The Hydrosphere – includes all the
water found on Earth (Lakes, ponds, oceans ice caps and even water
vapour in the air. All organisms depend on water for their
metabolism; most chemical reactions take place in water. (Hydro
means water in Greek.)
The Atmosphere – the envelope of air
that surrounds the Earth. It is often subdivided into four zones
(called from lowest altitude to highest:
Layers of the Earth's Atmosphere:
- The Troposphere;
- Stratosphere and Ozone Layer; - Mesosphere and Ionosphere
- Thermosphere and Exosphere (Atmos
means air or vapour in Greek.)
The Lithosphere – the outermost solid layer of Earth,
its crust and upper mantle. It is made of the large mobile plates we
studied in geology both land masses and under the ocean floor. In
this topic we will be most interested in the rock and soil types.
(Litho means rock in Greek.)
These entire three systems link together to form a Biosphere, a
region that supports living things (or biota.) It is common to
subdivide the Biosphere into regions characterized by their main
These regions called Biomes include deserts, tundra, tropical
rainforest, savannah, and alpine areas
describes the way organisms are found together in a physical place.
Both physical (abiotic) and biological (biotic) factors describe an
ecosystem. Examples of abiotic factors may be: wind speed, humidity,
rainfall, soil type, air temperature etc. While biotic factors may
include the presence of producers, parasites, competitors, pathogens
and decomposers in the community
Earth The Power Of The Planet - Atmosphere ( 59 mins)
Presented by Dr Iain Stewart
The atmosphere is Earths protective layer, cloaking
us in a warm, oxygen-rich embrace and shielding us from the cold
hostility of space. Its immensely powerful but at the same time
highly sensitive. Its destructive, yet it shelters us.
Introduction to Water ( 3 mins)
This is a 4 minute dramatic video choreographed to
powerful music, which introduces the viewer to the wonder and
miracle of water. It is designed as a motivational "trailer" to be
shown by Biology, Biochemistry and Life Science teachers in middle
and high school and college as a visual "Introduction" to this
amazing substance, and its use by life on Earth. As a high school
Biology teacher myself, I have found this video to truly inspire my
students to want to learn more about the topic.
Properties Of Water ( 4:36 mins)
The physical nature of water. A short video made for
the UMass Botany for Gardeners class.
Water Cycle Video ( 3 mins)
Antarctic Ice Cap
Ice Caps and Glaciers
Storehouses of freshwater
Earth The Power Of The Planet – Ice ( 58 mins)
Earth's Air Currents & Jet Stream
Air and Ocean Currents
Earth's Ocean Currents
Our Dynamic Planet
The Sun, Moon,
planets and stars might ultimately control Earth’s atmosphere and
Earth is NOT an isolated ball, statically situated in
a completely vacuous space. - It is an active, elastic sphere
moving through a cosmic environment rich in astronomical energies.-
Its atmosphere is a thin, fluid envelope encircling and interacting
with a more densely fluid, liquid covering (the oceans). Beyond
these terrestrial fluid features, fluid-like cosmic plasma ebbs and
flows between the planets and sun, and between the expanses of
interstellar space where spectacular events shape all reality, as we
Ocean Temperature Variations
between Solar Cycles
Ocean Temperature Maps
El Niño and La Niña - and
the Solar Cycles
Cycle Triggers La Nina, El Nino-like Climate Shifts
Researchers have discovered a link between the 11-year solar cycle
and tropical Pacific weather patterns that resemble La Niña and El
Solar Activity Controls El Niño
and La Niña
El Nino/La Nina Explainer ( 8 mins)
El Niño and La Niña - Maps by Years (
El Niño & the Warm Waters of the
( 4 mins)
El Nino is marked by the
appearance from time to time of warm water in the central and
eastern Pacific Ocean. The end result of the evaporative process
that follows is excessive rainfall.
