|
est and second-brightest orbs of nighttime - the moon and Venus, respectively - pairing up in the eastern predawn and dawn sky.
Everyone with a clear sky and an unobstructed eastern horizon will be able to see the morning attraction before sunrise tomorrow. The rising time of the moon and Venus, however, will vary around the world. At mid-northern latitudes, the moon and Venus will rise about three hours before the sun, whereas at middle latitudes in the Southern Hemisphere, the twosome will come up roughly an hour before sunrise. Near the equator, the moon and Venus will climb into the sky about two hours before sunup.
Looking for a sky almanac? EarthSky recommends
There are several reasons why Venus shines so brilliantly in our sky. Venus is second-closest planet to the sun - after Mercury - so the intensity of sunlight hitting Venus is greater than for more distant planets. Also, Venus' orbit is the closest to Earth's orbit. Plus, Venus' cloud cover reflects a greater percentage of its incoming sunlight than that reflected by any other solar system planet.
Venus' cloud cover hides this planet's surface features, so it's difficult for astronomers to measure its rotation period. Some 16 years ago, the Magellan spacecraft used radar to determine that a single rotation (relative to the backdrop stars) is 243.0185 Earth-days long. Recently, the Venus Express satellite used infrared wavelengths to find that Venus' rotation period has slowed down by 6.5 minutes.
Has a mistake been made or is Venus' spin really slowing down? Undoubtedly, (Continued on page 15)
|
|
