Cold, dark nights spell joy for stargazers
Dark sky, cold sky. Those are the magic words that stargazers love to hear. Winter nights can be bitter cold, but the chilliest nights usually offer the best viewing of the celestial sky. Stars and planets dance across the black dome of the sky and give us a front row seat to the workings of the solar system and the universe. The toughest part for us is braving the cold and keeping warm. The challenge is often worth it.
A dark sky is one that doesn't suffer from the interference of city lights. Not everyone has this view, of course. The outlying counties and rural locations give the viewer a breathtaking view of the night sky from horizon to horizon. But that doesn't mean people living close to the city can't see a thing. Brighter stars and planets, as well as the moon, are visible just about everywhere in the city. The dim and subtle features of the night sky require darkness.
A cold sky is easy to find this time of year. Cold air is dry air, and the less moisture in the lower atmosphere means there is less interference between our eyes and whatever we are looking at in the sky. No wonder the great observatories of the world place their huge telescopes on mountain tops. Higher altitude, even in tropical climates, means drier air, less moisture, and better seeing.
So what do we have to look forward to in the night sky over the next few weeks? There is the parade of planets, which tend to be brighter than most stars in the sky. And planets tend to twinkle very little or not at all. They are a solid body that is reflecting sunlight.
Stars are pinpoints of light from light-years away. Their light is "roughed up" by the variations in atmospheric density as it meets our eyes. So they appear to twinkle. Some bright stars near the horizon twinkle so much that you see all the colors of the rainbow rotating in appearance: red, green, blue, yellow, etc.
The planet Saturn is the star of the evening sky this month. It reaches opposition and closest approach to Earth on December 17. Opposition means it is directly opposite the Earth from the Sun, so it typically reaches a point directly south of us around midnight.
On the 17th it will be 750 million miles from Earth, but a good pair of binoculars or a small telescope will reveal the famous rings surrounding Saturn. Don't miss the night of the 18th and 19th when the Full Moon passes just above Saturn. Weather permitting, it should make for a glorious sight.
Saturn is the second largest planet in our solar system, but the Big Kahuna, Jupiter, is a sight for the sky after midnight. The largest planet orbiting our Sun rises around 9 p.m. and by 11 it is a beacon of brightness in the eastern sky. By 4 in the morning, mighty Jupiter is high in the southern sky just as the pair Venus and Mars rise low in the east. Venus is by far the brightest object in the sky except for the Moon and the Sun.
This planet, often called the twin of Earth because its size is similar to our planet, is covered in clouds of carbon dioxide. Volcanic eruptions and lack of water vapor have built up the atmosphere to produce a runaway greenhouse effect, with Venus' surface temperature estimated at 900 degrees Fahrenheit! Those bright clouds that surround Venus reflect a tremendous amount of sunlight. Venus is also closer to us than any other planet so it appears the brightest.
Mars is known as the Red Planet, and indeed it has a reddish hue as it rises next to Venus in the early morning sky. The Moon passes close to Venus and Mars on the mornings of the 29th and 30th. A clear, cold sky will reveal quite a sight before sunrise. There are some major advantages to those who are awake and outside before dawn this time of year!
Finally there is a meteor shower to check out this month. The Geminid meteor shower is set to peak on the night of December 13-14, although best viewing will be high in the southern sky between 2 and 5 a.m. Start looking for them as early as December 11th and as late as December 15th.
The radiant, or the section of the sky from which they appear, is located in the constellation Gemini the Twins, directly between the bright planets Saturn and Jupiter. The Geminids are different than most meteor showers in that they may result from the passage of an asteroid instead of a comet. The object 3200 Phaethon travels in a 1.4-year-long extremely elliptical orbit around the Sun.
Dust and debris from this rock passes through the Earth's atmosphere to provide the meteor shower. Astronomers are still debating whether Phaethon is asteroid or comet. Either way, bundle up after midnight on the 14th and hopefully catch up to 75 meteors per hour under ideal sky conditions. You know: cold sky, dark sky.
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