Suzanne Marie, age 11, of Saugus, Massachusetts, for her question: 

Why isn't Venus brightest when closest to the earth?

There are times when Venus outshines every star in the dark, velvety sky. There are times when the golden planet comes within 26 million miles of us, closer than any other planet. You would expect it to shine its brightest during its closest approaches. Not at all. At its closest point to earth,Venus becomes invisible. When our sister planet is closest to the earth, it is passing between us and the sun. The side opposite from us is facing the sun and bathed in radiant daylight. The side facing us is shrouded in the dark shadows of night, and Venus is invisible from the earth. There are times when we see the full daylit surface of Venus, but at these times the golden planet is on the far side of its orbit. The sun is between us, shining full on the side that is facing the earth.

We are 26 million miles farther from the sun than Venus. Both planets travel around yearly orbits, but Venus occupies the smaller, inside traffic lane. It completes each orbital trip in 225 earth days, while our yearly orbit takes 365 1/4 days. As both planets circle the sun, Venus on the inside traffic lane is forever catching up to us and passing us. Seen from the earth, the golden planet swings in a loop first east and then west of the sun.

Between loops it swings from behind the sun to a position between us and the sun. This weaving hoedown is completed and repeated every 584 days. From our outer traffic lane, we observe the daylight creep from rim to rim across the disk of the golden planet. Through a small telescope, you can watch Venus pass through phases like the moon. At the full phase, Venus is on the far side of the sun and we are separated by a distance of 160 million miles.

The distance appears to rob the golden orb of its size and brilliance. From its full phase, Venus swings eastward from the sun, rising later each night in the role of the Evening Star. ,It is coming closer now, catching up to the earth in our outer traffic lane. But at the same time, its full phase is dwindling to the half and quarter phase. As it approaches, the disk of the planet appears to prow bigger, until it seems six times larger than the full phase. And because of its nearness, the thin quarter phase is 2 1/2 times brighter than the full phase we saw when Venus was on the far side of the sun. At last it catches up and passes us on its inside lane, coming between us and the sun. For a few nights, the dark side of Venus is turned toward us and at this closest approach our sister planet is invisible. Then it pulls ahead and reappears on the western side of the sun.

A new phase begins as a slim sliver of brilliance around the dark disk. At its quarter phase, Venus is 14 times brighter than Sirius, the brightest of the stars. As the slim sliver grows to half phase, Venus is receding from us. We see more of its sunny surface, but with distance, the size of the disk grows smaller and its brilliance grows dimmer. There are four key points in the weaving path of Venus, and astronomers have a term for each of them. At full phase, when we are on opposite sides of the sun, Venus is at superior conjunction. The next key point arrives 200 days later when Venus reaches its eastern elongation  the limit of its eastern distance from the sun. Then it swings westward for 144 days. Midway it passes between us and the sun at the point called its inferior conjunction. The limit of its loop westward is called the western elongation. From this point it loops eastward, back to superior congiunction and on to eastern elongation once again.