Astronomy Flashcards
Celestial Object
Any object beyond the atmosphere of the earth (examples: Sun, Moon, stars, meteor)
Apparent Daily Motion
The appearance that the sun, moon, and other celestial objects move across the horizon daily in an arc (rising and setting)
Rotation
Turning of a body on an axis (like a spinning top)
Axis
Imaginary line from the North to the South pole, about which the Earth rotates
Revolution
The motion of one body traveling around another body (as the Earth travels around the Sun)
The Earth ___ around the sun once every ___ and ___ on its axis once every ___. Because of ___ there is day and night. Because of ___ there are seasons.
revolves 365.25 days (year) rotates 24 hours (day) rotation revolution
The Earth rotates from ___ to ___, ___ degrees per day or ____ degrees per hour.
West
East
360
15
The speed of rotation of a point on the surface depends on ___. This speed is greater at the ____ and least at the ____.
Latitude
Equator
Poles
Apparent Diameter
The diameter than an object appears to be to an observer. Closer objects appear larger than more distant ones even though they may not be.
The apparent diameter of the Moon is is ___ that of Jupiter; even though Jupiter is much ____ than the moon
larger
larger
Name the eight phases of the moon
New New Crescent (Waxing?) First Quarter New Gibbous Full Old Gibbous (Waning?) Third Quarter Old Crescent
Why does the moon appear to us in different phases?
Although the Moon is a sphere and should appear as a circle in the sky, we sometimes see it as a crescent or half moon because of the Sun’s relative position to the moon. The shape we see is the portion lit by the sun.
What is the period from one full moon to the next?
29.5 days
The Earth’s path around the sun is called an ___. The shape of this path is an ___, of which the sun is one of the ____. This resembles a flattened ___. This degrees of flatness is called an ___.
Orbit Ellipse Foci Circle Eccentricity
An ellipse has two ___ (singular and ____). The ___ is the longest possible distance across the ellipse. As the two ___ are brought closer together, the shape approaches a ____
Foci Focus Major axis Foci Circle
Define perihelion. On which day of the year does it occur? What is its distance to the Sun?
The point in the Earth’s orbit where it is closest to the Sun. Occurs near January 3, when the Earth’s distance from the Sun is approximately 147 million km. Thus, the Southern Hemisphere’s summer is slightly warmer and its winter slightly colder.
Define aphelion. On which date of the year does it occur? What is its distance to the Sun?
The point in the Earth’s orbit when it is farthest from the Sun. It occurs around July 4, when the Earth’s distance from the Sun is approx. 152 km.
Gravitational force between the Sun and the Earth is strongest at ___. The Sun’s orbital kinetic energy is greatest at ___. The Earth’s velocity is slowest at ___. The Earth’s potential energy decreases between ___ and ___.
Perihelion Perihelion Aphelion Aphelion Perihelion
Period of a Planet and example of planet with year longer than ours.
The amount of time it takes a planet to complete one revolution around the Sun. The length of a planet’s year. The length of a year on the planet Neptune is much longer than ours.
Astronomical Unit
The average distance from the Earth to the Sun (approx. 150 million km)
State the formula for Kepler’s Law of Planetary Motion
T^2=R^3
T=period of a planet (in Earth years)
R=radius of a planet (in astronomical units)
Solar system
A group of planetary bodies orbiting a star
The center of our solar system is ___/ There are ___ planets. It is in the ___ galaxy and is about ___ years old.
The Sun
Eight
Milky Way
4.6 billion
List the eight (formerly nine) planets in our solar system from closest to the farthest from the Sun.
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto (demoted to "dwarf planet" in 2006)
What is the Earth’s approx. mass, diameter, and average density?
6x10^24 kg
- 3x10^4 km
- 5 grams/mL (or 5.5 cm^3)
What is the Moon’s approximate mass, diameter, and average density?
7.4 x 10^22 kg
3500 km (2150 miles)
3.3 grams/milliliter
What is the Sun’s approximate mass, diameter, and average density?
