12-Sep-2020: These are the Facts about Perihelion, Aphelion & Astronomical Unit:
The Earth revolves around the sun in an elliptical path, being at one of the foci or focal points. In early January, Earth reaches its closest position to the sun.
Astronomers call this point perihelion, and at this time Earth is about 91.4
million miles (147.1 million km) away from the sun, according to NASA.
Keep in mind that Earth's distance from the sun does not determine the
seasons we experience; the seasons are determined by the tilt of the planet's
axis. This is why the season occurring in Earth's Southern Hemisphere is always
in opposition to the season in the Northern Hemisphere.
Half a year after perihelion, Earth reaches its farthest distance from
the sun, which is called aphelion. At that moment, the planet is approximately
94.5 million miles (152.1 million km) from the sun. Aphelion occurs in early
July.
Perihelion and aphelion average out to about 93 million miles (150
million km).
The International Astronomical Union (IAU) is responsible for maintaining
and approving a special set of units in astronomy, formally defined in
1976.
One of the most important of these is the astronomical unit. It is a unit
of length approximating the Sun-Earth distance (of about 150 million
kilometres) which is of convenient use in astronomy. According to its
definition adopted by the XXVIIIth General Assembly of the IAU (IAU 2012
Resolution B2), the astronomical unit is a conventional unit of length equal to
149 597 870 700 m exactly. This definition is valid irrespective of the used
time scale.
The unique symbol for the astronomical unit is au. The IAU also defines
other astronomical units: the astronomical unit of time is 1 day (d) of 86,400
SI seconds (s) (SI is the International System of Units) and the astronomical
unit of mass is equal to the mass of the Sun, 1.9891×10^30 kg.
