| The most energy efficient method of getting there is to launch oneself into an orbit whose aphelion reaches the orbit of Mars and whose perihelion is the orbit of the Earth. |
| In the orbit of a planet, means the line joining its aphelion and perihelion. |
| The date of passage of the Earth in perihelion and that of passage in aphelion advance in our calendar. |
| But it's not that simple either, because the dates of the perihelion and aphelion are also shifting. |
| Furthermore, any resonance with the Earth is illusory in that Mercury is not well placed for observations except during its brief greatest elongations near its aphelion. |
| At present the earth is about three millions of miles nearer the sun in perihelion than in aphelion. |
