Fascinating Planets​—for Our Enjoyment

“HELLO. I’m glad you called me over this evening. I’ve been looking forward to seeing some of the planets through your telescope.”a

“And I’m glad you could come. It’s a beautiful clear evening.”

“Is that your telescope? It looks so small. I was expecting to see a long tube, balanced on a tall tripod.”

“Yes, this is known as a catadioptric telescope. Though this instrument is only nine inches long, the optical path is folded back and forth inside the tube so that it has a focal length of more than four feet.”

“So that’s the way it works. . . . Is it dark enough to begin yet?”

The Phases of Venus

“Yes, this is the best time to see Venus, before the sky is really dark. Do you see that bright star over there in the west?”

“Say, that really is bright.”

“Yes, next to the sun and the moon, Venus is the brightest object in the sky. You can see it even in broad daylight if you know where to look. There, I have it in view. Would you like to sit down and look?”

“So this is Venus. Why, it looks like the moon when it is not quite half full. Why is that?”

“Venus goes around the sun in an orbit inside the earth’s orbit. So it is often between us and the sun. Of course, only half of Venus is lighted by the sun, and right now we can see less than half of its daylight side. So what we see is a crescent.”

“Then as Venus moves in its orbit, does its appearance change shape as the moon does when going through its phases?”

“Correct. In its present position, Venus is moving closer to the line between the earth and the sun. If we look at it, say, a month from now, the crescent of light will be thinner. But, at the same time, it is coming closer to the earth, so it will appear larger in the telescope. Just before it crosses in front of the sun, it will look perhaps twice as large as it does now, but only the thinnest crescent will be visible.”

“Well, that certainly is interesting. What is it like on Venus?”

“Venus is very nearly the same size as the earth. But no one has ever seen its surface, for it is always covered with dense clouds. However, men have sent space probes to Venus with instruments that returned signals as they parachuted to the surface. It is very hot there, over 900 degrees Fahrenheit. So there can’t be any rivers or lakes or oceans on Venus. Its atmosphere is almost a hundred times as dense as ours, and it is composed mostly of carbon dioxide.”

“That doesn’t sound like a very pleasant climate.”

“No, you wouldn’t want to spend a vacation there. Years ago, some scientists thought there might be life on Venus, but we know now that that is impossible.”

Elusive Mercury

“It’s getting quite dark now. What are we going to view next? Can we see Mercury?”

“Not tonight. Mercury is even closer to the sun than Venus. So it is almost never far enough away from the sun in the sky to be above the horizon after dark. Only once or twice a year, on the average, is it easy to get a glimpse of it. But there are two special occasions when Mercury can be seen clearly. One is when a total eclipse of the sun blots out its light for a few minutes. The other is when Mercury crosses the sun’s disk. But that is not due to happen again until the year 2003.”

“That’s a long time to wait. Is there anything else that we can see tonight?”

Jupiter and Its Moons

“Let’s turn the telescope to the planets outside the earth’s orbit, first to Jupiter. Jupiter is the largest planet in the solar system, and even though it is almost half a billion miles from us, it is very prominent in the sky.”

“How big is Jupiter?”

“Its diameter is about 87,000 miles, some eleven times as great as the earth’s, and just about one tenth the diameter of the sun. There, I have it in view. Look and tell me what you see.”

“It is a large, bright disk, like a full moon. And there are several bright stars beside it.”

“Those are some of Jupiter’s moons. Four of them are bright enough to be seen with a small telescope. Jupiter has a big family of much smaller moons. The thirteenth was discovered just last year. But the four that you see have been known ever since Galileo first turned his telescope on Jupiter, They are all sizable bodies; one is even larger than Mercury.”

“I notice that they are in a nearly straight line. One is on the left side and three are on the right.”

“If you look again tomorrow night, you will see them all in different positions. They are located at different distances from Jupiter, and, therefore, circle the planet at different speeds. Because we see the orbits on edge, they always stay pretty much in a line. As for Jupiter itself, let me change the magnification from 80 to 160 power. You said it looks like the full moon, but do you notice any difference now?”

“Yes, it doesn’t look blotchy like the moon. But I can see some fine lines running across it, or should I say bands of darker color, in line with the moons. What causes these?”

