The Solar System: Venus

For millennia, people have enjoyed the sight of the “evening star” shining brightly in the western sky shortly after sunset. Outshining all other stars, this remarkable beacon seems to brighten to unbelievable glory as twilight fades to night. It rises higher night after night and then stops and begins to sink lower each evening until it vanishes below the horizon. Sometime later, it reappears just before sunrise in the eastern sky as the bright “morning star.”

What did the ancient astronomers think about this magnificent object and its peculiar celestial dance? They called it “Venus,” after the Roman goddess of love and beauty.1

Physical Properties

With modern technology, we have learned a great deal about Venus. It’s not a “star” at all, but a planet—a small rocky world that shines only by reflected sunlight.2 In fact, Venus is about the same size as Earth.3 So when we look at Venus, it’s fun to think that this is also how tiny Earth would appear if viewed from Venus.

The composition of Venus is also similar to Earth, and its orbit is physically closest to Earth’s of all the planets. For these reasons Venus is sometimes referred to as “Earth’s sister” or “Earth’s twin.”4 But there are far more differences than similarities.

An examination of the surface of Venus has proved quite challenging because Venus is permanently enshrouded in thick clouds of sulfuric acid and toxic sulfur dioxide, masking all surface features. The atmosphere is comprised mainly of carbon dioxide and is the thickest atmosphere of the four terrestrial planets. At the surface, Venus has a crushing air pressure that is 92 times greater than Earth’s! This thick atmosphere acts like a blanket, trapping solar energy and warming the planet to unbelievable temperatures. And since Venus orbits 26 million miles closer to the sun than Earth does, Venus already endures nearly twice the solar energy. The greenhouse effect causes the surface temperature of Venus to approach 900°F—the hottest of any planet in our solar system.

In 1990, the NASA spacecraft Magellan was inserted into orbit around Venus and began systematically mapping the surface using radar. Since radar is not blocked by clouds, Magellan was able to map the topography of Venus in unprecedented detail. The four-year-long mission revealed that Venus has many of the same geological features found on Earth, including mountains, valleys, canyons, volcanos, lava flows, craters, and plains. Venus also has two major “continents”—Ishtar Terra and Aphrodite Terra. But since there is no liquid water on Venus, these “continents” are recognized only by their high elevations.

Venus also has geological features not found on Earth, such as arachnoids, novae, tesserae, coronae, and pancake domes. Arachnoids are regions where the terrain has been folded and broken into a gossamer-looking structure resembling a spider web. Novae are “radially fractured centers” between 60 and 200 miles in diameter. Sixty-four novae have been discovered on Venus.5 Tesserae are complex ridged terrains found on plateaus. “Corona” is from the Latin meaning “crown.”6 They are oval-shape features thought to be produced by plumes of upwelling magma that cause the surface to bulge and then collapse in the center, forming a crown-like ring. Pancake domes are similar in most respects to shield volcanoes on Earth, such as Mauna Loa in Hawaii. However, pancake domes are flatter and broader than their terrestrial counterparts. Venus has no moons and virtually no magnetic field.

Such similarity, yet with differences, is consistent with the nature of God. God is the source of creativity and has created a diversity of objects within the universe, and yet there are similarities since the entire universe was created and is upheld by the same God. Differences and similarities are seen in the biological world, the world of particle physics, and in the solar system as well. But in the secular view, how can we make sense of this? Earth and Venus are nearly identical in size and bulk composition and have similar orbits. In the secular view, they have a similar history too. So why would Earth’s “sister” be so radically different from Earth? There are secular speculations for such things—but such diversity is expected in the Christian worldview.

A Day on Venus

Venus has the most circular orbit of any planet in the solar system. Its axial tilt is only three degrees, so there are no seasons on Venus. Since it orbits closer to the sun than Earth does, Venus orbits faster and completes a circuit every 7.4 months. But its day is much longer than Earth’s. Venus rotates once every eight months, so its day is actually longer than its year. This is the sidereal day—the rotation of Venus relative to the stars.7 What is even more intriguing is that Venus rotates backward. All eight planets orbit the sun counterclockwise, as viewed from the solar system’s North Pole. Most of the planets also rotate counterclockwise,8 but Venus is the exception.9 On Venus, the sun would rise in the west and set in the east—although it would be difficult to see the sun in such overcast skies.

Secularists do not have a good explanation for the backward rotation of Venus. In the secular scenario, the solar system is supposed to have formed from the collapse of a rotating nebula. The natural expectation of this would be that all planets would rotate in the same direction at about the same rate, and they would all have very little axial tilt. Venus is the worst offender to this concept, since it rotates exactly the opposite of what the evolutionary models require. But we expect such diversity in the biblical view.

The backward rotation of Venus causes its solar day to be much shorter than its sidereal day—a unique phenomenon in the solar system. Recall that the solar day is the average time from one sunrise to the next as viewed from a planet’s surface (e.g., 24 hours for Earth). This is different (and normally slightly longer) from the sidereal day because planets orbit the sun and not the stars. Since Venus rotates in the opposite direction, its solar day is reduced to 3.8 months. Strangely, this is shorter than Mercury’s solar day, even though Venus physically rotates slower than Mercury.