Forcing by Earth-Moon-Sun
Recession of the Moon & Earth’s Tidal
As the moon orbits the earth, its gravity pulls on the earth’s
oceans, causing tides. Since the earth rotates faster than the moon
orbits, the tidal bulges induced by the moon are always “ahead” of
the moon. For this reason the tides actually “pull forward” on the
moon, which causes the moon to gain energy and gradually spiral
outward. The moon moves about an inch and a half farther away from
the earth every year due to this tidal interaction. Thus, the moon
would have been closer to the earth in the past.
Six thousand years ago, the moon would have been about 800 feet (250
m) closer to the earth (which is not much of a change considering
the moon is nearly a quarter of a million miles, or 400,000 km,
away). So this “spiraling away” of the moon is not a problem over
the biblical time scale of 6,000 years, but if the earth and moon
were over 4,000,000,000 years old (as big-bang supporters teach),
then we would have big problems. This is because the moon would have
been so close that it would actually have been touching the earth
less than 1.5 billion years ago. This suggests that the moon can’t
possibly be as old as secular astronomers claim.
Secular astronomers who assume the big bang is true must invoke
other explanations to get around this. For example, they might
assume that the rate at which the moon was receding was actually
smaller in the past (for whatever reason), but this is an extra
assumption needed to make their billions-of-years model work.
The simplest explanation is that the moon hasn’t been around for
that long. The recession of the moon is a problem for a belief in
billions of years, but is perfectly consistent with a young age.
Aquarius Yields NASA'S First Global Map Of Ocean
NASA's new Aquarius instrument has produced its first
global map of the salinity of the ocean surface, providing an early
glimpse of the mission's anticipated discoveries.
Aquarius, which is aboard the Aquarius/SAC-D (Satelite de
Aplicaciones Cientificas) observatory, is making NASA's first space
observations of ocean surface salinity variations - a key component
of Earth's climate. Salinity changes are linked to the cycling of
freshwater around the planet and influence ocean circulation.
"Aquarius' salinity data are showing much higher quality than we
expected to see this early in the mission," said Aquarius principal
investigator Gary Lagerloef of Earth & Space Research in Seattle.
"Aquarius soon will allow scientists to explore the connections
between global rainfall, ocean currents and climate variations." …
NASA Perpetual Ocean (1080p HD) ( 3
This visualization shows ocean surface currents around the world
during the period from June 2005 through December 2007. The goal was
to use ocean flow data to create a simple, visceral experience.
This visualization was produced using NASA/JPL's computational model
called Estimating the Circulation and Climate of the Ocean, Phase II
or ECCO2.. ECCO2 is high resolution model of the global ocean and
sea-ice. ECCO2 attempts to model the oceans and sea ice to
increasingly accurate resolutions that begin to resolve ocean eddies
and other narrow-current systems which transport heat and carbon in
the oceans.The ECCO2 model simulates ocean flows at all depths, but
only surface flows are used in this visualization. The dark patterns
under the ocean represent the undersea bathymetry. Topographic land
exaggeration is 20x and bathymetric exaggeration is 40x.
Ozone Color Chart over Antarctica
Ozone Color Chart over Antarctica
Ozone (O3) high in the atmosphere absorbs ultraviolet
radiation from the sun, thereby protecting living organisms below
from this dangerous radiation. The term ‘ozone hole’ refers to
recent depletion of this protective layer over Earth's polar
regions. People, plants, and animals living under the ozone hole are
harmed by the solar radiation now reaching the Earth's surface—where
it causes health problems from eye damage to skin cancer.
The ozone hole, however, is not the mechanism of global warming.
Ultraviolet radiation represents less than one percent of the energy
from the sun—not enough to be the cause of the excess heat from
human activities. Global warming is caused primarily from putting
too much carbon into the atmosphere when coal, gas, and oil are
burned to generate electricity or to run our cars. These gases
spread around the planet like a blanket, capturing the solar heat
that would otherwise be radiated out into space. (For more detail on
the basic mechanism of global warming, see carbon dioxide FAQ.)
Night fly by ISS
Aurora australis (11
September 2005) as captured by NASA's IMAGE satellite, digitally
overlaid onto The Blue Marble composite image.
Image from Space
An Introduction to Auroras
Does the Aurora occur on other Planets?
