the Earth 5.The size of the solar system

9.5*10 9 equals :10 0 of ,000,000, ,500,000, ,000, ,000,000,000

Orbits in the Solar System Pluto Neptune Uranus Saturn Jupiter Mars (Distances and times reproduced to scale) Asteroids Comets ~ 50 AU

Which planet’s orbit is the most highly inclined against the ecliptic? 10 0 of Mercury 2.Venus 3.Jupiter 4.Uranus 5.Pluto

Retrograde rotationTipped over by more than 90 0 Mercury and Pluto: Unusually highly inclined orbits Planetary Orbits and Rotation

Over the course of the night, stars are rising in the … and setting in the … 10 0 of North / South 2.East / West 3.South / North 4.West / East 5.East / East

Apparent Motion of the Celestial Sphere Geographic Latitude l

Which of the following values of visual magnitudes seem correct to you? 1.A 2.B 3.C 10 0 of Object Magnitude A B C Sun Full Moon Venus Sirius

The magnitude scale system can be extended towards negative numbers (very bright) and numbers > 6 (faint objects): Sirius (brightest star in the sky): m v = Full moon: m v = Sun: m v = -26.5

Which of the following is the longest time? 10 0 of The Earth’s orbital period 2.The moon’s sidereal orbital period 3.One precession cycle 4.The moon’s synodic orbital period 5.The Saros cycle

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 w.r.t. the Ecliptic takes about 26,000 years and is called precession.

The Phases of the Moon The moon’s synodic period (to reach the same position relative to the sun) is days (~ 1 month). Fixed direction in space Earth Moon Earth orbits around Sun => Direction toward Sun changes! days

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

Spring and Neap Tides The Sun is also producing tidal effects, about half as strong as the Moon. Near Full and New Moon, those two effects add up to cause spring tides Near first and third quarter, the two effects work at a right angle w.r.t. each other, causing neap tides. Spring tides Neap tides

A Total Lunar Eclipse (II) A total lunar eclipse can last up to 1 hour and 40 min. During a total eclipse, the moon has a faint, red glow, reflecting sun light scattered in the Earth’s atmosphere. There are ~ 1 – 2 lunar eclipses per year.

An annular solar eclipse can occur when … 10 0 of The Earth is near apogee and the moon is near perihelion. 2.The Earth is near aphelion and the moon is near perigee. 3.The Earth is near perihelion and the moon is near apogee. 4.The Earth is near perigee and the moon is near aphelion. 5.Both the Earth and the Moon are near perihelion.

Earth’s and Moon’s orbits are slightly elliptical: Sun Earth Moon (Eccentricities greatly exaggerated!) Perihelion = position closest to the sun (January) Aphelion = position furthest away from the sun (July) Perigee = position closest to Earth Apogee = position furthest away from Earth

Kepler’s 2 nd Law states that … 10 0 of The acceleration of a body is proportional to the force exerted on it, divided by the mass of the body. 2.To every force there is an equal and opposite force balancing it. 3.The planets are moving around the sun on ellipses with the sun in one focus. 4.The planets are moving on circular epicycles, which, in turn, are orbiting around the sun on perfect circles. 5.A virtual line from the sun to any planet swipes over equal areas in equal amounts of time.

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

History of Astronomy – A one-slide overview Ptolemy: Copernicus: Earth in the center (geocentric Universe) perfect circles epicycles Sun in the center (heliocentric Universe) perfect circles no epicycles Galilei: First detailed telescope observations: Moons of Jupiter; rings of Saturn; phases of Venus; sunspots; surface features on the moon -> Support of Copernican model Kepler: 1.Elliptical orbits 2.Non-uniform velocities 3.Inner planets orbit faster than outer planets Newton: 1.No force => uniform, straight motion 2.Force = mass*acceleration 3.action = reaction

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