2x10^30 kg
- 4x10^6 km
- 4 grams/milliliter
The Sun’s mass is about ___ times that of Earth
300,000
The Earth’s density is about ___ times that of the Sun.
2.4
The Moon’s radius is about ___ that of Earth.
1/100
Mercury’s vital statistics:
- diameter
- mass
- density
- gravity
- number of moons
- length of a day
- length of a year
- distance from the sun
- 4800 km
- 1/20 of Earth’s
- 5.7g/mL
- 1/3 of Earth’s
- none
- 60 Earth days
- 1/4 Earth years
- 58 million kilometers
Venus’ vital statistics:
- diameter
- mass
- density
- gravity
- number of moons
- length of a day
- length of a year
- distance from the sun
- 12,000km
- 4/5 of Earth’s
- 5.2 g/mL
- 9/10 of Earth’s
- none
- 243 Earth days
- 3/5 Earth years
- 107 million km
Mars’s vital statistics:
- diameter
- mass
- density
- gravity
- number of moons
- length of a day
- length of a year
- distance from the sun
- 6700 km
- 1/10 of Earth’s
- 3.9 g/mL
- 2/5 of Earth’s
- 2
- 1 Earth day
- almost 2 Earth years
- 226 million kilometers
Jupiter’s vital statistics:
- diameter
- mass
- density
- gravity
- number of moons
- length of a day
- length of a year
- distance from the sun
- 142,000 km
- 320 times Earth’s
- 1.3 g/mL
- 1/2 of Earth’s
- 15
- 10 Earth hours
- 12 Earth years
- 775 million km
Saturn’s vital statistics:
- diameter
- mass
- density
- gravity
- number of moons
- length of a day
- length of a year
- distance from the sun
- 121,000 km
- 95x Earth’s
- 0.6 g/mL
- 1.2 times Earth’s
- 18
- 10 Earth hours
- 29 Earth years
- 1.4 billion kilometers
Uranus’s vital statistics:
- diameter
- mass
- density
- gravity
- number of moons
- length of a day
- length of a year
- distance from the sun
- 47,000 km
- 15 times Earth’s
- 1.6 g/mL
- almost the same as Earth’s
- 5
- 23 Earth hours
- 84 Earth years
- 2.9 billion km
Neptune’s vital statistics:
- diameter
- mass
- density
- gravity
- number of moons
- length of a day
- length of a year
- distance from the sun
- 45,000 km
- 17x Earth’s
- 2.2 g/mL
- 1.5 x Earth’s
- 8
- 22 Earth hours
- 165 Earth years
- 4.5 billion km
Pluto’s vital statistics:
- diameter
- mass
- density
- gravity
- number of moons
- length of a day
- length of a year
- distance from the sun
- 2,274 kilometers (1,413 miles)
- 4/5 of Earth’s
- 4.2 g/mL
- unknown
- 1
- 6.4 Earth days
- 248 Earth years
- 6 billion kilometers
Asteroid belt
A broad area between Mars and Jupiter containing small bodies (not exceeding 1,000km in diameter) orbiting the Sun. Largest is Ceres, approx. 1/3 the diameter of Moon. Most meteoroids come from here.
Comet
Small object (up to 10 km in diameter) made of ice and rock fragments. When orbitting close to Sun, some of the ice evaporates and “tails” of ionized gases are formed. The tail of the comet is blown away from the Sun by the solar wind, so it always points away from the Sun, even when it is moving away from it.
What is the composition of the Sun, and why is it hot?
90% hydrogen, 10% helium (with small amounts of other, heavier elements). Its tremendous energy output results from the nuclear fusion of hydrogen to helium atoms.
Crater
A depression on the surface of a planet formed when a meteorite collides with it.
Why does the Moon have many more craters than the Earth?
The Moon has very little atmosphere to slow down meteors. Also, erosion, mountain formation, and other geologic events have obscured most of the craters on the Earth.
Define galaxy and state three basic types.
A cluster of billions of stars
- Spiral
- Irregular
- Elliptical
How long does the rotation of the earth on its imaginary straight line take?