The answer is yes! - The Earth is not the only planet
in the solar system on which auroras may be seen. Auroras may also
be seen on the gas giants, Jupiter, Saturn, Uranus and Neptune.
These planets all have strong magnetic fields and vast atmospheres.
These images taken by the Hubble Space Telescope, show the aurora at
Jupiter. These auroras happen for the same reason as on Earth. The
gases in the upper atmosphere are excited by charged particles
pouring in near the north and south magnetic poles. Most of the
particles come from the solar wind but some flow from Jupiter's
nearest moon, Io, and are trapped by the magnetic field. (NASA
LINK to our Auroras and Double Rainbows Page
LINK to our PAGE:
Earth Magnetic Field
Reversal & The Magnetosphere
The Inner and Outer Van Allen
The Van Allen Radiation Belt
The Van Allen radiation belt is composed
of two torus-shaped layers of energetic charged particles (plasma)
around the planet Earth, held in place by its magnetic field. The
belt extends from an altitude of about 1,000 to 60,000 kilometers
above the surface, in which region radiation levels vary. It is
thought that most of the particles that form the belts come from
solar wind, and other particles by cosmic rays. It is named after
its discoverer, James Van Allen, and is located in the inner region
of the Earth's magnetosphere. It is split into two distinct belts,
with energetic electrons forming the outer belt and a combination of
protons and electrons forming the inner belt. In addition, the
radiation belts contain lesser amounts of other nuclei, such as
alpha particles. The belts pose a hazard to satellites, which must
protect their sensitive components with adequate shielding if their
orbit spends significant time in the radiation belts.
The existence of the belt was confirmed
by the Explorer 1 and Explorer 3 missions in early 1958, under Dr.
James Van Allen at the University of Iowa. The trapped radiation was
first mapped out by Explorer 4, Pioneer 3 and Luna 1.
The term Van Allen belts refers specifically to the radiation belts
surrounding Earth; however, similar radiation belts have been
discovered around other planets. The Earth's atmosphere limits the
belts' particles to regions above 200–1,000 km, while the belts
do not extend past 7 Earth radii RE.The belts are confined to a
volume which extends about 65° from the celestial equator.
for Space Travel
Missions beyond low earth orbit leave the protection of the
geomagnetic field, and transit the Van Allen belts. Thus they may
need to be shielded against exposure to cosmic rays, Van Allen
radiation, or solar flares. The region between two to four earth
radii lies between the two radiation belts and is sometimes referred
to as the "safe zone"....
Radiation Belts Surprisingly Dynamic, New Probes Find
NASA probes spots temporary third
Van Allen radiation belt
For over fifty years schoolbooks have
been teaching about the Van Allen belts, two torus-shaped zones of
charged particles that encircle the Earth. Now, a NASA mission has
discovered that there is a third – but only when conditions are
Van Allen Radiation Belts to be Explored
by New Spacecraft | NASA RBSP Storm Probe Mission Video ( 3
the Radiation Belt Storm Probe (RBSP)
mission will explore Earth's Van Allen Radiation Belts. The protons,
ions, and electrons in these belts can be hazardous to both
spacecraft and astronauts
Radiation Belt Probes to Add to
Understanding of Space Weather
Space weather events can significantly affect the Van Allen Belts
and GNSS signals.
Lightning travels at over 100
Lightning from the Ground up
Wind turbines are silhouetted by
lightning in Jacobsdorf, in Brandenburg, Germany
Lightning & lightning storms -
one of the most unpredictable
forces of nature.
- They Occur high
on top of thunderstorm Clouds &
as luminous white - bluish or
Lightning is a massive electrostatic
discharge caused by unbalanced electric charge in the
atmosphere, either inside clouds, cloud to cloud or cloud to ground,
accompanied by the loud sound of thunder.
