Night Watch

Updated 1 January 2015

The January night sky brings with it a plethora of bright stars and planets. The summer Milky Way stretching north to south, is peppered with stars with exotic names such as Procyon, Aldebaran, Betelgeuse, Canopus. These stars and many others provide the summer night sky with a sparkling quality that forever draws us to look up in awe.

Low in the north-eastern sky, Castor and Pollux are visible. They form the heads of the twins of Gemini. In ancient Roman legends, the twins represent Romulus and Remus, the legendary founders of Rome. To the naked eye, Castor appears as a single star, through a moderately sized telescope, it transforms into three stars. Further investigation has revealed that each of the three main stars, is in turn a double star! Castor then consists of 6 stars all orbiting around a common centre of gravity.

Pollux, on the other hand is nowhere near as interesting as Castor. It's a yellow star, about 11 times the diameter of our Sun, and 35 times as bright.

For a contrast in star colours, aim your telescope or binoculars at Rigel, much higher in the sky. It is a blazing white-hot star of intense brilliance and dazzling beauty. Its surface temperature is about 12,000 degrees (our Sun's is 4,500 degrees), and its energy output exceeds that of our Sun by a factor of many thousands; it’s something like 57,000 times the brightness of the Sun! If we placed our Sun at the reputed distance of Rigel (900 light years), then the Sun would be totally invisible to the naked eye and most binoculars.

Just below Rigel is one of the most remarkable astronomical objects in the evening sky. It is known as the Orion Nebula or M42. To the eye alone, the nebula looks like a big but faint star. But its true nature is far more impressive. Instead of a single star, it’s a stellar nursery, a light-years-wide complex of gas and dust that’s given birth to thousands of stars.

Many of the stars are less than a million years old, with some just a few tens of thousands of years old. Some of the youngest are also the hottest and most massive. Strong “winds” from these stars compress some of the nearby clumps of gas, causing them to collapse and form new stars. But the winds also blow away some of the gas and dust, preventing stars from taking shape.

In addition to the big boys, the nebula also contains thousands of smaller, fainter stars, plus the “failed stars” known as brown dwarfs. And many of the stars are encircled by disks of gas and dust — the raw materials for planets.

And there’s still plenty of gas and dust for making more stars. These giant clouds and streamers can stretch across light-years of space. Some of them glow like fluorescent bulbs, energized by the radiation from hot stars, while others reflect the light from the nebula’s crowded stars. The remarkable glow of this busy stellar nursery is what draws every skywatcher to it.

Nearly a third of the way up the northern evening sky we see a small yet enticing knot of glittering stars. This is the Pleiades star cluster, also known as the Seven Sisters - though only 6 stars stand out overtly to the unaided eye. (The star representing the seventh sister does not shine as brightly because, according to star lore, she married a mere mortal.) Binoculars, of course, show dozens of stars not visible to the unaided eye.

The Pleiades have played a prominent role in ancient mythology.  Almost every culture has a story relating to these stars. For example, the ancient Aztec and Maya Indians, considered the midnight culmination (when they have reached their highest point in the sky) of the Pleiades a significant and ominous event tied in with the creation and destruction of the world. Today, the Subaru car maker uses the Pleiades as its logo.

The “evening star” is a dazzling sight in the western sky. It appears soon after sunset, and you shouldn’t have any trouble picking it out, because it far outshines all the other planets and stars in the night sky. This brilliant beacon is Venus, our closest planetary neighbour. It passed behind the Sun from Earth in November, and is now getting closer to us in its smaller, faster orbit around the Sun. On January 1, it will be 241 million kilometres from Earth. By the end of the month, that distance will have shrunk to 225 million kilometres. By the time Venus catches up with Earth in June 2015, that distance will be a mere 110 million kilometres.

Venus’s phases were discovered by the Italian astronomer, Galileo Galilei. He was the first to turn a telescope toward the heavens. Among other wonders, he saw that Venus went through a cycle of phases, just as the Moon does. His discovery confirmed that Venus orbits the Sun, placing our star at the centre of the solar system instead of Earth.

In the opposite part of the sky, and a little later in the evening, another brilliant “star” makes its presence known. Low in the north-eastern sky, you’ll find the colossus of the planets, Jupiter. Hydrogen makes up about 70 percent of Jupiter’s mass. In the planet’s upper atmosphere, it combines with other elements to make water, ammonia, and other compounds.

Hydrogen is the simplest and most common chemical element; it makes up most of the “normal” matter in the universe. When it is squeezed tightly in the heart of a star, it starts nuclear fusion, and makes the star shine. And in the hearts of giant planets, like Jupiter, hydrogen forms a metal. Currents within this dense liquid can generate magnetic fields that extend hundreds of millions of miles into space.

As you move deeper into Jupiter, gravity compresses the hydrogen to form a liquid. And as you move deeper still, the electrons and protons in the hydrogen atoms separate, producing a layer of metallic hydrogen that’s thousands of kilometres thick.

Jupiter’s fast rotation creates strong eddies and streamers within this layer, generating electrical currents. That creates a magnetic field that’s thousands of times stronger than Earth’s.

The Moon is Full on January 5th at Last Quarter on the 13th, New on the 20th, and at First Quarter on January 27th