23 hours, 56 mins, 5 seconds
What is a sidereal day?
the amount of time required for a reference star to cross the meridian
The sun is close to what degrees at its core
15 million
What is hydrostatic equilibrium?
the balance between the sun’s gravitational force and the pressure produced by its hot gases
Where in the Sun does nucleosynthesis produce heat energy and photons?
the core
Name the parts of the Sun’s atmosphere
Photosphere (surface visible for Earth)
Chromosphere (a layer outside of and hotter than photosphere)
Transition zone (region between where temps rise between chromosphere and corona)
Corona (best viewed at x-ray wavelenghts)
Solar flare
An explosive emission of ionized particles from the sun’s surface
What is the tilt of Earth’s axis?
23.5 degrees
What is the ecliptic?
The sun’s apparent path through the sky which crosses Earth’s equatorial plane twice during year
Describe the fission model of Moon Origin
Model that suggests that Moon is actually a piece of the earth that split off early during planet formation
Describe the capture model of the moon
The moon formed elsewhere in the solar system and was captured by Earth’s gravitational field
Describe the double impact model of the Moon
Earth and the Moon formed during same period of time from samd accretion material
What is the fourth and most widely acception hypothesis about the Moon?
The collision between earth and large asteroid which released a large amount of Earth’s crustal material into its orbit; Moon accreted from that material and the material diplaced from the asteroid due to the collision
Why is the same side of the moon always facing earth?
the mutual gravitational pull between the two bodies
sidereal period of the moon
27 days
What is the time of the lunar month (or time it takes for Moon to return to a certain alignment viewed from earth)
29 days, 12 hours, 44 mins, 28 secs
What are terrestrial planets?
This refers to the four planets closer to sun - Mercury, Venus, Earth, Mars) and are classified because of these similarities:
High densities and atmospheres that consistute small % of masses
Atmospheres mostly heavy elements
Magnetic fields
Various levels of internally generated activity that caused the planets to evolve
Volcanic activity on all of these except Venus
Two Martian satellites that have been observed
Phobos
Deimos
Each is ellipsoidal
Giant planets
Large diameters - Jupiter, Saturn, Uranus, and Neptune
Hypothetical icy cores
Atmospheres mostly hydrogen and helium
Not a solid surface
Uranus is only giant planet that exhibits no evidence of internal activity
Rings
The 4 giant planets exhibit these. They are flat disks of fragmented material that orbit. Many of the smaller satellites are embedded.
Describe the two main hypotheses about rings
- Tidal force exerted on a satellite by its planet may surpass the Roche limit (point at which particle cohesion is no longer possible) and break the satellite into fragments which then collide and become smaller. That material spreads out into ring.
- Unaccreted material leftover after formation of the planets, Below the Roche limit (within a certain vicinity to the planet), these particles could not join together to form satellites and would settle into orbital rings
Satellites
Jupiter has over 50 known satellites
Io (Jupiter’s moon) is the only celestial body besides Earth known to be currently volcanically active
Saturn has 21 satellites. (Titan has its own atmosphere)
Uranus has 5 (with topography)
Neptune has 8 - Triton also has atmosphere
Double-planet system
Charon and Pluto
Similarity in size
Large levels of methane absorbed into ice
Charon resembles the Uranian satellites more than Pluto
Describe 3 Kepler’s Laws (1600s)
- each planet moves in its own elliptical path and all these orbits have Sun as singular focal point
- straight line between planet and the Sun sweeps out equal areas in equal time (move quickerr in part of orbit closest to sun)
- further a planet is from the Sun, the longer its orbital period will be
3 stellar properties
position, brightness, spectra
Positional stellar observation
Principally performed through study of the positions of stars on multiple photographic planes
Parallax
a star’s apparent shift in position due to revolution of Earth around the sun; can be used to establish distance to a star
Brightness
Categorization of stars according to magnitudes. Fixed intensity ratio between the six magnitudes.This gives indication of temperatuer
Spectra
provides info about temperature of stars - higher star’s temp, more ionized the gas in outer layer. A star’s spectrum also relates to the chemical composition.
