The crisp autumn evenings of April offer an ideal opportunity to explore the majesty of the southern sky. Go find yourself a nice dark spot in the back-garden, and let your eyes become accustomed to the darkness. Notice how many more stars you can see, even after a few minutes, as the pupils of your eyes expand to let as much light in as possible.

With dark adapted eyes, scan the area along the Milky Way from the Southern Cross to Sirius. The way will be sprinkled with a variety of stars, clusters and nebulae for you to observe.
Over to the north, the constellation of Leo, the lion is quite prominent. Many different cultures have seen a lion in this pattern of stars. But others have seen a sickle, which forms the lion's head and shoulders, and a small triangle, which forms its hindquarters. The heart of the lion is close to the Moon on the evening of April 8. The bright star that marks the lion’s heart is Regulus. You’ll find it above the 10-day old Moon.

Regulus is impressive. It’s a system of four stars, but only one shines bright enough to see in a small telescope. Known as Regulus A, it is almost four times the Sun’s mass, and more than 300 times the Sun’s brightness.

But the Moon is even closer to another star of Leo that is more impressive. Eta Leonis is just below the Moon. Because of the Moon’s brightness, you may want to use a pair of binoculars to locate it, or just wait a couple of nights until the Moon moves away from that part of the sky. It looks fainter than Regulus. That’s because Eta Leonis is much farther than Regulus — about 1800 light-years, versus only 79 light-years for Regulus.

In fact, Eta Leonis is among the biggest and brightest stars in the galaxy. Studies show that it’s about 10 times heavier than the Sun, about 50 times wider, and about 20 thousand times brighter.
Eta Leonis is only about 25 million years old, compared to four and a half billion years for the Sun. But thanks to its great mass, the star is near the end of its life. Within a few million years, it’s likely to explode as a supernova. For a while, it will greatly outshine every other star in the galaxy.

To the right of Leo is the constellation of Virgo. It is in that apparently vacant part of sky between Leo and Virgo, that we find the Virgo Cluster of Galaxies. A telescope will reveal dozens of galaxies. Each one is home to anywhere from a few million to hundreds of billions of stars. Using data obtained with the Hubble Space Telescope, astronomers now estimate that the distance between Earth and the centre of the Virgo Cluster is some 48 million light years. That means that the light left the galaxies 48 million years ago, travelling at a speed of 300,000 kilometres per second!

As we turn our attention to the south-eastern part of the sky, the Southern Cross (Crux on the map) is not difficult to pick out. More a telescopic object, than for binoculars, the Jewel Box star cluster (also known as NGC4755) not far from the Southern Cross, cannot be beat for pure splendour. It earned its name because it reminds observers of spying at a lady's collection of precious stones against black velvet. The many coloured stars make this object a definite tourist destination.

Just above the Southern Cross, the Milky Way is at its brightest. It’s here that we find a large cloud of gas and dust, known as the Eta Carinae Nebula (labelled 3372 on the chart).

The nebula (Latin for cloud) is a vast cloud of gas and dust, about 7300 light-years away in the constellation Carina, that's given birth to more than 60 hot, heavy stars. And one of those stars is the star that gave the nebula its name. Eta Carinae is a fascinating object. It first attracted attention in the mid 1800s, when it flared to several hundred times its normal brightness, becoming one of the brightest stars in the sky for a brief period of time. The instruments of the day couldn't reveal any detail around the star, so astronomers couldn't make much sense of what was happening.

But modern telescopes reveal an impressive sight. The flare-up was caused by a massive eruption from the star's surface. It surrounded Eta Carinae with a turbulent cloud of gas and dust that looks like an hourglass. Recent observations suggest that Eta Carinae may consist of 2 stars, which are hidden inside the cocoon. One star could be about 30 times as massive as the Sun, and the other about 80 times as massive. The stars produce violent "winds" of gas. As the winds ram into each other, they produce X-rays. The X-rays are most intense every five and a half years, suggesting that is how long it takes the two stars to orbit each other.

Get your last look at the giant planet Jupiter this month before it is swallowed in the glare of the setting Sun. This is the biggest planet in our solar system, almost 10 times the diameter of Earth! And yet, it spins on its axis in just 10 hours. That’s really moving. Because of this fast spin, anyone observing with a telescope, can see features on the cloud tops of Jupiter change their position over a short period of time. Its 4 large moons, Io, Europa, Ganymede and Callisto are all easy to see, even in binoculars. Find it low in the north-west soon after sunset.

It’s Jupiter’s large size and mass, that has enabled NASA to use it to propel spacecraft to the outer reaches of the solar system. The planet itself is a big envelope of gas wrapped around a small solid core. Most of the gas consists of hydrogen and helium. The hydrogen would make a good energy source for rockets. But it’s so far below the clouds that it would take more energy to go down and get it than you’d gain from the hydrogen itself.

Instead, spacecraft get their “boost” in the form of gravitational energy. As a craft approaches Jupiter, it is accelerated by the giant planet’s gravity. How much acceleration depends on how close it gets to the planet, a closer approach provides a more powerful “kick.” Craft have used that kick to reach Saturn, Uranus, Neptune, and Pluto, and to loop above the Sun’s poles. These craft “stole” momentum from Jupiter, giving Jupiter an equal kick in the opposite direction. But since Jupiter is so much heavier than any spacecraft, no one will ever notice the difference.

The Moon is at First Quarter on April 5th, Full on the 13th, at Last Quarter on the 21st, and New on April 28th.
Happy observing!

Above: A splendid vista awaits on the evening of April 2. About 30 minutes after sunset, look low into the pastel glow of the western sky. You’ll see the thin crescent of a 4 day old Moon, with the orange star Aldebaran and the Hyades
star cluster just above it, and brilliant Jupiter further to the right. What a photogenic scene it will be! Using binoculars or a telescope follow Jupiter’s 4 largest moons as they perform their merry dance around the giant planet. You can see a change in their positions in less than an hour, even from a whopping 820 million kilometres!