Sound of a thunderstorm
A typical cloud to ground lightning strike can be over 5 km (3 mi)
long. A typical thunderstorm may have three or more strikes per
minute at its peak. Lightning is usually produced by cumulonimbus
clouds up to 15 km high (10 mi) high, based 5-6 km (3-4 mi) above
the ground. Lightning is caused by the circulation of warm
moisture-filled air through electric fields. Ice or water particles
then accumulate charge as in a Van de Graaf generator. Lightning
may occur during snow storms (thundersnow), volcanic eruptions, dust
storms, forest fires or tornadoes. Hurricanes typically generate
some lightning, mainly in the rainbands as much as 160 km (100 mi)
from the center.
When the local electric field exceeds the dielectric strength of
damp air (about 3 million Volts/m), electrical discharge results,
often followed by more discharges along the same path. Mechanisms
that cause lightning are still a matter of scientific investigation.
The study or science of lightning is
Lightning Sprites are
large-scale electrical discharges that occur high above thunderstorm
clouds, or cumulonimbus, giving rise to a quite varied range of
visual shapes flickering in the night sky. They are triggered by the
discharges of positive lightning between an underlying thundercloud
and the ground.
Sprites appear as luminous reddish-orange flashes.
Lightning & Sprites ( 10 mins)
Film done with a High Speed Camera and
shown in slow-motion from high altitude flights !!!
( see also the Aurora Page from
ISS- Intl Space Station video on Lightnings and Auroras )
Lightning Types and Classifications
- Some are:
Cloud-to-cloud, Ground Up;
Anvil Crawlers; Sprites and Jets; Ball Lightning; Heat Lightning
How to photograph Lightning at night
Lightning by the Shore
Lightning near a Tornado
Many Lightning Images>
Eratosthenes' measurement of the
276 BC - 194 BC
Eratosthenes Method- Axial Tilt & Seasons
Eratosthenes Method - Earth
Circumference measure… Prime numbers & first to noticed that the
Earth was tilted and we get the seasons…
Eratosthenes of Cyrene (Ancient Greek: c. 276 BC – c. 195 BC)
was a Greek mathematician, geographer, poet, athlete, astronomer,
and music theorist.
He was the first person to use the word "Geography" and invented the
discipline of geography as we understand it. He invented a system of
Latitude and Longitude.
He was the first person to calculate the circumference of the earth
by using a measuring system using stades, or the length of stadiums
during that time period (with remarkable accuracy). He was the first
to calculate the tilt of the Earth's axis (also with remarkable
accuracy). He may also have accurately calculated the distance from
the earth to the sun and invented the leap day. He also created the
first map of the world incorporating parallels and meridians within
his cartographic depictions based on the available geographical
knowledge of the era. In addition, Eratosthenes was the founder of
scientific chronology; he endeavored to fix the dates of the chief
literary and political events from the conquest of Troy
Using shadows to measure the World
measured the tilt of the Earth axis by 23.5 degrees, which gives us
the seasons .
Earth's rotation period relative to the Sun—its mean solar day—is
86,400 seconds of mean solar time (86,400.0025 SI seconds). As
the Earth's solar day is now slightly longer than it was during the
19th century because of tidal acceleration, each day varies between
0 and 2 SI ms longer…
Earth Rotating - 24 Hours
a Day - Tilting is Creating our Seasons ( 3 mins)
Earth Seasons ( 1:27 mins)
the reason behind seasonal changes on Earth due to tilting earth
axis by 23.5 degree with the equator.
In Islamic astronomy, Khujandi worked under the patronage of the
Buwayhid Amirs at the observatory near Ray, Iran, where he is known
to have constructed the first huge mural sextant in 994 AD.
Al-Khujandi determined the axial tilt to be 23°32'19" (23.53°) for
the year 994 AD.
Why Does The Earth Spin?
The Earth spins on its axis, completing
a full revolution every day. By why does it do this? One of the most
common misconceptions in physics is the belief that constant motion
requires a constant force. So many people believe there must be some
force in the Earth (e.g. gravity, centrifugal force) that keeps it
spinning. In truth, no force is required because a fundamental
property of mass is that it maintains its state of motion in the
absence of external forces. This property is called "inertia".
