Earth and Moon & The Science of it












Earth Components:

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

( Aurora);  - 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 plant types.

These regions called Biomes include deserts, tundra, tropical rainforest, savannah, and alpine areas

The Ecosystem 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






Iceland Ice Cap



Ice Caps and Glaciers


Storehouses of freshwater


Ice Caps






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 oceans.

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 know it.



Ocean Temperature Variations between Solar Cycles




Ocean Temperature Maps



El Niño and La Niña  -  and the Solar Cycles


Solar 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 Niño events.




Solar Activity Controls El Niño and La Niña


El Nino/La Nina Explainer ( 8 mins)


El Niño and La Niña - Maps by Years ( 3 mins)


El Niño  & the Warm Waters of the Pacific Ocean ( 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.






Tidal Forcing by Earth-Moon-Sun System







Recession of the Moon & Earth’s Tidal Bulge

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 Salinity

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 mins)

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.) 



Aurora Borealis


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 photo)


LINK to our Auroras and Double Rainbows Page w Video








Earth’s Magnetic Field


The Magnetosphere




LINK to our PAGE: 

 Earth Magnetic Field  - Magnetic Reversal  & The Magnetosphere



The Inner and Outer  Van Allen Radiation Belt





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,[3] 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.


Implications 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"....


Earth's 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 right.





Van Allen Radiation Belts to be Explored by New Spacecraft | NASA RBSP Storm Probe Mission Video  ( 3 mins)


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 thousand mph.



Lightning  -  Cloud-to-cloud


Lightning from the Ground up


Lightning Bolt


Wind turbines are silhouetted by lightning in Jacobsdorf, in Brandenburg, Germany



Lightning & lightning storms -

one of the most unpredictable

forces of nature.



Lightning Sprites - They Occur high

on top of thunderstorm Clouds & appear

as luminous white - bluish or reddish-orange flashes.





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.[1] 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.[4] 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 called Fulminology. ...


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> xyXCUIDfHpPa8ASQ8YCwAw&ved=0CAcQ_AUoAA&biw=1680&bih=871



Eratosthenes' measurement of the

Earth's circumference




Eratosthenes 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[1] – c. 195 BC[2]) 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 


Eratosthenes also measured the tilt of the Earth axis by 23.5 degrees, which gives us the seasons .








Earth’s Rotation

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).[132] 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".




Measuring Latitude & Longitude


Prime Meridian GMT England






Longitude GMT Monument - East/West Meridians


Equator Monument - North/South




Measuring Latitude & Longitude & Greenwich Mean Time

Do you remember learning about how to measure latitude and longitude? On the Earth, latitude 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 country?




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.


Longitude & Latitude


Greenwich 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)!


Age of Ocean Floor ??











Blue Moon??






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 Moon's Orbit?

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 Earth.


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.

Synchronous Rotation

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




Earth's Moon Maps - National Geographic






Earth's moon is tilted 5 degrees from the

 plane of the solar system.



Moon Orbits Earth




Moon 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

nearby storms.




A Moon Halo with a Rainbow effect.



Moon's Halo


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.



What 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.

Animation //



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 slightly longer.

Milankovitch cycles

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 middle.



The Sidereal Year – Measured against distant Stars





Analemma for Earth plotted as seen at noon

 GMT from the Royal Observatory, Greenwich




What a year on Earth really looks like ( 9:28 mins)

Sun’s Analemma

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? 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 mysteries, to books of knowledge. Open the world of reading to a child by having them read for 15 minutes a day.



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