Sun-Earth Relationships Flashcards
In astronomy, what is the unit we use for distance?
light year
Describe a light-year:
Light-year: distance that light travels at one-year
What is the speed of light?
light speed: 300,000 km/s
How many light-years in the Milky Way?
The Milky Way is 100,000 light-years across
True or False: A light year is a measurement of time.
False, Light year is a unit of distance!!!
Where is our solar system found in the galaxy?
The edge of our solar system is found beyond Neptune’s orbit, found in the Orion Spur of the Sagittarius Arm.
How long does it take for the light from the sun to reach earth?
Light reaches Earth from the Sun in about 8 minutes and 20 seconds.
True or False: when we look up at the sun, what we are seeing is the past sun
True.
Is earths orbit circular or oval?
Oval, AKA elliptical.
There is a time of year when the earth is closest to the sun,___________, and the time of year when the earth is farthest from the sun, ___________.
(perihelion), (aphelion).
Average distance from Earth to the Sun is ___________ km
150,000,000
______________: where the earth is closest to the sun January 3 147,255,000 km.
Perihelion
___________: where the earth is farthest from the sun July 4 152,083,000 km
Aphelion
What is the name of the plane of Earth’s orbit around the Sun?
Plane of the Ecliptic.
What is the distance and date of Perihelion?
147,255,000 km, January 3.
What is the distance and date of Aphelion?
152,083,000 km, July 4.
____________: At all times in orbit, the Earth’s polar axis is parallel to itself.
axial parallelism
Why is the North Star is always (essentially) directly overhead at the North Pole, always pointing in the same direction?
Because the Axial Parallelism.
Every 100,000 years, the orbit becomes more elliptical and changes shape.
Eccentricity
What is the Sub-solar Point?
Point on Earth’s surface with Sun directly overhead.
Describe how you would find the Subsolar Point:
The sun’s rays hitting perpendicular, 90 degrees between the surface of the earth and the ray from the sun, we look at the latitude where it hits earth at that point.
What is Declination?
The angle north or south from the equator measured along a great circle passing through the pole.
Define Declination, in short:
The latitude of the subsolar point.
What is the range of Declination?
-23.5 to + 23.5 degrees. N/S
Declination is positive when subsolar point is _____ of the equator, and negative When it is ____ of the equator.
north, south
What is declination reliant on?
This depends on how the axis is tilted relative to the plane of the ecliptic.
True or False: For any location, the declination refers to the position of the sun in the sky throughout the day and, therefore, the amount and intensity of sunlight received.
True.
What is Insolation, in short?
Incoming solar radiation.
Define Insolation:
The total amount of sunlight (solar radiation) received at some point on the surface of the earth, on any (24 hour) day.
What three things determine Insolation?
-The decline of the angle of the sun in reference to earth’s equator.
-The latitude.
-The amount of sunlight blocked/reduced/diminished (attenuated) by clouds, aerosols, gases, etc.
True or False: If we ignore the presence of the atmosphere, or assume that there is no atmosphere, or assume that we are calculating the Incoming Solar Radiation (INSOLATION) at the top of the atmosphere (above the gases etc.), we only must consider declination and latitude.
True.
True or False: Declination is determined by the month of the year.
False, it is determined by the day of the year.
-The earth’s axial tilt (obliquity) with respect to the plane of the ecliptic.
There are four critical dates throughout the year that best illustrate how and why insolation varies throughout the year and by ________.
latitude
What four critical dates throughout the year that best illustrate how and why insolation varies throughout the year and by latitude?
-Winter Solstice
-Summer Solstice
-Vernal Equinox
-Autumnal Equinox
When is the Winter Solstice?
December; ‘Winter Solstice’–approx. Dec.21, Like parhelion and aphelion.
When is the Summer Solstice?
June; ‘Summer Solstice’-approx. June 21, Like parhelion and aphelion.
When is the Vernal Equinox?
-March ‘Vernal’ Equinox- approx. March 20.
When is the Autumnal Equinox?
September ‘Autumnal’ Equinox- approx. Sept. 22
What is the declination on the winter solstice?
declination= -23.5 degrees.
-The axis is tiled –23.5 degrees away from the sun, relative to the plane of the ecliptic.
What is the subsolar point during the winter solstice?
-Subsolar point is at 23.5 degrees S (the Tropic of Capricorn).
December solstice: _________ sunlight north of the arctic circle, 66.5 degrees __ (photoperiod= ___hours).
No direct, North, and zero.
Winter Solstice: _____ of sunlight south of the Antarctic circle, 66.5 degrees __ (photoperiod= ___ hours).
24 hours, south, and 24.
What is the declination for the June Solstice?
Declination = +23.5 degrees. Northern hemisphere is tilted towards the sun, Opposite of the winter solstice.
what is the subsolar point during the summer solstice?
Subsolar point is at 23.5 degrees N (the Tropic of Cancer).
Summer Solstice: _____ sunlight south of the Antarctic Circle, 66.5 degrees ___ (photoperiod= ___hours).
No direct, south, zero.
Summer Solstice: _______ of sunlight north of Arctic Circle, 66.5 degrees ___ (photoperiod = ___ hours).
24 hours, north, 24.
What is the declination during the Equinoxes?
Declination = 0 degrees.
Why is the declination zero degrees during the equinoxes?
This is because the plane of the ecliptic is aligned with the subsolar point, all lined to 0 degrees.
True or False: During an equinox, all places on earth have essentially equal day and night, approximately, 12-hour photoperiods everywhere, and the sun rises directly in east everywhere, sun sets directly in west everywhere.
True.
Why is it important to know why the sun moves across the sky throughout the year, throughout the day, and at all latitudes?
Because Sunlight is the energy that drives the climate system, and fuels life on earth.
Define the sun’s altitude:
the angle of the horizon and the sun) varies by; time of day, date of year, and latitude.
_________ regions have a large variation in seasons.
Mid-latitudes
True or False: Seasonality dictates how much solar energy a given location receives throughout the year.
True.
What are the five reasons for seasons?
-Revolution
-Rotation
-Tilt (Obliquity) of Earth’s Axis
-Axial Parallelism
-Sphericity (the shape of the earth)
Define Revolution in terms of the earth:
Earth revolves around the sun; voyage takes one year 356.2422 days
Define Rotation in terms of the earth:
Earth rotates on its axis once every 24 hours.
Define the Tilt of Earth’s Axis (Obliquity):
Axis is tiled 23.5 degrees from plane of ecliptic.
Define Axial Parallelism:
Axis maintains alignment during orbit of the sun. The North pole points towards the north star (Pollaris).
Define Sphericity:
Because the earth is roughly a sphere (geoid), the sun’s rays are diffused, or spread out, when not directly overhead. Picture the surface area of half a sphere vs. That of a flat circle of the same diameter.
How many stars are in the Milky Way? (roughly)
400 Billion
