# Is it possible to affect Earth's orbit so that, say, aphelion happens sooner?

As part of its natural cycle, the sun is currently drifting away from the Earth, it's predicted to reach its farthest point by July 4th in 2020, at which point the distance between the Sun and Earth will start to close.

Do humans have enough power to control earth's orbit so that the sun starts its trip back sooner? I just can't wait for the heat to come back.

• I can't find it now but once I saw a calculation of attempting to stop the Earth rotating. It used a large number of shuttle engines and an implausible supply of fuel. Even so, it came nowhere close. I expect that changing the orbit would be even harder. Just consider how much momentum the Earth has. – badjohn Feb 22 at 22:54
• Look at this question of mine: astronomy.stackexchange.com/questions/32470/…. Aphelion is only coincidentally near the solstice. You need to change the Esrth's tilt which is also very hard. – badjohn Feb 22 at 23:00

Humans don't have this capacity. The Earth has a kinetic energy of about $$10^{33}$$ joules, relative to the sun. Even if we put the total energy that humans use per year into the Earth's orbit (about 10^{24} joules) we still only have one-billionth of the kinetic energy of the Earth.

Moreover, the annual changes in temperature have very little to do with the distance from the sun, they are caused by the tilt of the Earth to the sun. For people in the Northern Hemisphere, the greatest distance to the sun occurs in the middle of summer when the temperature is usually at its hottest.

While we can't change the orbit of the Earth very much, we have been much more successful (!) at changing the composition of the atmosphere. The build-up of CO2 and other greenhouse gasses is warming the Earth significantly, and we can expect significant harmful consequences from this warming. We might like "warmth" but we don't like the rising sea levels, droughts, floods, and other effects of global climate change.

This isn't exactly an answer to the question as asked, but it's close enough to one that you might find it interesting and hopefully helpful in some way.

The gravitational force of the Sun on the Earth is given by

$$F_{Grav} = \frac{GM_{Sun} M_{Earth}}{a^2}$$

where $$a$$ is the semimajor axis of Earth's orbit and is about 1.5E+11 meters and $$GM_{Sun}$$ is the standard gravitational parameter of the Sun, or about 1.327E+20 m^3/s^2. The mass of the Earth is about 5.97E+24 kg.

The force due to radiation pressure of the Sun's light on the Earth can be estimated as

$$F_{Rad} = Area_{Earth} \frac{I_{Sun}}{c} = \pi R_{Earth}^2 \frac{I_{Sun}}{c}$$

where the mean radius of the Earth $$R_{Earth}$$ is about 6.37E+06 meters and the intensity of sunlight on the Earth $$I_{Sun}$$ is roughly the solar constant ($$G_{SC}$$) and is about 1361 Watts/m^2.

The ratio of the two

$$\frac{F_{Rad}}{F_{Grav}} = \frac{\pi R_{Earth}^2 I_{Sun} a^2}{c \ GM_{Sun} M_{Earth}}$$

That ratio is about 1.6E-14, which is pretty small!

If we somehow made the surface of the Earth darker or lighter with different distributions across the planet versus time of year and time of day, we could (i.e. changing Earth's visible light albedo) we could play tricks with its orbit.

For example, if we reflected more daylight westward (prograde) than eastward (retrograde) throughout the year, we could over billions of years bring Earth's average orbit ever-so-slightly closer to the Sun. Of course changing Earth's visible light albedo would have dramatic and Earth-changing heating and cooling effects on the Earth, but that's a different story.

We could also flip that around every six months in order to circularize our orbit and keep us a more constant distance from the Sun, but as @JamesK's answer points out it's cold in one hemisphere (and warm in the other) because of the tilt of Earth's axis, not because of the change in distance from the Sun.