ASTRONOMY TEST 1
September 21 declination?
0°
How many degrees does Earth turn in 1 hour?
15°
If a star is 34 light years away, how long or how much time did it take the light from the star to reach Earth?
34 years
How far can moon get from ecliptic?
5°
The Sun is almost 400 times farther from Earth than is the Moon. How long does light from the Moon take to reach Earth?
8/400 = .02 minutes = 1.2 seconds
If an observer is at 47° N latitude, what is the height of the sun at noon if the date is December 21? (know how to do the math)
90° - 47° = 43° 43° - 23.5° = 19.5° Height = 19.5°
360°/ 4 seasons
90° between each season
Star at Meridian @10:00 pm. What time will it be at the Meridian tomorrow?
9:56 pm
Kepler's 3rd Law
Exists a relationship between orbital distance from the sun and orbital period, such that the farther away a planet is from the sun, the longer it takes to orbit the sun
What are the largest known structures in the universe?
Filaments (clusters of superclusters)
If today is September 21, and the moon is at the location of the Winter Solstice along the ecliptic, what is the phase of the moon? (know drawing)
First Quarter
Phase rising at noon?
First Quarter
What is the phase of the moon that rises at local noon? (know drawing of ALL phases of the moon)
First Quarter
Phase for lunar eclipse?
Full
Solar eclipse?
Full Moon
Retrograde motion?
Westward
How does the date of the beginning of summer in Earth's Southern Hemisphere differ from the date in the Northern Hemisphere?
When summer is beginning in the Southern Hemisphere, the Northern Hemisphere begins experiencing a different season. Seasons arise because Earth's axis is not perpendicular to its orbit.
Why does the number of circumpolar constellations depend on the latitude of the observer?
When traveling between higher and lower latitudes, you can observe different circumpolar constellations. Circumpolar constellations rotate around the poles.
What season has declination -5°?
Winter
How long does it take light to cross the diameter of the Milky Way Galaxy?
Would take 80,000 years to cross diameter
If you are at latitude 30° N of Earth's equator, what is the angular distance from your zenith to the NCP? From your nadir to the NCP?
Zenith to NCP: 60° Nadir to NCP: 120°
Uranus orbits the Sun with a period of 84.0 years. What is its average distance from the Sun?
p^2 = D^3 (84)^2 = D^3 √7056 = √D^3 19.2 AU
If a planet has an average distance from the sun of 2.0 AU, what is its orbital period?
p^2 = D^3 p^2 = (2)^3 √p^2 = √8 p = 2.82 years
Astronomy
study of moon, sun, stars (content of universe)
About how many days must elapse between first quarter moon and third quarter moon in the same cycle?
About 14 days
White Dwarfs, Neutron Stars, and Black Holes are all the result of what event in the life of a star?
Star Deaths
Identify the phases of the Moon if at the sunset in the Northern Hemisphere the Moon is: (a) near the eastern horizon (b) high in the southern sky (c) in the southeastern sky (d) in the southwestern sky
(a) Full Moon (b) First Quarter (c) Waxing Gibbous (d) Waxing Crescent
Identify phases of the moon if on March 20 the moon is located at the point of the ecliptic called: (a) Vernal Equinox (b) Autumnal Equinox (c) Summer Solstice (d) Winter Solstice
(a) New Moon (b) Full Moon (c) First Quarter (d) Third Quarter
For an observer at latitude 36° N, what is the declination of stars found at the zenith? (know how to the drawings)
+36°
Declination of NCP?
+90°
Hipparchus
- Compiles first star atlas with a magnitude or brightness scale for the stars Discovers procession of the Earth
Erastosthenes
- Computes the size of Earth
Aristarchus of Samos
- Develops mathematical method for measuring distances to Sun, Moon, Planets Proposes Heliocentric model (rejected; did not show parallax)
Galileo
- First person to use a telescope to view the Universe (did not invent) - Discovers: craters, maria, mountains all on moon; sunspots on the Sun and solar rotation; rings of Saturn; Milky Way is full of stars; large 4 moons of Jupiter; phases of Venus - Prohibited about his findings with the Copernician model (findings supported his model)
Tycho
- Last great naked eye observer - Used parallax technique to prove comets are out in space, not Earth's atmosphere
Copernicus
- Proposed Heliocentric model - Fatal flaw: circular orbits (should be elliptical)
Aristotle
- Proves Earth is a sphere - Introduces Geocentric Universe Model
Ptolemy
- Publishes Geocentric model (improvement of Aristotle) - Incorporates deferents and epicycles - System Order 1. Earth 2. Moon 3. Mercury 4. Venus 5. Sun 6. Mars 7. Jupiter 8. Saturn 9. Fixed Stars
Kepler
- Tycho's assistant - Developed 3 laws of planetary motion from Tycho's data he inherited - Laws support the Copernician view and go far beyond
For an observer at 54° N latitude, what is the declination on the south horizon?
