The Scale of Things, The view from Earth, The Earth-Moon-Sun System Flashcards
Define hypothesis.
Collection of ideas that seem to explain what is observed, predictions that can be tested.
Define Models.
Hypothesis that have withstood observational and experimental tests explain with maths properties and behaviours of some object or phenomenon.
Define Theory.
A set of tested ideas written using math to try explaining how things behave.
Define Laws.
Proven theories that have stood the test of time and have broad applicability.
What did Eratosthenes measure the circumference of the Earth to be in 200 B.C.?
42,000km
What is the actual radius and circumference of Earth?
R: 6371km C: 40,030km
How many times of Earth are the following?
-Moon
-Sun
-Jupiter
-Saturn
4 times smaller
100 times bigger
10 times bigger
9 times bigger
Define A.U.
Astronomical Unit is defined as the average distance between Earth and Sun. Is 1.5 * 10^8 km
Define light year.
Is distance travelled by light in one year. 9.46 * 10^12 km
Define parsec.
Distance at which 1AU perpendicular to the observer’s line of sight subtends an angle of 1 arcsec. 3.09 * 10^13 km
How did aristarchus measure the radius of the sun and the moon.
radius of sun / distance to sun
By calculating the angle between the Sun and the first or third quarter moon to calculate ratio.
radius of moon / distance to moon
From angle we can get distance to moon / distance to sun = 1/400
Hence radius of sun = 400 radius of moon. We have radius of moon.
How many times bigger is the Sun than the moon?
400
How can we calculate the radius of the moon?
By calculating how long it takes the moon to cross Earth’s shadow during a lunar eclipse.
What is the radius of the Moon and of the Sun?
Moon: 1737km
Sun: 696300km
How big is the solar system?
4.5 * 10^9km
T or F. All the planets of the solar system could fit within the radius of the orbit between Earth and the moon theoretically.
True.
What is the speed of light?
3 * 10^8 ms^-1
How long does it take light to travel from the Sun to Earth?
8 minutes
How many stars are in the milky way? How far is the solar system from the centre of the milky way?
10^11 stars
2.8 * 10^4 ly
T or F. If Earth was flat, daytime and nighttime would be equally long throughout the year.
False.
T or F. Daytime / nighttime will happen at the same for everyone on Earth.
True.
How many constellations cover the entire sky?
88
T or F. Stars in a constellation shape are close together.
False.
What angle coverage of the sky is provided by human hand at arms length?
10 degrees.
What is diurnal motion?
The moon, planets and stars follow a similar path in the sky from East to West.
How do we know that the Earth is moving and not the stars?
Foucault’s pendulum
Explain foucault’s pendulum.
A pendulum swings in a fixed plane relative to the stars due to its inertia. Once set in motion, the plane of swing does not rotate by itself. As the Earth rotates, observers on Earth perceive the pendulum’s plane of swing as rotating.
Explain the yearly motion of constellations.
As Earth rotates around the sun, the night sky changes slowly over the course of a year. I.e. There are Summer and Winter constellations.
What is the celestial sphere?
Is an imaginary sphere expanded from the sphere of Earth to contain all the objects in the night sky.
What is the Zenith?
The point directly above an observer on Earth?
What is the significance if the North and South celestial pole?
If in Northern hemisphere, stars inside Northern pole never set, stars inside southern pole never rise. Opposite for southern hemisphere.
What is a circumpolar star?
A star that never sets below the horizon.
How do stars move at?
(a) middle northern latitudes
(b) north pole
(c) the equator
(a) Stars move along paths parallel to the celestial equator.
(b) The celestial equator lies all around you at the horizon. Stars move horizontal
(c) The celestial equator is a semicircle passing directly overhead, stars move vertically.
How do circumpolar stars change?
The rotation axis of Earth is slowly moving with time. This is called precession.
(Imagine spinning top, fixed in place at an angle, the direction it points toward changes as it rotates)
What is the angle of declination?
Angular distance north or south from the celestial equator.
What is the angle of right ascension?
Angular distance from the vernal equinox eastward along the celestial equator up to the circle used to measure its declination.
What is the sidereal day?
Time it takes for Earth to complete a full rotation. 360 degrees.
What is the solar day?
Time it takes for Earth to rotate about its axis so the Sun appears in the same position.
T or F. The sideral day is longer than the solar day.
False.
What is the ecliptic plane?
Plane of Earth’s orbit around the Sun.