Latitude & Longitude
Prime Meridian GMT England
GMT Monument - East/West Meridians
Monument - North/South
Latitude & Longitude & Greenwich Mean Time
Do you remember learning
about how to measure latitude and longitude? On the Earth,
measures how far north or
south a place is from the Equator. For example, France is at about
45 degrees ( o) north. It is halfway between the Equator and the
North Pole. The Equator is at 0o (neither north nor south), and the
North Pole is at 90o north. At what latitude is your state or
Look at the
Degrees Latitude diagram. This diagram illustrates how degrees of
latitude are measured in the galactic coordinate system. The
galactic plane is like the Equator. It is at 0o latitude. The Earth
is on the galactic plane. It is also at 0o latitude.
Mean Time (GMT)
Measuring Latitude by Polaris
( 8 mins)
Ecuator - 0 Deg. - The
Tropics & Arctic Circles...
Is The Earth is Growing ? - Or is
the Pangea Theory more close to the Truth ?? ( 10 mins)
Ocean Floor ??
The Earth’s Moon
Orbit of the Moon
The Moon completes its orbit around the Earth in approximately 27.3
days (a sidereal month). The Earth and Moon orbit about their
barycentre (common centre of mass), which lies about 4600 km from
Earth's centre (about three quarters of the Earth's radius). On
average, the Moon is at a distance of about 385000 km from the
centre of the Earth, which corresponds to about 60 Earth radii. With
a mean orbital velocity of 1,023 m/s, the Moon moves relative to the
stars each hour by an amount roughly equal to its angular diameter,
or by about 0.5°. The Moon differs from most satellites of other
planets in that its orbit is close to the plane of the ecliptic, and
not to the Earth's equatorial plane. The lunar orbit plane is
inclined to the ecliptic by about 5.1°, whereas the Moon's spin axis
is inclined by only 1.5°
What Is the Shape of the
it takes 27.3 days for the moon to orbit Earth in counterclockwise
rotation. The unique elliptical shape of the lunar orbit affects its
apparent size, its velocity and other factors of its relationship to
The moon's orbit is distinctly elliptical, with the Earth at one
focus. This is in agreement with Kepler's laws of planetary motion,
which state that all orbits are elliptical. Orbits vary from being
slightly different from circles to being distinctly ovate. The moon
has an eccentricity of 0.0549, which is the ratio of the distance
between the foci of the ellipse and the longest axis of the ellipse.
Because of its elliptical orbit, the moon's distance from the Earth
varies by thirteen percent as it travels around us. Its apparent
size changes as it moves closer to, or further from, the Earth. The
elliptical orbit also creates variations in the angular speed of the
moon as it approaches Earth.
Perigee and Apogee
Perigee refers to the closest distance between the Earth and the
moon, which is 7 percent less than the average lunar distance from
Earth. When the moon is at apogee it is farthest from Earth, about
six percent more than average.
The lunar orbit is tilted 5.145° when compared to the orbital plane
of the Earth around the Sun. The slight tilt, or inclination, adds
the effect of the Sun's gravity on the lunar orbit, causing the
moon's path over the stars to change slightly each month. It also
causes slight changes in the shape of the moon's orbit every year.
In the course of rotation the moon's apparent shape changes
dramatically as it moves through its lunar phases, which are caused
by the shadow of the Earth. However, the same face of the moon is
always turned toward the Earth; this is called synchronous rotation,
in which the moon rotates once for its every orbit of the Earth.
Earth's Moon Maps - National Geographic
Earth's moon is tilted 5 degrees
plane of the solar system.
Moon Orbits Earth
Phases: Rising and Setting
Distance from Moon to Earth
The Moon orbiting Earth with
sizes and distances to scale.
Halos around the moon – or sun –
are a sign of thin cirrus clouds drifting high above our heads. They
are a sign of
Moon Halo with a Rainbow
A halo (from Greek ἅλως; also known as a
nimbus, icebow or gloriole) is an optical phenomenon produced by ice
crystals creating colored or white arcs and spots in the sky. Many
are near the sun or moon but others are elsewhere and even in the
opposite part of the sky. They can also form around artificial
lights in very cold weather when ice crystals called diamond dust
are floating in the nearby air.