-36°
For an observer at latitude 39° N, what is the angular width of sky circumpolar for this location? What is the range of declinations circumpolar from this latitude?
1. 78° 2. +90° to +51°
Explain two reasons winter days are colder than summer days.
1. Duration of daylight: the amount of time the surface is exposed to radiation from the Sun 2. Sun is lower in the sky where it happens to be winter time, delivering less energy per unit area on the surface of the Earth
What three conditions are necessary for a total solar eclipse?
1. New moon 2. Perigee 3. Node point
Real Answers to Planetary Motion
1. Retrograde motion occurs when planets pass each other 2. Venus and Mercury are inner planets, thus close to the Sun in our sky 3. Changing distances create brightness and speed changes
Universe (order of scale; small to large)
1. Star 2. Solar System 3. Galaxy 4. Groups of Galaxies 5. Superclusters of Galaxies 6. Filaments and voids 7. Universe
Planetary Motion (any model of solar system must explain the following observations of the planets)
1. Sun and Moon seem to only move east with respect to fixed stars; planets can move east or west among the stars 2. Venus and Mercury are always observed close to the Sun in our sky; Venus never more than 46° away from Sun; Mercury never more than 28° away from Sun 3. Over several months, planets will vary in brightness and speed as seen from Earth
Kepler's 3 Laws of Planetary Motion?
1. ellipse 2. equal area equal time 3. p^2 = D^3 (further from Sun, longer it takes to orbit)
Meridian
A line drawn from due north through the Zenith down to due south across the sky
How much of the sky is circumpolar from the south pole?
All of it
If you lived on Mars, which planets would exhibit retrograde motion like that observed for Mars from Earth? Which would never be visible as crescent phases?
All planets in sky take part in retrograde motion. Outer planets, J, S, U, and N, would never be visible as crescent phases.
Fundamental Rule
An observer's latitude determines the altitude of the NCP above the north horizon and vice versa
Altitude
Angular height of a star or object above the horizon (0° to 90°)
Where are most of the asteroids found in the solar system?
Asteroid Belt
Where is the asteroid belt located?
Between Mars and Jupiter
What is a nebula?
Big cloud of dust and gas; center of star; birthplace of a star
0° Declination?
Celestial Equator
Ptolemy's model... purpose of equant point?
Change in brightness for distance
Which lunar phases would be visible in the sky at dawn? At midnight?
Dawn: full, waning gibbous, third quarter, and waning crescent Midnight: first quarter, waxing gibbous, full, waning gibbous, and third quarter
Winter Solstice
December 21; shortest day of the year
Deferent vs Epicycle
Deferent: "big circle" Epicycle: "small circle"
Comets out in space?
Discovered by Tycho
Distance Formula
Distance = (speed) x (time)
The distance unit 1 astronomical unit (1 A.U.) is based on the distance between which two bodies?
Distance between the Earth and the Sun
Geocentric
Earth centered
Light from the Sun takes 8 minutes to reach Earth. How long does it take to reach Mars, 1.5 AU from the Sun?
Earth to Sun = 1 AU to 8 minutes Mars to Sun = 1.5 AU to 12 minutes (ratio multiplication)
Prograde motion?
Eastward
Sun's path.
Ecliptic
Copernicus model?
Heliocentric
How would you define the celestial poles and equator if Earth did not rotate but kept one hemisphere constantly facing the Sun during its yearly orbit?
If Earth did not rotate, there could be no definitions of the celestial poles and equator. If Earth did not rotate, it would have no rotation axis.
Summer Solstice
June 21; longest day of the year
Latitude & Longitude
Latitude: horizontal line measuring North and South of Equator Longitude: vertical line measuring East and West of Prime Meridian
Why are light-years more convenient than miles, kilometers, or astronomical units for measuring the distances to stars and galaxies?
Light years are more convenient because light years display how far a beam of light has traveled in one year.
In Ptolemy's model, how do the epicycles of Mercury and Venus differ from those of Mars, Jupiter, and Saturn?
M and V (planets inside Earth's orbit) appear to move with smaller epicycles than those of Ma, J, and S (planets outside Earth's orbit). M and V appear between Earth and the Sun.
Vernal Equinox
March 21; equal day and night
If it is the first day of spring in your hemisphere, what day is it in the opposite hemisphere?
