Guide to galaxy for Earth Hour's starry, starry night

March 18, 2009

(PhysOrg.com) -- When cities turn off their lights for Earth Hour their occupants will get more than a warm and fuzzy green feeling, they will also see stars hundreds of trillions kilometres away lighting up a moonless night sky in all its glory.

QUT senior lecturer Dr Stephen Hughes said if large numbers of people switch off their lights, the stars promised to be as bright and clear as they are in places far away from city lights.

"It is an added incentive to turn off the lights during Earth Hour because it will be like turning the clock back to a time when Brisbane was very much smaller," Dr Hughes said.

"During Earth Hour you will be able to see the mighty constellation of Orion about 25 degrees above the western horizon with a line of three stars known as Orion's belt.

"Just to the left of the belt is the sword of Orion, a diagonal group of three stars whose central star is a fuzzy patch known as Orion Nebula. The fuzziness is actually a vast ocean of gas and dust where new stars are forming.

"To the right of Orion's belt you will see a bright red star called Betelgeuse (pronounced beetlejuice) which is a type of star known as a red giant with a diameter more than 1000 times greater than the sun.

"Betelgeuse is so huge if it were where the sun is, its outer surface would encompass the orbit of Jupiter 750 million kilometres away.

"On the left of Orion's belt you will see a bright blue star called Rigel - this is a blue, supergiant 17 times bigger and 40,000 times brighter than our sun. Rigel's surface temperature is 11,000 degrees.

"Sirius, the brightest star in the sky, sits more or less in a line above Orion's belt. Ancient Egyptians looked for Sirius, the white star, to herald the start of the annual flooding of the Nile. Sirius is relatively close because it is only 8.6 light years away. A light year is about 9.5 trillion kilometres."

Dr Hughes said the multi-ringed planet Saturn will be about 45 degrees above the eastern horizon on March 28.

"Although Saturn is famous for its beautiful rings, 2009 is not a good year to view it because the rings are almost side on to the earth and so will appear as a faint line. You will need a small telescope to see the rings.

"But the magnificent Southern Cross will be on display. This can be found by locating two bright stars, Alpha and Beta Centauri, which point to the Southern Cross. Alpha Centauri (the one farthest from the Southern Cross) is the closest star to the sun and is actually made up of three stars - two similar to our sun and one called a red dwarf named Proxima Centauri.

"Next to the star in the Southern Cross which is closest to Beta Centauri is a wonderful cluster of stars known as Herschel's Jewel Box - get your binoculars out for this one and you will see a spectacular sight.

"If enough lights are turned off and it is very dark you may see a patch of sky with no stars on the point of the Southern Cross. This is a cloud of gas and dust called the Coal Sack which is 600 light years away and obscures our view of the centre of the galaxy.

"When your eyes have adjusted you will see more in the sky especially the Milky Way which looks like a wispy band of cloud arching across the sky from south east to north west.

"You will see stars towards the centre of our galaxy about 28,000 light years away. They are so far away we cannot see individual stars, only billions of stars in the aggregate.

"It's like sand on a beach - you can't make out individual grains until you pick up a handful. The amazing thing is that there are probably mores stars in the universe than grains of sand on the beaches and deserts of the earth."

Dr Hughes said an excellent resource for seeing what's up in the Brisbane night sky is a shareware program called Stellarium downloadable from www.stellarium.org .

Provided by Queensland University of Technology (web)