Phases and the Nature of the Solar System

Venus is a great target for telescope beginners. Its brightness makes it easy to find, and its size and proximity to Earth allow viewers to discern its shape through even a small, inexpensive telescope. Although the clouds on Venus prevent observations of any surface features, observers will immediately notice that Venus has phases; it is not uniformly illuminated, but appears bright on one side and dark on the other. Viewers sometime describe it as a tiny craterless “moon,” since the moon is the only other object that we readily recognize as going through phases. Just like the moon, Venus goes through new, crescent, quarter, gibbous, and full phases.10 And like the moon, these phases make it obvious to the eye that Venus is spherical, not a flat disk. But there are three differences in the phases of Venus compared to the moon.

First, the moon takes roughly one month to go through its phases, whereas Venus takes over 19 months. Since Venus orbits the sun faster than Earth does, it physically overtakes and passes the Earth every 19 months. This is called the synodic period of Venus. Since the phase of Venus as seen from Earth depends on the relative positions of Earth, Venus, and the sun, phases correlate with the synodic period.

Second, whereas the moon remains approximately the same apparent size as it goes through its phases, Venus does not. Venus appears very small when in its gibbous phase (nearly full) and appears very large when in its crescent phase.11 This is because Venus orbits the sun, not the Earth. Hence, when Venus is nearly in-between the sun and Earth and we are viewing only a thin sliver of the illuminated side, Venus is nearly as close to Earth as it gets. Conversely, when Venus is on the far side of the sun, we see it nearly fully illuminated. Galileo was the first person to observe and document this effect. His telescopic observations of Venus led him to realize that planets orbit the sun—not the earth. This was in contrast to the prevailing scientific view of the day. The earth-centered (geocentric) solar system predicts that Venus will only appear as a crescent. The sun-centered (heliocentric) model can make sense of the phases of Venus and their correlation with its apparent size.

Finally, the phases of Venus (and Mercury) are reversed relative to the moon. In other words, when the moon is illuminated on the right side (toward the western horizon), it is in a waxing phase and will appear more illuminated on the following night. But when Venus is illuminated on the right side, it is in a waning phase and will appear less illuminated over the following weeks. Both Venus and the moon orbit in the same direction. So how can this be? The difference is because Venus orbits the sun, whereas the moon orbits Earth. So when the moon is in-between Earth and the sun, it is moving to the left (eastward). But when Venus is in between the sun and Earth, it is moving to the right (westward).

From our perspective on Earth, Venus stands out as a pure white light, superior in splendor and luminance. Venus is mentioned in Scripture as the “morning star,” where its brilliance is used as a symbol for Christ (Revelation 2:28; 22:16).12 None of the other nighttime stars can compete with Venus, so it is a fitting symbol of the beauty and glory of our Lord.

References

  1. Venus is the second-brightest regular object in our night sky. Only the moon is brighter.
  2. Venus is not a star in the modern sense of the word. However, the ancient term for star (aster in Greek, kowkab in Hebrew) includes both stars and planets. A planet is a “wandering star”—a star that moves relative to the majority of fixed stars.
  3. Venus is 95 percent as large as Earth in diameter.
  4. Though they do have the same Father (James 1:17), they cannot be “twins” because Earth is three days older than Venus (Genesis 1:1, 14-19).
  5. Krassilnikov, A. S. and J. W. Head. 2003. Novae on Venus: Geology, Classification, and Evolution. Journal of Geophysical Research: Planets (1991-2012). 108 (E9): 1-48.
  6. Coronae are found only on Venus and Uranus’ moon Miranda.
  7. See the Mercury article for a discussion of sidereal versus solar days: Lisle, J. 2013. The Solar System: Mercury. Acts & Facts. 42 (8) 10-12.
  8. This is relative to the North Pole of the solar system. Alternatively, we could define the North Pole of a planet as the pole under which the planet rotates counterclockwise. By this definition, all planets rotate in the same direction and Venus is merely “upside down.” There is no physical difference between Venus being tilted 3° and rotating backward (clockwise), as opposed to Venus being tilted 177° and rotating forward (counterclockwise). Both conventions are used in astronomy.
  9. Since the planet Uranus is tilted 97°, it too could be considered a backward-rotator with a tilt of 83°. However, since this is nearly a right angle, it makes little difference.
  10. The outer planets can only be seen in gibbous and full phases. This is because quarter and crescent phases require the planet to be closer to the sun than the observer is. This can never occur for an outer planet as seen from Earth.
  11. This effect is also visible in the planet Mercury for the same reason. However, the effect is much less noticeable on Mercury since its distance from Earth does not vary as much. Also, Mercury is much smaller than Venus and closer in angle to the sun, making observations of its apparent diameter far more difficult.
  12. In some English translations, Lucifer is called the morning star in Isaiah 14:12. It may bother some people that the same symbol is used for Christ, but Isaiah 14:12 may simply indicate that Lucifer was one of the most glorious angels before he rebelled. Satan attempts to parrot Christ in some ways—Christ is the Lion of Judah (Revelation 5:5), and Satan prowls about as a roaring lion (1 Peter 5:8). We note that the word “star” does not appear in the Hebrew text of Isaiah 14:12. “Son of the morning” or “son of the dawn” appears to be a more literal translation from the original text.

* Dr. Lisle is Director of Research at the Institute for Creation Research and received his Ph.D. in Astrophysics from the University of Colorado.

Cite this article: Lisle, J. 2013. The Solar System: Venus. Acts & Facts. 42 (9): 10-12.


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