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What is the Summer Triangle?


Lorraine Hanlon, UCD School of Physics.

Lorraine Hanlon, UCD School of Physics.

Lorraine Hanlon, UCD School of Physics.

One of the celestial highlights of our short summer nights is the so-called 'Summer Triangle', made up of three bright stars called Vega, Deneb and Altair, in the constellations Lyra, Cygnus and Aquila, respectively.

Although they are associated with different constellations in the night sky, their brightness, even against the backdrop of the relatively bright summer night sky, makes this stellar arrangement, or 'asterism', an easy spot.

Looking to the east after sunset at this time of year, the first star to reveal itself is the dazzling Vega, the apex of the triangle. Altair is to the lower right, with Deneb to the left. Far away from light pollution, you might see the band of our galaxy, whose 'Via Lactea' ( Milky Way) runs through the Summer Triangle.

Vega, at a distance of about 25 light years, is an important star for astronomers, who use it as a reference point for the 'magnitude' brightness scale. An asteroid belt around Vega has recently been discovered and it may harbour a solar system with rocky planets.

Altair is a little closer to us than Vega, while Deneb has been estimated to be about 1,550 light years away. It is a blue super-giant and about 20 times the mass of our sun. If Deneb was in our solar system it would extend past the radius of Earth's orbit.

All three stars have a blue-white appearance, indicative of similar surface temperatures of between 7,200 and 9,200 oC. Of course, their nuclear cores are much, much hotter - unlike our Irish summer.

In the western sky at dusk watch out for the spectacular sight of Venus and Jupiter as they draw closer together through June, with their closest approach happening on June 30/July 1.

Irish Independent