The Sky, Earth, and Moon; Eclipses Flashcards
Great circle
any circle on the surface of a sphere whose center is at the center of the sphere; ex: Earth’s equator. Same center and circumferences.
Meridian
series of great circles that pass through both the N and S poles; they are perpendicular to the equator, crossing it at right angles. Any point on Earth will have a meridian passing through it (specifies longitude which is 0-180 degrees)
Latitude
the number of degrees of arc you are away from the equator along your meridian (N/S; 0-90 degrees)
What causes the seasons?
Significant variations of heat we receive from the Sun each year which is caused by the 23.5 degree tilt of the Earth’s axis. The axis points in the same direction throughout the year depends on which hemisphere is “leaning” into the sun
Why do daylight hours differ in summer and winter?
Where we see the Sun changes as the year goes on b/c of Earth’s axis, the Sun spends more time where there’s more direct sunlight (longer days) and less time where there’s less direct sunlight (shorter days)
Tropic of Cancer
At 23 degrees north, the Sun is at the zenith at noon on the 1st day of summer
Tropic of Capricorn
At 23 degrees south latitude the Sun passes through the zenith at noon
Arctic Circle
The Sun is as far north on the 1st day of summer; places within 23 degrees of the south pole has sunshine for 24 hours
Antarctic Circle
Places within 23 degrees of the south pole do not see Sun for 24 hours
Vernal and Autumnal
(Spring/Fall; points where the Sun crosses the celestial equator)- Halfway between the solstices every place on Earth receives roughly 12 hours of sunshine and night
Why are all the seasons the same at the equator?
It’s always 12 hours of day and night; determine seasons by the amount of rain
Mean Solar Time
Based on the average value of the solar day over the course of the year (exactly 24 hours; everyday timekeeping); inconvenient for practical use b/c it depends on the position of the Sun, so it’s not strictly observed
Daylight saving time
Local standard time of the place plus 1 hour
International Date Line
Run approximately along the 180 degrees meridian of longitude; runs down the middle of the Pacific Ocean
What makes the moon glow?
The moon glows with reflected sunlight
Phases
Different (planetary) appearances
Lunar Phases
The moon moves completely around the Earth, depending on the angle the Sun makes with the Moon. Moon moves about 12 degrees every day for 30 days= 365 degrees around earth
Waxing (or growing) gibbous
Increase of moons illuminating hemisphere
Sidereal period
The period of the Moon’s revolution about Earth measured with respect to the stars (a little over 27 days). Sidereal month: 27.3217 days
Solar month
The time interval in which the phases repeat from full to full
Synchronous rotation
The moon rotates on its axis at the same time that it takes to revolve about Earth; the Moon always keeps the same face turned toward Earth. The Moon’s appearance is due to a change in illumination, not rotation, so there’s no regular dark side of the moon.
Differential forces
The difference among the forces of the Moon’s attraction on different parts of Earth that cause Earth to distort slightly and stretch slightly into a prolate spheroid with its long diameter pointing towards the moon → tide-raising forces
Spring tides
Tides are greater than normal
Neap tides
Sun produced tides partly cancel the Moon produced tides making them lower than usual
What other factors affect the tides?
Landmasses, friction b/w and in oceans, Earth’s rotation, wind, ocean depth, etc.
How can eclipses occur?
The Sun and Moon have the same angular size of ½ degrees
Solar Eclipse
The Moon and can be seen covering the Sun
Eclipse
It occurs whenever any part of either Earth or the Moon enters the shadow of the other
Lunar Eclipse
When the moon passes into the shadow of Earth and the Moon darkens. The Sun, Earth, and Moon are in a line. Moon is faintly visible being a dull coppery red (illumination is bent as it passes through Earth’s atmosphere)
What determines the duration of an eclipse?
Duration depends on how close the Moon’s path approaches the axis of the shadow
Which eclipse is safe to view?
Lunar eclipse
Umbra
A cone where the shadow is darkest ← the most exciting eclipses
Penumbra
A lighter, more diffuse region of darkness
Total Eclipse
Moon completely covers Sun, occurs when the umbra of the Moon’s shadow reaches the surface of Earth
Corona
The Sun’s outer atmosphere, consisting of sparse gases that extend for millions of miles in all directions from the apparent surface of the Sun
Annular eclipse
Moon cannot cover the Sun completely, therefore a ring of light shows around the Sun
Why can’t eclipses happen all the time?
