Perihelion and aphelion

The perihelion (/ˌpɛrɪˈhiːliən/) of any orbit of a celestial body about the Sun is the point where the body comes nearest to the Sun. It is the opposite of aphelion (/æpˈhiːliən/), which is the point in the orbit where the celestial body is farthest from the Sun.
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Application to Earth

Main article: Apsis § Perihelion and aphelion of the Earth

Earth is about 147.1 million kilometers (91.4 million miles) from the Sun at perihelion around January 3, in contrast to about 152.1 million kilometers (94.5 million miles) at aphelion around July 4 — a difference of about 5.0 million kilometers (3.1 million miles). (These dates change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles. For a table of these dates for various years, see Apsis.)

Because of the increased distance at aphelion, only 93.55% of the solar radiation from the Sun falls on a given area of land as does at perihelion. However, this fluctuation does not account for the seasons, as it is summer in the northern hemisphere when it is winter in the southern hemisphere and vice versa. Instead, seasons result from the tilt of Earth's axis, which is 23.4 degrees away from perpendicular to the plane of Earth's orbit around the sun. Winter falls on the hemisphere where sunlight strikes least directly, and summer falls where sunlight strikes most directly, regardless of the Earth's distance from the Sun.

In the northern hemisphere, summer occurs at the same time as aphelion. Despite this, there are larger land masses in the northern hemisphere, which are easier to heat than the seas. Consequently, summers are 2.3 °C (4 °F) warmer in the northern hemisphere than in the southern hemisphere under similar conditions.

Perihelion and aphelion of the Earth
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Currently, the Earth reaches perihelion in early January, approximately 14 days after the December Solstice. At perihelion, the Earth's center is about 0.98329 astronomical units (AU) or 147,098,070 km (91,402,500 mi) from the Sun's center.

The Earth reaches aphelion currently in early July, approximately 14 days after the June Solstice. The aphelion distance between the Earth's and Sun's centers is currently about 1.01671 AU or 152,097,700 km (94,509,100 mi).

Apsides and Seasons
U.S. Naval Observatory
Astronomical Applications Department

2018
Eastern Time

Phenomenon Date Time
Perihelion 2018 Jan 03 00:35
Equinox 2018 Mar 20 12:15
Solstice 2018 Jun 21 06:07
Aphelion 2018 Jul 06 12:47 {just after noon}
Equinox 2018 Sep 22 21:54
Solstice 2018 Dec 21 17:23