Perihelion, Aphelion and the Solstices
Changing Elliptical Orbit
Earth orbits the Sun in an elliptical path, which means that there is 1 point of the path when the Sun is at its closest to the Earth and 1 point when it is furthest away.
Orbit Changes Shape
The shape of this path varies due to gravitational influences of other planetary objects, particularly the Moon.
Approximately every 100,000 years, Earth's orbital path changes from being nearly circular to elliptical. The difference of the Earth’s orbital shape from a perfect circle is known as its eccentricity. An eccentricity value of 0 is a circular orbit, while values between 0 and 1 describe an elliptical orbit.
Perihelion in Washington DC, District of Columbia, USA was on
Wednesday, January 4, 2017 at 9:17 am EST (Change city)
Distance from the Sun's center to Earth's center was 147,100,998 km (91,404,322 mi)
|2017||January 4, 2017 9:17 am||91,404,322 mi||July 3, 2017 4:11 pm||94,505,901 mi|
|2018||January 3, 2018 12:34 am||91,401,983 mi||July 6, 2018 12:46 pm||94,507,803 mi|
|2019||January 3, 2019 12:19 am||91,403,554 mi||July 4, 2019 6:10 pm||94,513,221 mi|
|2020||January 5, 2020 2:47 am||91,398,199 mi||July 4, 2020 7:34 am||94,507,635 mi|
|2021||January 2, 2021 8:50 am||91,399,454 mi||July 5, 2021 6:27 pm||94,510,886 mi|
|* All aphelion/perihelion times are in local Washington DC time.|
Earth's Perihelion and Aphelion
The Earth is closest to the Sun, or at the perihelion, about 2 weeks after the December Solstice, when it is winter in the Northern Hemisphere. Conversely, the Earth is farthest away from the Sun, at the aphelion point, 2 weeks after the June Solstice, when the Northern Hemisphere is enjoying warm summer months.
Is the Timing a Coincidence?
The dates when Earth reaches the extreme points on its orbit are not fixed because of the variations in its eccentricity. In 1246, the December Solstice was on the same day as the Earth reached its Perihelion. Since then, the Perihelion and Aphelion dates have drifted by a day every 58 years. In the short-term, the dates can vary up to 2 days from one year to another.
Mathematicians and astronomers estimate that in the year 6430, over 4000 years from now, the timing of the Perihelion and the March Equinox will coincide.
Perigee and Apogee
Like the Earth's orbit around the Sun, the Moon's path around the Earth is elliptical. The point in the Moon's orbit that is closest to the Earth is called the Perigee and the point farthest from the Earth is known as the Apogee. The terms are also sometimes used interchangeably with the Earth's Perihelion and Aphelion.
Did You Know...
...that the words Perihelion and Aphelion come from ancient Greek, where peri means close, apo means far, and helios means the Sun? They are used in astronomy to refer to the closest and farthest points of the orbits of any object revolving around the Sun. Together, they are called apsides - the points of least or greatest distance of a celestial object in orbit around another astronomical body.
The Science of Seasons
- What Causes Seasons?
- Earth's Axis Is Tilted
- Meteorological vs. Astronomical Seasons
- What Is a Solar Analemma?