Eclipses can’t happen all the time because the Moon’s orbit is tilted relative to Earth’s orbit, therefore the Moon is significantly above or below the ecliptic plane to avoid an eclipse. The path of the Earth and moon cross twice a year in the eclipse season.
Eclipse path
The thin zone across Earth within which a total solar eclipse is visible
Describe the visibility of solar and lunar eclipses
A solar eclipse is only visible in certain local areas on Earth, a lunar eclipse is visible to everyone who can see the Moon. Lunar eclipses last longer than solar eclipses
Describe electromagnetic waves
Electromagnetic waves do not require water or air; the fields generate each other and so they can move through a vacuum (outer space)
Aether
A non-existent substance believed to fill all of space so light waves could have something to travel through. proved to be incorrect because waves have no trouble moving through empty space
How fast do EM waves move?
All electromagnetic waves move at the same speed in empty space (the speed of light), which is the fastest possible speed in the universe; origins and properties don’t matter.
What are the characteristics of a wave?
Crests and troughs. Crest to crest is a wavelength
Describe visible light
Can be perceived in different wavelengths through colors (red is longest, violet is shortest)
Frequency
The number of wave cycles that pass by per second (# cycles per second/cps) or hertz (Hz)
How are wavelengths and frequency related?
All electromagnetic waves travel at the same speed
c = λ f
The speed at which a wave moves equal the frequency times the wavelength (c= speed of light)
λ = c/f.
solving for wavelength (c= speed of light)
Describe the propagation of light
Similar to the effects of gravity (force of gravity b/w 2 objects is proportional to the square of their separation). The increase in the area that the light must cover is proportional to the square of the distance that the light has traveled
Inverse-square law for light propagation
The brightness of a source gets weaker with distance
Gamma rays
EM radiation with the shortest wavelengths. Carry a lot of energy and can be dangerous for tissue. Created deep in stars and in violent events of the universe. Can only be studied in space.
X-rays
EM radiation w/ wavelengths b/w 0.01-20 nanometers. More energetic than visible light. Can penetrate soft tissue but not bones. Cannot be used in space b/c Earth’s atmosphere is in the way
Ultraviolet (means higher energy than violet)
Intermediate to X-rays and visible light. Sometimes called black light b/c our eyes can’t see it. Mostly blocked by Earth’s atmosphere, but some come through from the Sun to cause sunburns or skin cancer. This astronomy is best done from space.
Visible light
400-700 nm. Human vision can perceive. Can reach the Earth’s surface.
Infrared (or heat) radiation
b/w visible light and radio waves. Heat lamps mostly radiate this. Our nerve endings are sensitive to this. Absorbed by water and CO2 which are low in Earth’s atmosphere (high mountaintops, high-flying airplanes, and spacecraft)
Microwave
Smaller than radio waves. Absorbed by water vapor, which is great for heating food
Radar waves
A type of radio wave. Used in radar guns and AM radios (1-100s of meters). AM waves are absorbed/reflected by the ionosphere.
What’s the difference between AM waves and FM/TV waves?
AM waves are absorbed/reflected by the ionosphere.
FM and TV waves are not absorbed and can travel easily through the atmosphere
Temperature
The measurement of the average motion of energy of the particles that make it up. Determines the type of EM radiation emitted by dense astronomical objects (Sun, Moon, etc.)
What is responsible for most of the radiation on Earth and in the universe?
The microscopic motion of atoms/molecules (Atoms and molecules moving rapidly= more energetic, higher waves higher frequency)
Blackbody
The relationship b/w temperature and EM radiation. Does not reflect or scatter radiation, but absorbs all EM that falls into it= atoms/molecules vibrate at high speeds. Will radiate EM waves until absorption and radiation are equal. Emits radiation at all wavelengths (all colors) b/c some A/M move faster/slower than others so there’s a broad range of energies and wavelengths. Higher temperature emits more power at all wavelengths than a cooler one. If you add up everything on the EM spectrum you get the total energy emitted by a blackbody
Power
The energy coming off per second (measured in watts)the energy coming off per second (measured in watts)
Wien’s Law
The wavelength at which maximum power is emitted. Wavelength is in nanometers and temperature is in K
Energy flux
The flow of power into an area
Stefan-Boltzmann law
The energy flux from a blackbody at temperature is proportional to the fourth power of iits absolute temperature. F is energy flux, o (sigma) is a constant number
