Astronomy 101 Test 1

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Terms in this set (...)

Star
A sphere of gas shining under its own power
Latitude vs. Longitude
Latitude is horizontal and longitude is vertical
Celestial sphere
The imaginary sphere on which objects in the sky appear to reside when observed from Earth
Standing at 30 degree north latitude (San Diego)
Polaris is always located 30 degrees above northern horizon. Stars within 30 degrees of north star are circumpolar; other stars rise and set at an angle to the horizon
Ecliptic
Apparent annual path of the sun on the celestial sphere.
Asterism
An especially notable star pattern in the sky. Example asterism: Big Dipper
Zodiac
A belt around the sky around 18 degrees wide, centered on the ecliptic
Parallex
The apparent displacement of an object caused by a change in the position from which it is viewed. The closer the object, the greater the parallax
Cosmology
The study of the Universe as a whole: its contents, structure, origin, evolution, and ultimate fate
Aristotle
A very influential Greek philosopher who presented arguments in favor of Earth having a spherical shape (325 BC)
Eratosthenes
Greek astronomer and geographer; he calculated the circumference of the globe using careful observations and simple geometry (200 BC)
Hipparchus
Perhaps the greatest observational astronomer of ancient times (150 BC), responsible for creating a precise star catalog (locations and brightnesses) and discovering the precession of Earth's axis
Tetrabiblos
The foundational book on astronomy, written by Ptolemy (who also wrote the Almagest) in 140 AD
Epicycle
A small circle riding on a larger circle on which the planet moves
Nicholas Copernicus
He thought that the Sun was the center - first to think since Aristarchus
Geocentric vs. Heliocentric
Geocentric was favored by ancients, perfected by Ptolemy (130 AD)
Heliocentric cosmology not proposed until Copernicus (1540 AD)
Venus observations
Only the heliocentric model is consistent with the observation that Venus goes through a complete set of phases
Correct explanations (heliocentric cosmology) for observations
1. Occurs due to the Earth rotating once per DAY about its axis of rotation.
2. Occurs due to the Earth revolving once per YEAR around the Sun.
3. Occurs due to Earth passing outer planets in their paths around the Sun.
4. Occurs due to Mercury and Venus always being interior to the Earth's path around the Sun.
Seasons
Caused by the tilt of Earth on its axis as it revolves around the Sun
Precession
The slow, conical change in the orientation of Earth's axis of rotation that slowly changes the location of the celestial poles over time (26,000 years)
Galileo's Telescope Observations
a) Phases of Venus
b) Jupiter's moons
c) Moon's craters
d) Sunspots
e) Milky Way made of innumerable stars
Galileo's Contributions
-Emphasized experimentation
-Law of Falling Bodies: in the absence of air-resistance, all bodies fall at the same rate
-Law of Inertia: Every body tends to continue doing what it is already doing -- being in a state of rest, or moving uniformly in a straight line -- unless it is compelled to change by an outside force
-Principle of Equivalence: There is no way to tell locally the difference between being in a reference frame that is at rest or one that is moving at a constant speed in a constant direction
Foucault Pendulum
A freely swinging pendulum whose apparent change in direction demonstrates that the Earth is rotating
Kepler's question
What are the precise paths taken by the planets as they revolve around the Sun?
Newton's question
Why do they planets follow the paths that they do?
Asteroid
A small, stony or metallic object orbiting the Sun
Asteroid belt
A region between the orbits of Mars and Jupiter in which many asteroids are located
Comet
A small body of icy and dusty matter that orbits the Sun. Highly eccentric!
Volume vs. Density
Volume - the physical space occupied by a body
Density - amount of mass per unit volume
Angular momentum
The momentum associated with motion around an axis or fixed point
Newton's Law of Gravitation
F=Gm1m2/r^2
If you double the distance, the force decreases by a factor of 4
If you halve the distance, the force increases by a factor of 4
Kepler's Three Laws of Planetary Motion
1. Each planet moves about the Sun in an orbit that is an ellipse, with the Sun at one focus of the ellipse
2. The straight line joining a planet and the Sun sweeps out equal areas in space in equal intervals of time
3. The squares of the planets' periods of revolution are in direct proportion to the cubes of the semimajor axes of their orbits. P^2 = a^3
Newton's Version of Kepler's Third Law
The mass is equal to the sum of the Sun and planet's masses. The shorter the period (i.e. the faster the orbit), the greater the mass causing the orbit
Solar system
The system of the sun, planets, and other objects revolving around the Sun
Why are eclipses rare?
Because the moon orbits Earth on a 5 degree incline
Solar eclipse
The eclipse of the Sun by the Moon, caused by the passage of the moon in front of the Sun
Angular size
The angle subtended by an object in the sky, typically measured in degrees. The Sun looks to be the same size as the Moon
Planetseimals
Small bodies that formed in the solar nebula that ultimately formed the planets
Terrestrial Planets
Inner planets - Mercury, Venus, Earth, Mars
Jovian (Giant) Planets
Outer planets - Jupiter, Saturn, Uranus, Neptune
Differentiation
The gravitational separation of materials of different density into layers in the interior of an object - centers of planets are more dense
Meteor
A flash of light caused when a particle from space burns up in our atmosphere (i.e. shooting star)
Meteroid
A particle or chunk of typically rocky or metallic material in space before any encounter with the Earth
Meteorite
A portion of a meteoroid that survives passage through Earth's atmosphere and strikes the ground (ex: crater in AZ)
Mercury
Geologically dead (no volcanoes, water, etc.)
No atmosphere to protect against particles
No moons
Venus
Thick atmosphere
Experiences "runaway" Greenhouse effect
No moons
Backward rotation
The Moon
Orbits Earth every 27 days
Very BIG relative to Earth
Has no atmosphere
Mars
Comparatively small planet
Rotates every 24 hours (like Earth)
Has largest volcano in Solar System
Has two small moons (probably captured asteroids)
Jupiter
Largest and most massive
No solid surface
Similar chemical composition to the Sun
Over 60 known moons
Jupiter's Moon, Ion
Most active surface in our Solar System (a ton of volcanoes)
Saturn
No solid surface
Least dense of all of the planets
Over 60 known moons
Uranus
First planet discovered by telescope (1781)
No solid surface
Over 25 known moons
Neptune
Predicted by mathematical calculation then discovered (1846)
Similar in size to Uranus
Over a dozen known moons
No solid surface
Pluto (dwarf planet)
Was visited by "New Horizons" spacecraft in 2015
Has 5 moons
Has a solid surface
Has an extremely inclined orbit and is more eccentric
Smaller than Earth's moon!
A planet is a body that...
Is an orbit around the Sun
Is nearly round in shape
Has "cleared the neighborhood" around its orbit