From our point of view, what is the ecliptic?
Apparent path of the Sun around the celestial sphere.
Why are there seasons?
23.5 degrees tilt of the Earth
T or F. The tilt of the Earth is always 23.5 degrees.
False, it wobbles between extreme values.
Why is Summer hotter?
Sun is higher in the sky so shaft in sunlight is more concentrated onto a small area, which heats the ground effectively.
What are equinoxes?
Points on the ecliptic where the celestial equator and the ecliptic intersect. I.e. The earth is not angled toward the sun.
What are solstices?
Points on the ecliptic farthest north (Sun highest longest days) and farthest south (Sun lowest shortest days).
What is the dark side of the moon?
Because the rotation of the Moon is synchronized with its orbit around Earth we only ever see one side of the Moon. It is not actually dark.
What is the sidereal month?
Time it takes the Moon to complete one full orbit around Earth.
What is the synodic month?
Time it takes the Moon to complete one cycle of phases.
T or F. The synodic month is longer than the sideral month.
True
Why does an eclipse not occur every time the moon passes between the sun and Earth?
The plane of the moon’s orbit of the earth is at a 5 degree tilt to the earth’s orbit of the sun.
What is a lunar eclipse?
Earth comes between sun and moon. The Earth casts a shadow on the Moon.
Why does the moon appear red during a lunar eclipse?
The colour red on the Moon is due to Earth’s atmosphere which scatters blue light.
Difference between penumbra and umbra.
Penumbra leads to partial eclipse.
Umbra leads to total eclipse.
What is a solar eclipse?
The moon comes between the sun and the Earth. Totality is only seen on a small portion of the Earth.
Differentiate between an annular and a total eclipse.
Annular: Moon is farther away and not as big, the moon can’t completely cover the sun even in the umbra.
Total: Moon is closer and bigger, the moon completely cover’s the sun apart from the corona in the umbra.
T or F. The existance of solar and sideral days proves the Earth obits the Sun.
False.
T or F. At the equinox, the sun rises in the East and sets in the West.
True.
T or F. In Summer times in the Northern hemisphere, the sun rises from the North East and sets in the North West.
True.
T or F. In Winter times in the Northern hemisphere, the sun rises from the South East and sets in the South West.
True.
T or F. During equinoxes, night and day are almost the same everywhere.
True.
At what times does the full moon rise?
At sunset.
If you see the moon with the right-side lit up in the Northern hemisphere is the moon increasing or decreasing.
Increasing.
How can you tell the difference between the two eclipses?
lunar = moon being hid
solar = sun being hid
A minute of arc is what?
one-sixtieth of a degree
T or F. Without travelling to space, you can prove that Earth is round and rotates around its own axis
True
T or F. The sky is divided in 88 equal in size regions known as constellations
False.
T or F. All the stars that we can see in the night sky without using telescopes are located at relatively small distances to us within the Milky Way (our galaxy)
True.
T or F. The declination of a star is equivalent to its altitude over the horizon
False.
declination of a star is a fixed value on celestial sphere.
If the Moon as seen from Earth is in the waning crescent phase, what Earth phase would be seen from the near side of the Moon?
Waxing gibbous
T or F. Total lunar eclipses last longer than total solar eclipses
False.
If you were on the Moon and continued to stand at the same location,
the daytime sky would be blue, and sunset would occur approximately every 30 days
the daytime sky would be black, and sunset would occur approximately every 24 hours
the datytime sky would be blue, and sunset would occur approximately every 24 hours
sunset would never occur because half of the Moon is always bright and the other half is always dark
the daytime sky would be black, and sunset would occur approximately every 30 days
the daytime sky would be black, and sunset would occur approximately every 30 days
When are the equinoxes?
Spring March 20th
Autumn September 22nd
What is the highest declination of the Sun?
23.5 degrees
What are the units of right ascension?
hours, minutes, seconds.
DEGREES NOT USED!
T or F. Constellations whose stars are circumpolar can be seen throughout the year unlike seasonal constellations.
True.
T or F. At a given time, a total lunar eclipse is visible only from a small part of Earth’s surface
False.
T or F. At mid-norther latitudes, the full moon passes higher in the sky in Winter than in Summer.
True.
On the first day of spring, in Ireland, the Sun rises?
north of east
If the Moon orbited Earth twice as fast but in the same orbe the frequency of solar eclipses would
stay the same
