Backyard Astronomy: summer heatwaves

July and August are generally considered the hottest months of the year in Canada. Nights can be hot and stuffy, making it difficult to sleep without air conditioning. One term you may have heard to describe this hot season is “heatwave day of summer”. It begins the first week of July and can last a few months. But where does this saying come from and what is the meaning behind it?

The idea is derived from the early Greeks and Romans who used the canine star – Sirius – as part of their reasoning. Sirius is only 8.6 light years away and is the brightest star in our night sky, as seen on cold winter nights. However, at this time of year, both Sirius and the sun are rising at the same time – sort of. It was believed that Sirius combined with the sun produced additional heating hence its name.

Due to its proximity to us, the radiation generated by the sun travels through space and heats molecules in the Earth’s atmosphere. The stars we look at at night, including Sirius, are far too far away for us to feel the effects. Right now, Sirius is still lost in solar glare, but the star will begin to reveal itself by the end of August in the southeastern sky before dawn. During the year, the stars rise four minutes earlier each night than the day before. This is why we see different constellations rising month after month.

There are very rare instances where a planet like Earth can feel the effects of a distant star. Gamma rays are the brightest electromagnetic explosions that occur and can cause problems for neighboring planets with an atmosphere less than 6000 light years away. Gamma rays are produced in the cataclysmic end of a massive star when it is torn apart by a gigantic explosion called a supernova. The collision of two neutron stars can also produce these lethal rays which shoot out in a straight line from either the star’s two poles or from the collision. As if looking at the barrel of a rifle, the beam must be pointed directly at a planet to wreak havoc on this distant world and on life if it exists.

Some scientists have speculated that a narrow beam gamma ray lasting only 10 seconds struck Earth about 440 million years ago from a star a few thousand years away- light. Keep in mind that a light year is almost 10,000 billion kilometers long. It is believed that this led to the Ordovician Extinction, the second largest of the five extinctions the earth endured. Back then, there were no creatures that walked or flew on earth. A flurry of marine life appeared in the oceans during the Cambrian Explosion around 540 million years ago.

When the proposed gamma rays hit our world, they caused the planet to lose half of its protective ozone layer and subjected the earth to intense solar radiation. This led to an Ice Age and the Extinction of the Ordovician where around 85 percent of saltwater species perished due to the drop in water temperature, especially in tropical waters.

The cosmos is not a boring place where the stars just shine. Violent off-scale events occur on a much slower timescale with the possibility of disastrous life-changing consequences in worlds far away thousands of light years away. So far we are safe from such life changing events, however, the universe likes to curve a ball at us every now and then.

See you next time, clear skies.

Known as “The Backyard Astronomer,” Gary Boyle is Professor of Astronomy, Guest Lecturer and Monthly Columnist for the Royal Astronomical Society of Canada. He has been interviewed on over 50 Canadian radio stations as well as on television in Canada and the United States. In recognition of his public awareness of astronomy, the International Astronomical Union honored him by naming him Asteroid (22406) Garyboyle. Follow him on Twitter @astroeducator or visit his website www.wondersofastronomy.com.

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