Binary star system
two starts that orbit each other (common)
Visual binary
A pair of stars that can be visually observed
Hertzsprung-Russell (H-R) Diagram
helps explore relationships between the luminosities and spectral qualities of stars. Involves plotting those qualities on a graph with absolute magnitude (luminosity) on the vertical and spectral class on horizontal.
Helps tell where they are in stellar evolution.
Low temp, high luminosity = giants, supergiants
High temp, low luminosity = white dwarfs
Stellar evolution: low mass stars become ____ while high mass stars become ____
white dwarfs
supernovae
How is a star born?
Protostar is formed from collapsing interstellar cloud. Temp at center of protostar rises, allowing nucleosynthesis (hydrogen burning through fission) to begin. Eventually star runs out of fuel (H)
What happens when a low mass star runs out of Hydrogen?
The star will contract due to gravity which will raise the temp just outside the core to a point at which nucleosynthesis and different fusion (with helium) can produce a carbon nucleus. This becomes a red giant (OUR SUN)
What happens when a red giant’s stage is over?
Gravity becomes active again and shrinks star until the degeneracy pressure of electrons begins to operate, creating a white dwarf that will eventually burn out. If it’s a high mass star it will move on to a supernova.
Supernova
Once helium burning is complete, mass causes core temp to rise, enabling fusion of carbon then silicon and other atomic nuclei (each in a new shell further out of core). When fusion cycle reaches iron, a core begins to form, which accumulates over time. Eventually, the temp and pressure are high enough for electrons to interact with protons in the iron nuclei and produce neutrons. The core falls and collides with the star’s outer envelope causing a massive explosion (supernova). This continues until neutrons exert degeneracy pressure; this creates a pulsar. In more massive stars, nothing can stop it which ends in a black hole
Meteoroid
small, solid fragment of material in solar system. METEOR is used to refer to this body when it enters Earth’s atmosphere.
What causes meteors to break up?
Interaction / friction between meteors and upper levels of atmosphere
What creates the phenomena of shooting stars?
The heat associated with frictional forces causes meteors to glow
What are meteorites?
These are meteors that are large enough to avoid complete disintegration and can therefore travel all the way down through atmosphere to earth’s surface
Asteroid
Small, solid planet (planetoid) that orbits sun. Orbital paths of most are between Jupiter and Mars (asteroid belt). They tend to be carbonaceous and are divided into groups based on distance from a large, named asteroid
Sub-groups of asteroids
Atens - lie between earth and sun
Apollos - mimic Earth’s orbit
C-type - compositions similar to sun and dark
S-type - nickel-iron and iron and magnesium silicates
M-type - bright asteroids made exclusively of nickel-iron
The space between planets and stars
Interstellar medium
Tiny solid bodies called interplanetary dust (grains mostly tiny fragments of nuclei of dead comets)
dead stars and gases exist there too
Black holes populate interstellar medium and are a form of dark matter; trap photons
Dark matter
bodies we cannot see. (could be MACHOS or WIMPS) but def. mysterious
The moon’s orbit is off __ degrees from the ecliptic
5
Characteristics of Milky Way
- Spiral galaxy
- consists of central, bulging disk called nucleus
- most of its light comes from stars in this region
- disk surrounded by halo of stars and star clusters that spread above, next to, and beneath nucleus
- globular clusters (clusters of ancient stars) found in halo
- spiral arms of high luminosity stars fan out from nucleus
- entire thing rotates around center
Elliptical galaxies
Roughly spherical
Subgroups based on degree of flattening in shape from E0 (spherical) to E7 (flat)
Model of the Inflationary Universe
Hubble’s law states that speed at which galaxy appears to be moving away from Earth is proportional to its distance from earth.
v=Hr
v= velocity of receding galaxy
r = distance from earth
H=hubble constant
Hubble’s model contends that the universe is expanding, that it began at a specific point in the past. A random grouping of quarks and leptons along with a strong force existed in the early universe and then seperated out ffrom the mass. This rapid expansion formed universe.