There are many types of ice halos. They are produced by the ice
crystals in cirrus clouds high (5–10 km, or 3–6 miles) in the upper
troposphere. The particular shape and orientation of the crystals is
responsible for the type of halo observed. Light is reflected and
refracted by the ice crystals and may split up into colors because
of dispersion. The crystals behave like prisms and mirrors,
refracting and reflecting sunlight between their faces, sending
shafts of light in particular directions.
makes a halo around the sun or moon?
Link to our Sun's and Moon's Halos Page
We travel nearly 67,000 miles per
hour in our yearly orbit around the sun.
Circular orbit, no eccentricity.
Orbit with 0.5 eccentricity.
Earth’s Orbit Around the Sun
Spinning is just one of Earth’s several motions. We’re also orbiting
the sun at 18.5 miles per second or nearly 67,000 miles per hour. At
that speed our planet traverses 600 million miles in one year. Since
Earth’s about 8,000 miles in diameter, it moves about 202 times its
own size in one day. Even sitting still we’re putting on miles at a
fantastic rate. Live till you’re 80 years old and you’ll have 48
billion frequent orbital-flyer miles to show for it.
The Earth's Orbit around the
Sun has many interesting Characteristics.
The Earth’s orbit around the Sun has many interesting
characteristics. First, the speed of our orbit is 108,000 km/h. The
planet travels 940 million km during one orbit. The Earth completes
one orbit every 365.242199 mean solar days(that might help explain
the need for a leap year). The planet’s distance from the Sun varies
as it orbits. Actually, the Earth is never the same distance from
the Sun from day to day. When the Earth is closest to the Sun it is
said to be at perihelion. This occurs around January 3rd at a
distance of 147,098,074 km. When it is at its furthest distance from
the Sun, Earth is said to be at aphelion. That happens around July
4th at a distance of 152,097,701 km.
The seasons are caused by a combination of two factor: the Earth’s
axial tilt and its distance from the Sun during the orbital period.
The planet is tilted 23.4° offset of the axis from a direction
perpendicular to the Earth’s orbital plane. This puts a different
hemisphere towards the Sun at different times of the year. When the
Earth is at a certain place in its orbit, the northern hemisphere is
tilted toward the Sun and experiences summer. Six months later, when
the Earth is on the opposite side of the Sun, the northern
hemisphere is tilted away from the Sun and experiences winter.
The shape of Earth’s orbit isn’t quite a perfect circle. It is more
like a “stretched out” circle or an oval. Mathematicians and
astronomers call this shape an “ellipse”. An ellipse can be long and
skinny or it can be very round. Scientists need a way to describe
how round or “stretched out” an ellipse is. They use a number to
describe this, and call it the eccentricity of the ellipse.
Eccentricity is always between zero and one for an ellipse. If it is
close to zero, the ellipse is nearly a circle. If it is close to
one, the ellipse is long and skinny. Earth’s orbit is almost a
circle, it has an eccentricity of less than 0.02. That is why the
distance from the Sun at perihelion and aphelion are very close.
The Shape of Earth's Orbit
Animation showing a change in the Earth's orbital shape.
The most important orbital change studied by Milankovich is the
change in the shape of the Earth's orbit from nearly circular to
slightly elongate and back again. The time it takes to go through a
complete cycle from circular to elongate and back to circular is
about 100,000 years.
During the portion of the shape change cycle when the orbit is
nearly circular, the Earth-Sun distance is nearly the same for all
parts of the orbit, making the Earth's average temperature the same
all year round. As the orbit becomes more elongate, the Earth orbits
slightly farther from the Sun at aphelion and slightly closer at
perihelion, making the average temperature slightly lower at
aphelion and slightly higher six months later at perihelion. Also,
since the Earth moves more slowly near aphelion, when the orbit is
elongated, the time during which the temperatures are lower lasts
Milankovitch theory describes the collective effects of changes in
the Earth's movements upon its climate, named after Serbian
geophysicist and astronomer Milutin Milanković, who worked on it
during First World War internment. Milanković mathematically
theorized that variations in eccentricity, axial tilt, and
precession of the Earth's orbit determined climatic patterns on
Earth through orbital forcing.