“They are probably bands of clouds, driven around Jupiter by prevailing winds, like the trade winds we have on earth. Jupiter’s atmosphere is evidently very thick and dense. Astronomers have identified methane and ammonia gases, as well as hydrogen, in it. The clouds may be crystals of solid ammonia. Since the average density of Jupiter is only one fourth that of the earth, the bulk of the planet must consist of gases. . . . Do you notice anything else on the surface?”

“Do you mean a spot? Down in the lower hemisphere?”

“Yes. That is the famous ‘Great Red Spot’ of Jupiter.”

“What is that spot​—smoke or something?”

“There have been a lot of theories, including one that supposes that there is a volcano under the clouds. But that is not likely, since, at times, the spot shifts considerably, east and west. It does not seem to be anchored to anything solid underneath. Probably the ‘Great Red Spot’ is a giant storm in Jupiter’s atmosphere. It was first noticed nearly a hundred years ago. It changes quite a bit in size, shape and color, but it stays there. If the spot is really a storm, it is immense, big enough to engulf the whole earth.”

“I can see why you find Jupiter so interesting. . . . What is that reddish star over in the southeast? Could it be Mars?”

Mars’ Forbidding Climate

“You are right. Mars is our best-known neighbor in space. Although Venus comes closer, Mars has gotten the lion’s share of study and publicity. The reason is that when Mars is closest to us, it is fully lighted by the sun and is easy to observe and study. I should warn you, though, when you look at Mars, it may disappoint you, for it is not as spectacular in a small telescope as the larger planets. Still, there’s one feature visible now that is well worth seeing. There, look.”

“It does look small. But its red color surely stands out. And there is a distinct white spot on one side. Is that the ice cap?”

“Yes. In its present position, Mars’ south pole is tipped toward us, and that is where you see the polar ice cap. Mars, though much smaller than the earth​—its diameter is only about 4,000 miles—​is similar in some respects. For one thing, its axis is tipped about 24 degrees from the plane of its orbit, almost the same as the earth. Therefore, Mars goes through seasons as it travels around the sun, just as the earth does. Another similarity is that Mars rotates on its axis in just over twenty-four hours.”

“Is that why some people think there might be life on Mars?”

“Perhaps so, but in other ways Mars is very different from the earth. It has an atmosphere less than one percent as dense as ours, and that is mostly carbon dioxide. There is little or no water on Mars, so the ice cap you see is not ordinary ice, but is solid carbon dioxide, what we call dry ice. It is now summer in Mars’ southern hemisphere, and the ice cap is shrinking. Under twenty-four hours of sunshine a day, it will be all gone in a few weeks.”

“It must be really cold there to form dry ice. But isn’t it warmer in the temperate zones of Mars?”

“Yes, the highest temperature reported by space probes for Mars’ equator was about 60 degrees Fahrenheit, but overnight it plunges to 100 degrees below zero, even in midsummer.”

“What a forbidding climate! The planets are truly fascinating. What are we going to see next?”

Eros, a Little Island in Space

“There are so many fascinating things in our solar system. Do you see those two bright stars, one above the other? Those are the Twins, Castor and Pollux. Diagonally down to the right of the lower one is another star, not so bright. Astronomers call it Kappa Geminorum. Through the telescope last night, I saw it with two other fainter stars, one to the left and the other below it, forming a right triangle with Kappa at the right angle. Now look at it and tell me what you see.”

“I see the bright star and the other two where you say, but there is a fourth star, on the line between the two dimmer ones.”

“Right. That wasn’t there last night, so it must be a planet. Remember that a fundamental difference between a star and a planet is that a star stays in a fixed position in the sky, year after year, but a planet moves.”

“What planet is it?”

“It is one of the minor planets, or asteroids, called Eros. It is quite exceptional in that it comes close to the earth, and moves rapidly in the sky. As you say, right now it appears on a straight line between the two stars. But it is moving so fast that an hour from now it will be quite out of line with the others.”

“It doesn’t show a disk, like the other planets. If it weren’t moving, you couldn’t tell it from a star.”

