Ch. 8: Astronomy 01

Members of the solar system

planets, dwarf planets, moons, asteroids, comets, Kuiper Belt objects, interplanetary dust & gas

dwarf planets vs. planets

planets: contain enough mass to be sufficiently round AND have a clear orbit

dwarf planets: contain enough mass to be sufficiently round, but LACK a clear orbit.

planet vs. star

Stars are larger, hotter, and generate light via nuclear fusion.

Planets are less massive, colder, and shine light by reflecting stars.

Solar Nebula Model & evidence

Model: The solar system formed out of an eastward rotating interstellar cloud around the sun 4.6 billion years ago. The nebula contracted into disks surrounding the proto-Sun. Planets formed out of dust and gas from that nebula.

Evidence: All of the planets & celestial objects in our solar system orbit the sun clockwise, just like the interstellar cloud! (This movement is called a direct motion).

Ecliptic

The mean plane of earth's orbit (and the other planets')

Inferior planets

planets whose orbits are closer to the sun than earth:

Mercury & Venus

Superior planets

planets whose orbits are farther from the sun than earth:

Mars, Jupiter, Saturn, Uranus, Nepturn

Earth's only natural satellite

the moon!

Waxing

Moon grows bigger

Waning

Moon grows smaller

New moon

rises at sunrise, sets at sunset

dark because dark side faces earth

moon waxes after

First quarter

7 days after new moon

Has traveled 1/4 way around earth

Rises noon, sets midnight

Waxing gibbous

Over 1/2 moons brightness visible from earth

Full moon

2 weeks after new moon

12.37 times per year

Rises sunset, sets sunrise

Waning gibbous

Over 1/2 moons brightness visible from earth

Third quarter

Has traveled 3/4 way around earth

Rises midnight, sets noon

Waning crescent

phase of the moon that comes after a last quarter moon and before a new moon where only the left sliver of the moon is visible and has a crescent shape

Blue moon

Every 2.72 years per each month

Every 19 years for each month

sydonic month/ lunation

29.5 day moon cycle

Maximum elongation for Venus

48 degrees

Maximum elongation for Mercury

28 degrees

retrograde motion of planets

The apparent motion of the planets when they appear to move backwards (westward) with respect to the stars from the direction that they move ordinarily.

retrograde loop

the planets bounce back to the direct motion after taking a little retrograde motion

geocentric model / Ptolemaic system

solar system moves in epicycles around Earth, on deferents!

150 A.D. Greek Astronomer: Ptomely

heliocentric model / Copernican system

The wandering motion of planets results from the orbital motions of planets around the sun!

Galileo

- first person to use telecsope for scientific observations (1609)

- Observed Venus appears to change size regularly due to its inferior and superior conjuction

Inferior conjuction

An inferior planet appears as a crescent and biggest during inferior conjunction: the points between sun and earth

superior conjunction

An inferior planet looks most fully lit in its gibbous phase, near superior conjunction: the point on the far side of the sun from earth

Tycho Brache (1546 - 1601 AD)

Danish astronomer who predicted star and planet positions with very good accuracy

Inspired Kepler's Laws

Kepler's Laws

1. Each planet moves around the sun with an orbit that is an ellipse

2. Planets move faster when they are closest to the sun (perihelion) and slowest when they are farther away (aphelion)

3. d3 = p2

p = the periods of time required for any two planets to complete a trip around the Sun.

d = their average distances from the Sun.

Kepler's third law can be used to find a planet's average distance, d, from the Sun compared to Earth's average distance of 1 AU (Section 4.2). The planet's orbital period, p, in years is found from observations.

An ellipse

the distance from the center to a vertex

Newton's Laws

1. no force means no acceleration, concept of inertia

2. F_net = ma, concerned with 1 object

3. objects exert the same force on each other in opposite directions, concerned with 2 objects

units: N = kg*m/s^2

Newton's Law of Gravity

Every object attracts every other object with a force that is proportional to the product of the two masses and inversely proportional to the square of the distance between them.

sideral month

27.3 Days: The amount of time it takes the Moon to revolve around the Earth and line up with the same star again

Perigee

point in an orbit that is closest to the Earth

apogee

the point in an orbit most distant from the body being orbited; the highest point

Syzgy

three things in a line, original moon sun and earth

satellite

any body in an orbit with a larger planet body

minimum forward velocity for artificial satellites

8 km/sec

what keeps satellites in their orbits?

their forward motion + their motion towards earth, caused by earth's gravity

How robot spacecraft send data back to earth

radio waves

Gravity assist

a technique using a planet's gravitational field to change a spacecraft's velocity without consuming fuel

ex. use to increase Voyager's speed and bend its flight path

comparative planetology

The study of the solar system by examining and understanding the similarities and differences among worlds

terrestial planets

near the sun

small diameter

small mass

high density

giant planets

far from the sun

large diameter

large mass

low density

period of revolution

length of time for a celestial body to go around its orbit once

Sidereal Revolution Year

length of planet's orbit in terms of earth time

Synodic Revolution Period

planet's orbit period as seen from earth

equal to the time it takes to turn to the planet's specific aspect (position relative to sun), such as conjunction

Period of rotation

length of time for a celestial body to turn around its axis once

sidereal rotation period

length of one sidereal day on a planet

synodic rotation period

length of one synodic day on a planet

C-type asteroids

Carbonaceous asteroids...they are the most common variety, forming around 75% of known asteroids.

In outer belt

very dark

S-type asteroids

moderately bright

contain silicates + metals

in inner belt

M-type asteroids

very bright

metallic

probally condensed from OG solar nebula, but never got big enough to form a planet

Near Earth Objects (NEOs)

asteroids and comets that regularly come near by

ex) apollo and amor asteroids

apollo asteroids

some 50 asteroids with diameters larger than 1 km that have eccentric orbits that cross the Earth's orbit to their perihelion

amor asteroids

orbits between 1-1.3 AU, stays beyond earth's orbit

Kuiper Belt Objects (KBOs)

small icy objects, beyond neptune, that orbit the sun in the Kuiper belt

exist from planet formation (leftovers that never collided into planets)

Kuiper Belt

A region of the solar system that is just beyond the orbit of Neptune and that contains small bodies made mostly of ice

30-55 AU, near ecliptic plane

named after Gerard Kuiper

How robot spacecraft send data back to earth