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)