Peter Gross, age 13, of Wichita, Kan., for his question:

WHY IS THE PLANET VENUS SO BRIGHT

The tiny pinpoints of light that dot our nighttime sky are distant starry suns. Like gleaming jewels, they send their light to us from millions of miles away. Some of the earth's sister planets and the moon also shine brightly at night. Their light, however, is not their own. It is light reflected from our closest star  the sun.

One of the most conspicuous objects of the evening or morning sky is the planet Venus. Sometimes it is brighter than the brightest star, and sometimes it dwindles to a dim speck and disappears. The reason for this, of course, is that Venus has the inside track in its orbit around the sun, and travels its circuit in less time than the earth does. It shines brightest in our sky just before and just after it passes us.

Because of its orbit, Venus is not seen during most of the night. We see it brightly shining in the evening, as it moves toward the earth and is still east of the sun. When Venus is on the same side of the sun as the earth, it is a scant 25 million miles away. However, its sunlit side is facing the sun, and we view it as a thin, fuzzy halo. As Venus begins to move away from the earth, toward the western leg of its orbit, we can see it in the early morning hours.

Although Venus is sometimes called the morning or evening star, we know it is not a star at all. Stars are heavenly bodies, like our sun, that are seething, fiery furnaces. Venus is a planet, like Mars and Jupiter, and can be seen only because it reflects light from the sun. It shines so brightly because it is our nearest planetary neighbor and also because it reflects about three fourths of the sunlight it receives.

Venus has always been somewhat of a mysterious planet. Early in the 17th century when the first telescopes were trained on it, there were high hopes for startling discoveries. After all, only the sun and the moon were brighter, and it was the closest planet to the earth. Astronomers had visions of a planet similar to the earth with seas, continents and other earthlike features. Sad to say, the scientists were disappointed. All they could see was a mass of yellowish clouds. The planet lacked the spectacular rings of Saturn or the icecaps of Mars, and didn't even have any moons.

Since those first glimpses, Venus has remained a mystery. For although telescopes have been greatly improved, no one has yet seen the surface of the planet. Even in 1974 when Mariner X flew past Venus on its way to Mercury, dense clouds prevented so much as a peek at the Venusian surface.

From now until April, 1977, Venus will be seen in the western portion of the evening sky, after sunset. After that it will be seen as our morning star in the eastern portion of the sky just before sunrise.