5. The Four Seasons
Is the changing seasons caused by the change
in the distance between the Sun and the Earth?
No. If it is, then
– The northern and southern hemisphere should have
the same season, not opposite season like we have.
– We should experience real seasonal changes in
Hawaii also.
7. Solstices and Equinoxes
• Equinox :
– An equinox is one of two opposite points on the
celestial sphere where the celestial equator and
ecliptic intersect.
• Solstice:
– A solstice is either of the two times of the year
when the sun is at its greatest distance from the
equator.
8. Earth sun relationship
• Due to the tilted position, the area receiving the
maximum intensity moves north and south, between the
tropic of Cancer (latitude 23.5°N) and the tropic of
Capricorn (latitude 23.5°S). This is the main cause of
seasonal changes.
• On 21 March and 23 September areas along the Equator
are normal to the sun’s rays and experience a zenith path
of the sun. For all areas of the earth these are the
equinox days (day and night of equal length)
9. The Reasons for the Seasons on Earth
• The seasons on Earth are caused by the 23.5º tilt of its
rotation axis, and its revolution around the Sun.
• Although the distance of the Earth to the Sun changes
slightly as it orbits around the Sun, its effect is not big
enough to cause the four seasons.
• The seasons for other planets may be due to the
changing distance to the Sun, not the tilt of their
rotation axis…For example, the orbit of Pluto has a
very large eccentricity.
10.
11. Thermal radiation
• The phenomenon of thermal radiation is described as the transport of
energy through electromagnetic waves. Unlike conduction and convection,
radiative heat transfer is not bound with material, it can even occur
through vacuum. Every body whose temperature is above absolute zero
radiates energy in the form of electromagnetic radiation. The spectral
distribution of the energy radiated from any body depends on the
temperature of its surface. The higher the temperature of the body, the
lower is the wavelength of the radiation that makes the major portion of
the total emitted radiation.
• Since the temperature of most building components and their
surroundings are much less as compared to hat of sun, the spectral
distribution of their emitted radiation as more share of larger wavelength.
It means, radiation emitted from such bodies is thermal radiation. Typical
wavelengths of radiation from building components are in the range of 3
to 800 ?m that makes the basis of radiative heat exchange between the
buildings and their surroundings.
