In  the context of the fourth annual polar year, the explorer Jean Louis Etienne, with the participation of large numbers of partners and sponsors,  pilots the Total Pole Airship expedition.

The primary objectives of this expedition are  to measure the thickness of the polar ice floe (sea ice) in order to measure the effects of global warming, and to establish a point of reference for future studies. In addition, an attempt is to be made  to measure the  precise positions of the North Magnetic Pole,  and the magnetic field of the Arctic Ocean.

These measurements were supposed to take place during April and May 2008, when the thickness of the sea ice is at its greatest, but the dirigible was destroyed in January, 2008.

We all know that it is the Earth that moves around the Sun. But for us, on Earth, it is the Sun that seems to move around the Earth, from East to West. This is what is called the apparent path of the Sun. It varies from season to season. It varies even more when the place of observation is at high latitude.

Remark:

• This animation illustrates the apparent path of the Sun for an observer in the Northern Hemisphere, between 40° and 50° of latitude. Someone living in the Southern Hemisphere sees the Sun toward the North, but still moving from East to West.
• Hours are expressed in Solar Time: noon (12:00) is the moment at which the Sun attains its maximum elevation.

The Greenhouse Effect is a natural phenomenon caused by the presence of certain molecules in the Earth's atmosphere (water vapor, Carbon Dioxide, Ozone, Methane...)

The Earth's surface is heated solely by solar energy (geothermal sources are 10,000 times less important).  Half of this solar energy is captured by the Earth, while the rest is absorbed by the atmosphere and, to a small extent, reflected back into space. The Earth, thus heated, itself emits radiation, but in the infrarouge.   The greenhouse gases in the atmosphere absorb  primarily these infrared wavelengths, and re-emit 80% of this energy back toward the Earth. It is this energy trap that we call the Greenhouse Effect.  It is responsible for permitting water in the liquid  state to exist on our planet, and so it favored the development of Life on Earth:  without the Greenhouse Effect, ground temperature would be around -18°C.

But human activities are beginning to disturb this equilibrium by increasing the atmospheric concentrations of several greenhouse gases, most notably Carbon Dioxide (CO₂ ) and Methane (CH₄).

An atmosphere is a layer of gas that surrounds a planet.

The Earth's atmosphere is divided by scientists into  5  theoretical layers:

• The Troposphere contains   80% of the 5 trillion tons of air!  In direct contact with and heated by the ground, this layer of air is where the important thermal exchanges responsible for meteorological  phenomena take place.
• In the Stratosphere, the temperature gets higher as altitude increases.  This temperature inversion acts as a limit for clouds. It is here that we fiind the Ozone Layer that filters out a large part of the ultraviolet radiation coming from the Sun.
• In the Mesosphere, the temperature once again begins to drop.
• Those rare particles still present in the Thermosphere interact with solar radiation.  In absorbing this energy, they increase in temperature and ionize. This is the ionosphere. This part of the Thermosphere has important electromagnetic properties.  The International Space Station (ISS) is in orbit in the thermosphere, beyond the ionosphere.
• Partcles are so rare in the Exosphere that the probability of collisions among them is negligible. Some even escape the gravitational attraction of the Earth. Although the boundary is not clearly defined, the exosphere marks the beinning of outer space.  The majority of satellites are   orbiting in the exosphere, at altitudes between 800 km and 36,000 km.

Will a child know how to find strategies for reducing  his or her CO₂  emissions,  and so aid in the fight against Global Warming caused by the Greenhouse Effect?

This little quiz provides the teacher with a pedagogical tool for sensitizing children to their own lifestyle and its consequences at the planetary scale.

The seasons change according to the amount of sunlight reaching the surface of the Earth. The Earth’s axis is tilted  as it revolves around the sun. Summer occurs when a hemisphere is tilted towards the sun.  The Tropics of Cancer and Capricorn mark the regions of the Earth where the Sun reaches the zenith at least once a year.
Note: This animation takes a geocentric view of the Earth, and so the axis oscillates during the course of the year. Were a heliocentric view chosen, the Earth’s axis would have a fixed inclination throughout the year.

The seasons are three-month periods separating the equinoxes (spring, autumn) and the solstices (summer, winter).

The changing seasons are linked to the variation of the Earth's axial tilt comparative to the plane of the ecliptic.
The Earth’s rotation axis is tilted at an angle of 23.5° from the perpendicular in its year-long orbit around the sun. As the tilt is fixed in space, each of the Earth’s poles is alternately exposed more to the sun every six months.

Diagrams are not drawn to scale.

The Earth is tilted on its orbit. This causes an unequal amount of sunshine to fall in different parts of the planet during the course of a year, and this is responsible for the seasons. You can use this animation  to illustrate the  variations in the length of daylight,  and the seasons,  in the different hemispheres.
The three cities represented  (Stockholm, Brazzaville and Cape town) are located on the same meridian.
The animation is not drawn to scale.