Image via NASA.
The fact is that Earth's orbit is almost, but not entirely, circular. So our distance from the sun doesn't change much. Today, we are about 3 million miles (5 million km) further from the sun than we will be in six months. That contrasts with our average distance from the sun of about 93 million miles (150 million km).
The word aphelion, by the way, comes from the Greek words apo sense away away outside and helios, for the Greek god of the sun. Apart from the sun. We are today.
Looking for the exact distance from Earth to the sun in aphelion? They are 94,507,635 miles (152,095,295 km). Last year, on July 4, 2019, the Earth in aphelion was slightly further away, at 94,513,221 miles (152,104,285 km).
The aphelion sun seems smaller in our sky, as shown in this composite image. This image consists of 2 photos, taken a few days from a perihelion (the closest point on Earth to the sun) in January 2016, and an aphelion (the farthest point from Earth from the sun) in July 2017. The gray border around the sun (actually the perihelion photo) illustrates that as seen in our sky the sun is approximately 3.6% larger in perihelion than in aphelion. This difference is, of course, too small to detect with the naked eye. Peter Lowenstein in Mutare, Zimbabwe, who captured the photos and created the composite material, wrote: "Although 18 months and a few days apart from the events due to adverse weather conditions, they show that there is an unmistakable difference in the size of the sun seen from the Earth when closest in perihelion and farthest in aphelion. "
This animation shows what's also in the image above ... the size difference of the sun between Earth's perihelion (closest point) and aphelion (farthest point).
This is what causes the seasons. The seasons are not due to the changing distance from Earth from the sun. We are always farther from the sun in early July during northern summer and closer in January during northern winter.
Instead, the seasons are the result of the Earth's tilt on its axis. Right now, it is summer in the northern hemisphere because the northern part of the Earth is more inclined towards the sun.
Meanwhile, it is winter in the southern hemisphere because the southern part of Earth is steeper from the sun.
The variable distance from Earth to the sun does affect length of seasons That's because, at our furthest point from the sun, like now, Earth is traveling the most slowly in its orbit that makes summer the longest season in the northern hemisphere and winter the longest season in the southern half of the globe.
By contrast, winter is the shortest season in the northern hemisphere, and summer is the shortest in the southern hemisphere, in each case in nearly five days.
Land in perihelion and aphelion 2001 to 2100
Bottom line: Planet Earth reaches its most distant point from the Sun by 2020 on July 4. Astronomers call this annual point on Earth's orbit our aphelion.
EarthSky Astronomy Kits are perfect for beginners. Order yours today.
Why isn't the hottest weather on the longest day of the year?