March 21; still this date but its the beginning of fall, not spring
On Venus, what planet has crescent?
Mercury
What is the difference between the Milky Way and the Milky Way Galaxy?
Milky Way: band of stars we can see in the night sky Milky Way Galaxy: our home galaxy
Lunar Eclipses
Moon enters Earth's shadow due to its orbital motion (a) Full Moon (b) Crossing ecliptic (c) Visible from entire night side of Earth
If you are at latitude 40° N of Earth's equator, what is the angular distance from the Northern Horizon up to the NCP? From the Southern Horizon down to the SCP?
NCP to Northern Horizon: 40° Southern Horizon to SCP: 40°
What is the angular distance from the NCP to the point on the sky called the Vernal Equinox? To the Summer Solstice?
NCP to Vernal Equinox: 90° NCP to Summer Solstice: 66.5°
How many galaxies like our own would it take if they were placed edge to edge to reach the nearest galaxy?
Nearest galaxy is about 2.5 million light years away / Milky Way Galaxy has diameter of about 80,000 light years = about 31.25 galaxies
Where would you go on Earth if you wanted to be able to see both the north celestial pole and the south celestial pole at the same time?
Need to stand at Equator
Where would you need to go on Earth to see the celestial equator very near your horizon?
Need to stand at either the North or South Pole
How much of the sky is circumpolar at the equator?
None of it
Solar Day
One Earth rotation with respect to the Sun
Sidereal Day
One Earth rotation with respect to the stars
What is P for Earth? What is A for Earth? Do these values support or disprove Kepler's third law?
P = 1 year (orbital period) A = 1 AU (distance from Sun) Support Kepler's third law
Perigee vs Apogee (Moon's Orbit)
Perigee: close point Apogee: far point
Copernicus model retrograde motion?
Planets go around Sun at different speeds
Nadir
Point directly below your feet
Azimuth
Position angle of an object around the horizon measured with respect to due north (0° to 159°)
Earth's wobble?
Procession
3 Fundamental ways Earth moves through space
Rotation, Revolution, Procession
Autumnal Equinox
September 21; equal day and night
Kepler's 3rd Law... move Earth closer to the Sun?
Shorter orbital period
2 types of day
Solar and Sidereal
How is the solar system different from the galaxy?
Solar system includes the sun and its orbiting planets, while the galaxy contains those solar systems and stars, comets, and asteroids.
What are stars?
Stars are big, self luminous clouds of dust, formed from Hydrogen fusing into Nitrogen.
Why do stars have different colors?
Stars have different colors based on temperature.
What makes stars shine?
Stars shine, or are bright, depending on how much energy they emit.
Sun rising well over to east?
Summer
Heliocentric
Sun centered
What astronomical objects are in the solar system?
Sun, moon, planets, comets, asteroids, dwarf planets
Explain how each of Galileo's telescopic discoveries contradicted the Ptolemaic theory.
Sunspots and lunar craters and mountains challenged the idea that celestial objects are unchanging, perfect orbs. The satellites of Jupiter showed that celestial objects could orbit something besides the Earth. The phases of Venus showed that at least one planet orbited the Sun.
What does the size of the star image in a photograph tell you?
Tells the viewer how bright a star is; Brightness is an indicator for how much energy the stars are emitting, which then hints the star's size
Why do solar eclipses happen only during a new moon? Why not every new moon?
The Earth would be in the Moon's shadow, therefore at the opposite side from the Sun. Do not happen every new moon because the moon's orbit is inclined to Earth's orbit by about 5°.
The "Big Bang" theory refers to the creation of what entity or thing?
The Universe
How is a galaxy different from the universe?
The galaxy is different from the universe because the universe contains everything.
Zenith
The overhead point in the sky
Kepler's 1st Law
The planetary orbits are ellipses, not circles.
When Tycho observed the new star of 1572, he could detect no parallax. Why did that result undermine belief in the Ptolemaic system? In the perfect heavens idea of Aristotle?
The star is further away than the Moon, and so, the heavens are not perfect and unchanging.
Kepler's 2nd Law
The surface area swept out by the planet as it orbits the sun is the same for any time interval.
Moon rising at midnight?
Third Quarter
Today: New Moon. In 21 days?
Third Quarter
Earth's seasons?
Tilt
Tilt at 90°?
Very extreme season
What is the phase of the moon between Full and Last (Third) Quarter?
Waning Gibbous
If the moon is seen at 45° east of the setting Sun, what is its phase?
Waxing Crescent
Tonight you see a waxing crescent moon. Seven days from now, which phase will you see if the night sky is clear?
Waxing Gibbous
How many degrees does Earth move around Sun per day?
about 1°