The Summer Triangle – part 1

The night sky is a collection of patterns known as asterisms which, when connecting the dot (stars) takes on the shape of objects, people, and animals. The larger boundaries of each asterism make up the individual constellations. The summer triangle is the connection of three bright stars from three completely different asterisms. To the far left, we have the star named Deneb or the tail of Cygnus the Swan. Deneb is a spectral class A2 star and estimated to be 3,200 light-years from us. This magnitude 1.25 blue-white supergiant star is the 19thbrightest star in the night sky and is one of a few seen from this great distance with the unaided eye. Deneb is 110 times the size of our sun. So with the sun being 109 times the size of our planet, you can line up almost 12,000 Earths side by side across the belly of Deneb. Now that is big.

Next, we come to Vega – the alpha star of Lyra the Harp. At just about magnitude 0.0, Vega is the brightest of the trio. Like Deneb, Vega is roughly the same spectral class and takes on the bluish-white colour. But this star is nowhere near Deneb’s grand distance as it is only 25.3 light-years from us. But it does spin at a staggering 274 km/sec thus making it bulge slightly at its equator. Another unique factor is Vega appears to have a disk of dust something like our Keiper Belt. There are also suggestions that a Jupiter sized planet might orbit Vega.

And last but certainly not least is the final link of the triangle – Altair is also known as the ‘sweet sixteen star’. It is so named because of its close distance of 16 light-years to us. So if you are 16 years old and reading this article, the light you see tonight left Altair around the time you were born. Just like its group members, Altair is a white star with a spectral type A7. It is 1.8 times the size of the Sun and spins at 210 km/sec on its axis meaning it rotates once every 9 hours. This causes the equator to bulge out thus causing the equator to measure 20 percent greater than the pole to pole diameter. As a reference, Sun rotates at a mere 2 km/sec.

Parked just outside and to the east of Deneb is an emission nebula that spans four full moons. Commonly called the North American nebula because of its uncanny resemblance to our continent, NGC 7000 is also teamed up with the Pelican nebula, named for the same reason. Both objects are part of the same stellar cloud of gas and dust that is producing stars. It just so happens, a dark molecular cloud is positioned between NGC 7000 and Earth thus obscuring certain areas. Visual observations of the North American might be a challenge so astrophotography would be the way to go.

Chart 1

From Deneb, move along the Milky Way to the head of the Swan. You have reached the most beautiful double star in the sky. At 385 light-years from us, Alberio consists of a yellow and blue star with this contrast noticeable in any telescope. In my many years of teaching at campgrounds, people come away with a slight variation of colour. But either way, you look at it, Alberio is a must-see object this summer.

Nudge your telescope about four degrees North West to a small globular cluster. Estimated to be 13.7 billion years old, M56 is located in Lyra and is home to a dozen variable stars. At close to 33,000 light-years distance from us, this magnitude 8.8 cluster is thought to contain more than 220,000 stars. It’s an oldie but a goodie. Keep moving north to the rectangle of four stars - the Harp. Almost centred between the bottom pair of suns named Sheliak and Gamma is the smouldering remains of a dead star. Catalogued as M57, the Ring Nebula is a fine example of a planetary nebula. The faint ring you see is the outer shell of gas from the deceased star. The central star is faint at magnitude 14. Before you leave the area located the faint galaxy known as IC1296 only four arc minutes away. This remote object is estimated to be 220 million light-years away or 100,000 times farther than the Ring Nebula.

Up by Lyra is a nice double star that is easily split in binoculars into the magnitudes 4.9 and 5.1 components. Now,">Double-Double, not the Tim Horton’s coffee.

Comet C/2014 E2 (Jacques) is slightly under naked eye visibility at the beginning of August and is moving across the night sky at a good clip. Throughout the month follow Jacques as the comet moving out of Auriga then up through Perseus, Camelopardalis, Cassiopeia and finally ending up in Cepheus by month’s end. Comet Jacques was discovered in March of this year and is the brightest in the sky this month. Try looking for it now before moonlight interferes in a week or so.

Considered one of the best and most popular meteor showers will peak on the night of Aug 12/13. Although the annual Perseids estimates are 120 meteors per hour, the moon will be three days past full and will for sure reduce the expected numbers. That is not to say - forget about it. Go out and enjoy the warm August nights and observe the shower and drink in as much starlight as you can. You never know what you will see.

The planet Jupiter has now swung to the morning sky and is slowly emerging from the solar glare. Venus is racing eastward meaning the two brightest planets of our solar system will converge on the morning of Aug 18. These worlds will be separated by about 20 arc minutes or two-thirds the size of the full moon. This pair will also hang below the Beehive cluster M44 but given the sky will be getting lighter with the dawn; you might not be able to image it as well. But if the sky is still dark enough, this would make a fantastic digital moment. Another picturesque moment comes on the last night of the month in the constellation Libra when the 35% lit moon teams up between Saturn and Mars. Some thirteen degrees to the east of the moon will be the 9th magnitude asteroid Ceres and magnitude 7.7 Vesta a short distance to the east.

This month’s full moon is called the Sturgeon moon and will be the second of three super moons in a row for 2014. Last month’s super moon was on July 12 and next month will occur on Sept 9. This month’s super moon becomes full the same hour as perigee occurs or the closest distance to the Earth thus making this the largest of 2014. This will create some very high tides. Super moons appear to be some 13% larger and 30% brighter and an ordinary full moon. Try imaging the rising moon while the sky is somewhat light. Also, try to use trees or buildings in the shot. New Moon (lunation 1134) will occur on the morning of the 25th.

Until next month, clear skies everyone.

Gary Boyle

eNews date: 
Friday, August 1, 2014