Astronomy 1000- Exam 1

Celestial Poles

Projection of Earth's axis onto the sky

Celestial Equator

Projection of the equator onto the sky

Zenith

Straight overhead

Horizon

90 degrees from the zenith

Meridian

North-South line through the zenith

Altitude/Direction

Coordinates on the sky

Astronomical Unit (AU)

1.5 X 10^8 km

Latitude

Position north or south of equator

Longitude

Position east or west of prime meridian

Circumpolar

Perpetually above the horizon

Direction of stars, sun, and moon

Rise in East, Set in West

Solstice

Sun is at maximum distance north or south of Celestial Equator

Equinox

Sun crosses Celestial Equator

Precession

Subtle change in Earth's rotation axis. Axis precesses like a spinning top, polaris won't always be the North Star

Axial Tilt

Key to the seasons; Earth's axis points in the same direction (to Polaris) all year round

One Lunation

One circuit through the phases. Lasts 29.5 days

Phases of the moon

1) New

2) Crescent

3) First Quarter

4) Gibbous

5) Full

6) Gibbous

7) Last Quarter

8) Crescent

Waxing

Getting brighter, appears in evening sky

Waning

Getting dimmer, appears in the morning sky

Lunar Eclipses

Earth blocks the Sun (Earth's Shadow on moon), only occurs at full moon. 3 types of lunar eclipses: penumbral, partial, or total

Solar Eclipses

Moon blocks Sun, can only occur at new moon. 3 types: partial, total, or annular

Nodes

Moon's orbit is slightly inclined (by about 5 degrees) to the ecliptic plane (plane of Earth's orbit around the Sun). The two points in each orbit at which the Moon crosses the surface are called the nodes

Principles of Science (Good Theories must be)

Mechanistic- phenomena follow rules

Consistent- same thing happens each time

Testable and Predictive- falsifiable

Simple-

Mediocre- Can't assume we are in a special position

Deductive- theory fits observations, not vice versa

Retrograde Motion

Planets apparently reverse direction of orbit for a couple weeks to a month in the night sky. Hard to explain when believing in geocentric model.

Parallax

Small shift in angular position when viewed from different places. The farther away something is, the smaller it's parallax.

Speed

Distance per time (m/s)

Velocity

Speed with direction

Acceleration

Change in velocity (m/s^2)

Momentum

Mass X Velocity

- forces change momentum

Angular Momentum

Mass x Velocity x Radius

Kepler's Laws

1) The orbit of each planet is an elliptical around the Sun, with the Sun at one focus

2) As a planet moves around its orbit, it sweeps out equal area in equal time

3) Distant planets orbit the sun at slower average speeds: p^2=a^3, orbital years=semi-major axis

Newton's 3 Laws of Motion

1) Inertia: An object moves at constant velocity if there is no net force acting on it

2) F=MA: A force F acting on a body of mass M produces an acceleration A

3) Action-Reaction: For any force, there is an equal and opposite reaction force

Energy of orbit

Proportional to the average distance from the Sun

Aphelion

Distance farthest from the Sun

Perihelion

Distance closest to the Sun

Types of Orbits (4 Types)

1) Elliptical: bound, closed

2) Circular: special case of ellipse

3) Parabolic: unbound, open

4) Hyperbolic: unbound, open

Eccentricity

How much a planet's orbit differs from a perfect circle

Tides

The difference in gravitational acceleration between sides of something

Tidal forces

Try to pull orbiting bodies apart. Larger size and closer the orbit= greater tidal forces

Tidal Locking

Synchronous rotation, smaller bodies lock first since they have less angular momentum

3 Types of Planets

1) Terrestrial Planets- medium sized and rocky

2) Jovian Planets- large and gaseous

3) Dwarf Planets- small and icy

Terrestrial Planets

Medium sized and rocky

High density, solid surface

Few moons, no rings

Jovian Planets

Large size and mass

Large and gaseous

Mostly H, He, and H-compounds

Low density, no solid surface

Rings and moons

Dwarf Planets

Small and Icy

Inclined Orbits

Share orbital space with many other objects

3 Characteristics of Planets

1) Orbit Sun

2) Large enough to be spherical

3) "Cleared their orbit"

3 Characteristics of Dwarf Planets

1) Orbit Sun

2) Large enough to be spherical

3) Have not cleared their orbit

2 Types of Small Bodies

1) Asteroids

2) Comets

Asteroids

Left-over rocky planetesimals, many find their home in the asteroid belt between Mars and Jupiter (2-4 AU)

Comets

Left-over icy planetesimals, most find their home in Kuiper Belt beyond Pluto (30-100 AU)

Patterns in the Solar System

1) Orderly motions

2) Three kinds of planets

3) Two kinds of small bodies

4) Exception to the rules

Exceptions to the rules

Rotations: Venus rotates backwards, Uranus and Pluto rotate sideways

Orbits: Triton orbits backwards

Moons: Our Moon and Charon are exceptionally big, most small moons exhibit weird orbits