Dear friends of Science Maths Astronomy and Geometry.Earth does go around the
Sun, but not in a circle. Earth's orbit is an ellipse, a lopsided curve with one
end closer to the Sun than the other. On July 4, 2008, our planet is at the
distant end--a point astronomers call 'aphelion.' This puts us farther from the
Sun than we are at any other time of year. Though we feel war in JUNE/JuLY (near
aphelion time 4July), Its very good that Earths APHELION comes in JULY so we are
farthest from the SUN. we feel less heat than that if we were close to the SUN.
But that will not remain the same for ever. As Earths exis tilt angle is also
changing and Earths axis also changes move to other direction in circle in about
25000 years. so when after after the 12500 yeras time the Earths Axis will be be
in opposit direction of the tilt, than thats is today. SO that will be winter in
northern hemeisphere in JULY time when EARTH's APHELION and much cooler winters
(SEASONS WILL CHANGE WINTERS IN JUNE/JULY after 12500 years). BUT summer will be
falling with the PERIHELION TIME in JANUARY (SEASONS WILL CHANGE SUMMER IN
DEC/JANUARY after 12500 years) time and VERY HARSH summer in NORTHERN HEMISPHERE
with PERIHELION TIME
'All planets in our solar system travel around the Sun in elliptical orbits.
It's Kepler's 1st Law,' explains University of Florida astronomy professor
George Lebo. 'The eccentricity of Earth's orbit is 1.7%. In January when we're
closest to the Sun (perihelion), the distance is 147.5 million km. In July we're
152.6 million km away--a five million kilometer difference.'A distant sun means
less sunlight for our planet. 'Averaged over the globe, sunlight falling on
Earth at aphelion is about 7% less intense than it is at perihelion,' says Roy
Spencer of NASA's Global Hydrology and Climate Center (GHCC). All this explains
why July is our planet's warmest month: Northern continents baked by the
aphelion Sun elevate the average temperature of the entire globe. January, on
the other hand, is the coolest month because that's when our planet presents its
water-dominated hemisphere to the Sun. 'We're closer to the Sun in January,'
says Spencer, 'but the extra sunlight gets spread throughout the oceans.'
Southern summer in January (perihelion) is therefore cooler than northern summer
in July (aphelion).Right: Earth's orbit is eccentric but not nearly so much as
the orbits of Mars or Mercury. In this diagram solid lines trace each planet's
elliptical path around the Sun. The dotted lines show circular orbits with the
same mean radius. For more information, please visit Bridgewater College's
Interactive Planetary Orbits web site.'Another notable difference between
summers in the two hemispheres is their duration,' adds Lebo. According to
Kepler's 2nd Law, planets move more slowly at aphelion than they do at
perihelion. As a result, Northern summer on Earth is 2 to 3 days longer than
southern summer -- which gives the Sun even more time to bake the northern
continents.
Earth's land-masses are concentrated more north of the equator than south
Formula



A diagram of Keplerian orbital elements. F Periaps, H Apoapsis and the red line
between them is the line of apsides These formulae characterize the periapsis
and apoapsis of an orbit:

Periapsis: maximum speed at minimum (periapsis) distance
Apoapsis: minimum speed at maximum (apoapsis) distance while, in accordance with
Kepler's laws of planetary motion (conservation of angular momentum) and the
conservation of energy, these quantities are constant for a given orbit:

specific relative angular momentum
specific orbital energy where:

is the semi-major axis
is the standard gravitational parameter
is the eccentricity, defined as Note that for conversion from heights above the
surface to distances between an orbit and its primary, the radius of the central
body has to be added, and conversely.The arithmetic mean of the two limiting
distances is the length of the semi-major axis . The geometric mean of the two
distances is the length of the semi-minor axis .The geometric mean of the two
limiting speeds is , the speed corresponding to a kinetic energy which, at any
position of the orbit, added to the existing kinetic energy, would allow the
orbiting body to escape (the square root of the product of the two speeds is the
local escape velocity).
Earth's perihelion and aphelionThe Earth is closest to the Sun in early January
and farthest in early July. The relation between perihelion, aphelion and the
Earth's seasons changes over a 21,000 year cycle. This anomalistic precession
contributes to periodic climate change (see Milankovitch cycles).The day and
hour of these events for the next few years are:[3]




Year
Perihelion
Aphelion

2007
January 3 20Z
July 7 00Z

2008
January 3 00Z
July 4 08Z

2009
January 4 15Z
July 4 02Z

2010
January 3 00Z
July 6 11Z

2011
January 3 19Z
July 4 15Z

2012
January 5 00Z
July 5 03Z

2013
January 2 05Z
July 5 15Z

2014
January 4 12Z
July 4 00Z

2015
January 4 07Z
July 6 19Z

2016
January 2 23Z
July 4 16Z

Forwarded By Dr.BHUDIA-Science Group Of INDIA
scienceclubofindia@...
President:' Kutch Science Foundation'.Founder :' Kutch Amateurs Astronomers Club
- Bhuj - Kutch '.Life Member:'kutch Itihaas
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