Sirius

Sirius A and B (Artist's impression, Wikipedia)

Last week had some of the best night skies we’ve had for a long time, and we should have them for a few days yet. The Moon brightens the evening sky this week, waxing from crescent to gibbous phase as she dives toward the southern reaches of the ecliptic.

Tonight the moon forms an attractive grouping with the golden-hued planet Saturn and the blue-tinted star Regulus. By the end of the week she is closing in on the bright star Spica, one of the signature stars of the springtime sky.

The April sky presents a time of transition from the bright beacons of the winter to the rising constellations of the summer sky. Early in the evening, near the end of astronomical twilight, the bright stars of the Great Winter Circle prepare to wink out over the western horizon. By 10:30 pm the familiar pattern of Orion is setting, and to the southeast the brightest of the night time stars, Sirius, hangs about 10 degrees above the southwest skyline. When it’s this close to the horizon, the bright light of the star must pass through the densest concentration of our atmosphere, with all of its attendant currents, temperature inversions, and dust. The star appears to jump around and cycle randomly through all the colours of the visible spectrum. Jumpy Sirius is one of the most widely reported “UFO” sightings.

Some objects don’t twinkle at all. Since planets are appreciable discs, as opposed to stellar pinpoints, the atmosphere doesn’t affect their light-paths as strongly. One of these worlds is Mars, which is now trekking across the stars of Gemini. The red planet is closing in on the brighter of the Gemini twin stars, Pollux, and he closely matches the star in brightness. Over the next few weeks Mars will march right out of Gemini, and by the early summer he’ll be bearing down on Saturn. If you can find Orion from last week, Gemini is just up a little and to the left. Check the diagram Betalgeuse is part of Orion's bow.

Mars moving through Gemini (BBC)

Saturn himself is hanging around the bright star Regulus in Leo. He is now perfectly placed for viewing, crossing the meridian at around 10:00 pm. Tonight he entertains the waxing Moon, and there are few celestial sights more captivating to the small telescope user than these two worlds. Where Luna shows endless battered landscapes, Saturn shows a small serene disc encircled by the planets mysterious rings. Take advantage of the two while they are within hailing distance of each other.

Jupiter is still best seen in the pre-dawn hours. He’s located in the thick of the stars of summer, low in the southeast as morning twilight gathers. His turn in the evening sky will come, and he’ll shine against a backdrop of the great star clouds of the summer Milky Way.

And we’ve lost mercury and Venus behind the sun for a little while yet, but Mercury will be back bright in the evening twilight by the end of the month.

If you’re hopelessly confused and don’t know where to look, take a look at the star charts on the radio Scilly website, under Scilly stars or use Google sky. If that fails then you’ve probably forgotten to go outside.

(BBC)

Outlook for April and Star Maps

Outlook for April and Star Maps. Source BBC.

Mercury moves under the daytime Sun on the 16th, an event known as the superior conjunction. By the end of the month it has made its way out of the glare to become an evening object. Look low and to the northwest around 9pm from the 26th to catch this elusive world, it will be the 'star' sitting below the Pleiades or Seven Sisters group.

Venus is unobservable this month as it closes in on the Sun.

Mars is currently riding high in the spring night sky. The planet will cross most of Gemini, the Twins, through the month, and will almost make it into Cancer, the Crab.

Jupiter rises just after 3am during the middle of the month, but because of its location in the constellation of Sagittarius, the Archer, it won't be that high in the sky by dawn. However, it will be incredibly bright at the end of the month with a magnitude of 2.4. On the morning of the 27th you'll find the waning gibbous Moon sitting under Jupiter, and as long as your southern horizon is fairly good then the planet will be unmistakable.

Saturn is visible all evening, from its starting place high up in the southwest sky at sunset. Currently, Saturn is in Leo, the Lion, where it will stay until September 2009. The real star to the right of the planet throughout the month is the slightly bluish Regulus, the leading star of the Lion. The waxing gibbous Moon sits below Saturn on the 15th.

Meteor Showers

The 'shooting star' displays include the April Lyrids from the constellation of Lyra, the Harp. The peak of this shower is on the 22nd when you could see a maximum of about 15 meteors an hour. However, the Moon is just past full which will make it nigh on a complete waste of time looking.

ORION

Orion (www.freewebs.com)

This week I’m going to bang on about Orion, the constellation which completely dominates the SW sky at the moment, hanging over St Agnes and the Western Rocks. But not for long - as we get closer to mid summer, it will sink lower and lower towards the horizon until we lose it altogether. Orion is the one of the largest and certainly the most beautiful of the constellations and contains a large number of intriguing deep space objects.

Orion The Hunter, is a prominent constellation, one of the largest and perhaps the best-known and most conspicuous in the sky. Its brilliant stars are found on the celestial equator and are visible throughout the world. Its three prominent "belt" stars - three stars of medium brightness in the mid-section of this constellation - make it easy to spot and globally recognised.

According to the most common contemporary imagery, Orion is standing next to the river Eridanus with his two hunting dogs Canis Major and Canis Minor, fighting Taurus the bull. Other prey of his, such as Lepus the hare, can be found nearby.

There are other contemporary names for Orion. In Australia, the belt and sword of Orion are sometimes called the Saucepan, because the stars of Orion's belt and sword resemble the kitchen utensil as seen from the Southern Hemisphere. Orion's Belt is called Drie Konings (Three Kings) by Afrikaans speakers in South Africa. The appellation Driekoningen (the Three Kings) is also often found in 17th and 18th-century Dutch star charts and seaman's guides.

Historically, it has had other names, perhaps the earliest known being the Babylonian "Shepherd of Anu", corresponding to an apparent representation of the constellation Auriga or an element of it, as a shepherd's crook.

The Horsehead Nebula, pictured by Hubble. (NASA)

Besides these nebulae, surveying Orion with a small telescope will reveal a wealth of interesting deep sky objects, including M43, M78, as well as multiple stars including Iota Orionis and Sigma Orionis. A larger telescope may reveal objects such as Barnard's Loop, the Horsehead Nebula, as well as fainter and tighter multiple stars and nebulae.

Star formation in Orion in infrared by Spitzer Space Telescope.(NASA)

All of these nebulae are part of the larger Orion Molecular Cloud Complex which is located approximately 1,500 light-years away and is hundreds of light-years across. It is one of the most intense regions of stellar formation visible in our galaxy.

• Orion Cloud Complex
• SEDS website
• Clickable table of Messier Objects
• Orion images