“It is very small, and it isn’t even round. Eros is estimated to be 22 miles long and 10 miles wide. Consequently, as it rotates on its axis, once in five hours, it goes through a regular bright-and-dim cycle every two and a half hours. Eros is really just an island in space, about the size of one of the Caribbean islands.”

“Does Eros come close very often?”

“No, it is really a rare thing to be able to see such a tiny planet. If Eros were confined to the region out between Mars and Jupiter, where most of the asteroids are, we would never see it. But it is on an orbit that brings it, at perihelion, that is, at the point nearest the sun, quite close to Earth’s orbit. This month, it happens, we are here to meet it, only 14 million miles away. But it will be eighty-one years before it comes as close again.”

“I can see that an astronomer has to be very patient. But how time has flown this evening! Do we have time to look at anything else?”

Saturn’s Marvelous Rings

“There’s one thing more, which I have saved till the last. Let me show you what I feel is the most beautiful sight in the heavens. It is Saturn. I’ll focus on it at 80 power. There it is, with its rings spread out for you to admire.”

“Oh! What an amazing sight! That is truly impressive. But I can see only one ring. Did you say rings?”

“Yes. Let’s double the magnification. There, look again, and see if you can see an inner and an outer ring, with a narrow black space between them.”

“Yes, now I see the two rings. The inner one is the brighter. They must be of tremendous size.”

“They are, indeed larger than anything else in the sun’s family of planets. Although Saturn itself is a little smaller than Jupiter, its rings reach out to a diameter of 170,000 miles. And in a larger telescope, one can see a third ring, much fainter, inside the ones we see here.”

“What a magnificent spectacle!”

“Saturn’s rings are unique in all the visible universe. As the planet revolves around the sun every thirty years, the angle at which we see the rings goes through phases. For fifteen years, we see them from the south, as now, and then, for a like period, from the north. And twice in a revolution, we look at them right on edge. When that happens, a person would not suspect their existence. The rings are exceedingly thin, not more than ten miles thick. And they are perfectly circular and absolutely flat and uniform, as seen in even the largest telescopes.”

“What are the rings composed of?”

“They can’t be anything solid, for if they were, the outer edge would be moving more rapidly than the inner. The fact is, however, that the inner parts of the rings are moving faster. That is just what would be expected of satellites at corresponding distances from Saturn. Therefore, Saturn’s rings must consist of billions or trillions of small particles, each revolving in its own orbit around Saturn. Judging from the mass and reflecting power of the rings, the particles must be tiny, perhaps as fine as dust.”

“But how did so many billions of particles get out there in such an amazing formation? How do they remain in stable orbits, without suffering collisions that would disrupt the rings?”

“No one has the least idea. It seems to me that this is another example of what we see so often in Earth’s plant and animal creation. It is as if the Creator, Jehovah, took delight in demonstrating not only his tremendous power and intelligence, but also his infinitely diversified imagination in designing both animate and inanimate creation in such overwhelming variety. Think of God’s loving consideration in putting man on the earth, a planet with such a clear atmosphere, and granting him the intelligence and curiosity to invent telescopes and to turn them heavenward.”

“Do you mean that Saturn’s rings and all these other wonderful things that I have been viewing tonight were put there just for men to study and enjoy?”

“Only God knows why he made all these things. But from man’s standpoint, could there have been a better reason? Does not what you have seen of the physical universe make you stand in awe of its grand Creator? Are we not moved with appreciation for his love toward us in providing such things to enjoy, along with other blessings of life?”

“By all means. But what I have learned this evening leaves me with a couple of questions. Have not many generations of astronomers only scratched the surface of what there is to learn about the universe? And since many of the phenomena that you have spoken about happen so rarely, maybe only once or twice in a lifetime, does it not make you feel shortchanged, so to speak, that you cannot live long enough to see all the wonders of creation?”

“That is just one more reason why it does not make sense that God made man to live only a few score years. Why, in a thousand lifetimes we would not run out of things to enjoy watching and learning about in the marvelous heavens of Jehovah’s handiwork. How reasonable, then, is the Bible’s viewpoint that God put man on the earth to live forever.”​—Rev. 21:4.

“Surely you have given me much to think about. Thank you for an unforgettable evening.”

[Footnotes]