Venus is the second-closest planet to the Sun, orbiting it
every 224.7 Earth days. It is the brightest natural object in the night sky,
except for the Moon, reaching an apparent magnitude of −4.6.
Because Venus is an inferior planet, from Earth it never appears to
venture far from the Sun: its elongation reaches a maximum of 47.8°.
Venus reaches its maximum brightness shortly before sunrise or
shortly after sunset, for which reason it is often called the Morning Star
or the Evening Star.
Classified as a
"sister planet", for the two are similar in size, gravity,
and bulk composition. Venus is covered with an opaque layer of
highly reflective clouds of sulfuric acid, preventing its surface
from being seen from space in visible light; this was a subject
of great speculation until some of its secrets were revealed
by planetary science in the twentieth century. Venus has the densest
atmosphere of all the terrestrial planets, consisting mostly
of carbon dioxide, as it has no carbon cycle to lock carbon back into rocks
and surface features, nor organic life to absorb it in biomass.
It has become so hot that the earth-like oceans the young Venus is
believed to have possessed have totally evaporated, leaving
a dusty dry desertscape with many slab-like rocks. The evaporated
water vapor has dissociated and hydrogen has escaped
into interplanetary space. The atmospheric pressure at the planet's surface
is 92 times that of the Earth, the great majority of it carbon dioxide
and other greenhouse gases.
Venus's surface has been mapped in detail only in the last 20 years
(Project Magellan) which listed about a thousand meteor craters,
a surprisingly low number compared to Earth. It shows evidence
of being geologically very young with extensive
in the atmosphere is taken by some experts to show many of its volcanoes
are still active today, but it is an enigma as to why no evidence
of lava flow accompanies any of the visible caldera.
The adjective Venusian is commonly used for items related to Venus,
though the
the now-archaic Cytherean is still occasionally encountered. Venus is
the only planet in the Solar System named after a female figure,
although two dwarf planets—Ceres and Eris—also have female names.
Venus is thought to undergo periodic episodes of
in which the crust is subducted rapidly within a few million years,
separated by periods of a few hundred million years of relative stability.
This contrasts strongly with Earth's more or less steady state
of ongoing subduction and continential drift, but the venusian behavior corresponds well with Earth modeled then changed by removing
the lubricant—the oceans. It is believed the surface rocks of
Venus are only about a half-a-billion years old as impact crater analysis
suggests that its surface dynamics have exchanged its surface
for a clean face (wiping out old craters) sometime in the last billion years.
Vocabularies
1. orbit - ทางโคจรของดวงดาว , จักรราศี
2. apparent - ปรากฏ
3. elongation - ยาวเรียว , ต่อ , ยืด
4. Classified - จำแนกแยกแยะไว้แล้ว
5. terrestrial - บนพื้นโลก
6. opaque - อับแสง , ขุ่น , ทึบ
7. consisting - ประกอบด้วย
8. absorb - ดูด , กลืน , ระงับ
9. dissociate - แยกตัวออก
10. dioxide - ธาตุ
11. greenhouse gases - ปรากฏการณ์เรือนกระจก
12. meteor - สะเก็ดดาว
13. enigma - ปริศนาที่ลึกลับ , ลึกลับ
14. evidence - ชัดแจ้ง , อย่างเห็นได้ชัด , เด่น , ปรากฏ
15. dwarf - แคระ
16. tectonics - เกี่ยวกับการเปลี่ยนแปลงของผิวโลก
17. separate - แยกกัน , ห่างกัน
18. stability - มั่นคง , เสถียรภาพ
19. continental - เกี่ยวกับทวีป
20. lubricant - วัตถุสำหรับหล่อลื่น
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