The Earth's axis completes one full cycle of precession
approximately every 26,000 years. At the same time the elliptical
orbit rotates more slowly. The combined effect of the two
precessions leads to a 21,000-year period between the astronomical
seasons and the orbit. In addition, the angle between Earth's
rotational axis and the normal to the plane of its orbit (obliquity)
oscillates between 22.1 and 24.5 degrees on a 41,000-year cycle. It
is currently 23.44 degrees and decreasing.
Orbital shape (Eccentricity)
The Earth's orbit is an ellipse. The eccentricity is a measure of
the departure of this ellipse from circularity. The shape of the
Earth's orbit varies in time between nearly circular (low
eccentricity of 0.005) and mildly elliptical (high eccentricity of
0.058) with the mean eccentricity of 0.028. The major component of
these variations occurs on a period of 413,000 years (eccentricity
variation of ±0.012). A number of other terms vary between
components 95,000 and 125,000 years (with a beat period 400,000
years), and loosely combine into a 100,000-year cycle (variation of
−0.03 to +0.02). The present eccentricity is 0.017.
If the Earth were the only planet orbiting our Sun, the eccentricity
of its orbit would not perceptibly vary even over a period of a
million years. The Earth's eccentricity varies primarily due to
interactions with the gravitational fields of Jupiter and Saturn. As
the eccentricity of the orbit evolves, the semi-major axis of the
orbital ellipse remains unchanged. From the perspective of the
perturbation theory used in celestial mechanics to compute the
evolution of the orbit, the semi-major axis is an adiabatic
invariant. According to Kepler's third law the period of the orbit
is determined by the semi-major axis. It follows that the Earth's
orbital period, the length of a sidereal year, also remains
unchanged as the orbit evolves. As the semi-minor axis is decreased
with the eccentricity increase, the seasonal changes increase. But
the mean solar irradiation for the planet changes only slightly for
small eccentricity, due to Kepler's second law…
Guide to the Equinoxes and Solstices
Seeing Earth’s Sunlight on Equinoxes and Solstices from Space
A solstice is an astronomical event that happens twice each year
when the Sun's apparent position in the sky, as viewed from Earth,
reaches its northernmost or southernmost extremes. The name is
derived from the Latin sol (sun) and sistere (to stand still),
because at the solstices, the Sun stands still in declination; that
is, the apparent movement of the Sun's path north or south comes to
a stop before reversing direction.
The term solstice can also be used in a broader sense, as the date
(day) when this occurs. The solstices, together with the equinoxes,
are connected with the seasons. In some cultures they are considered
to start or separate the seasons, while in others they fall nearer
The Sidereal Year – Measured against distant Stars
Analemma for Earth plotted as seen at noon
from the Royal Observatory, Greenwich
What a year on Earth really looks
like ( 9:28 mins)
In astronomy, an analemma ( /ˌænəˈlɛmə/; from Greek ἀνάλημμα
"pedestal of a sundial") is a curve representing the angular offset
of a celestial body (usually the Sun) from its mean position on the
celestial sphere as viewed from another celestial body relative to
the viewing body's celestial equator. The term is commonly applied
nowadays to the figure traced in the sky when the position of the
Sun is plotted at the same time each day over a calendar year from a
particular location on Earth.
Observing the Sky – Basics
14 Fun Facts About Earth: A 15-Minute Book
How old is Earth? How fast does Earth spin? What is
happening to Mount Everest, the highest place on Earth? What is the
lowest place on Earth? Learn the answer to these questions and many
more fun facts in this 15-Minute Book. Earth is the only planet in
the universe that has life. It orbits an ordinary star in the outer
edge of The Milky Way Galaxy. It is a small rocky planet, third in
line from its sun. Seventy percent of it is covered by water. It is
our home. But how much do you really know about it?
LearningIsland.com believes in the value of children practicing
reading for 15 minutes every day. Our 15-Minute Books give children
lots of fun, exciting choices to read, from classic stories, to
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