Draco The Dragon

Ursa Major places a key role in helping identify other constellations such as Ursa Minor and namely the North Star. Located between these two iconic asterisms is Draco the Dragon. Its overall size measures 1,083 square degrees of sky and ranks eighth largest overall. No less than fourteen stars make up the Dragon’s asterism which begins with its head situated above the constellation Hercules.  

We presently refer to Polaris as the North or Pole Star. Such has not always the case. If we can go back in time to in 2787 BC, we would see Thuban (alpha Draconis) was the pole star at the time. This position slowly changes during the precession of Earth’s axis. Just as a spinning top slows down, its axis begins to wobble. Since Earth’s axis is tilted 23.5 degrees, the circle of precession also measures 23.5 degree wide and takes the 26,000 years to complete one revolution. In fact the star Vega will be somewhat the North Star 12,000 years from now. The same polar shift occurs in the southern hemisphere as well.

Thuban is a magnitude 3.6 giant star located 310 light years from us and appear to harbour an unseen companion that orbits every 51 days. Thuban is a white giant star of spectral class A0. Its surface temperature registers at 9800 Kelvin but shines a rare five times brighter than what it should be and 300 times more luminous than our Sun.

Now move eleven degrees to Edasich which is a K2 giant located 101 light years away. Edasich is one of the ten stars in Draco that have at least one orbiting extrasolar planet named Hypatia. Discovered in 2001, Iota Draconis b has the mass 8.9 times that of Jupiters and orbits once every 536 days.Half way between Iota and Theta Draconis is a fantastic group of elongated structures. They are NGC 5981, 5982, and 5985 with magnitudes of 12.9, 11.0 and 11.1 respectively. With distances estimated to be 170 million, 120 million and 180 million light years. Another fantastic edge-on galaxy is NGC 5907 also known as the Splinter or Knife Galaxy. It is only 56 million light years away and glows at magnitude 10.1. Measuring 11.3 arc minutes by 1.8 arc minutes, NGC 5907 is a must to hunt down and image.

The Cat’s Eye Nebula catalogued as NGC 6543 is a planetary nebula that lies 3,262 light years from us with a magnitude of 8.1. There is a strange structure to the remains of the central dead star. The theoretical cause is what was thought to be one central star is actually a binary star system. Some 10 arc minutes east of the Cat’s Eye is a real challenge. NGC 6552 is a magnitude 14.6 irregular spiral galaxy located an estimated 370 million ly away.

The Perseid meteor shower is active from July 17 to August 26 with best nights viewing at its peak on the 11/12 and again on the 12/13 and with no moon interference you should see more than 100 meteors per hour. The key is to find wide open spaces away from city lights, pack a lawn chair and enjoy. The particles strike the atmosphere at 60 km/sec and the Perseids also produce bright fireballs. 

Over the next weeks and months you should notice Mars begin to shrink in size and fade. The red planet was well publicized by the media during its closest approach since 2003 and peak the public’s interest to step outside at night and the lovely night sky. Mars is now up in the south east as the Sun sets. The planet Saturn is still in immersed in the Milky Way and forms a nice trio with the Lagoon and Trifid Nebulas.

The ringed planet sets just before 3 a.m. local time on the first of the month. In the lower western sky we see Jupiter that now sets at midnight. Venus has passed greatest angular distance from the Sun (elongation) and will begin to set lower and earlier as the nights tick by. This is my favourite time to follow Venus in a telescope. As Venus moves between the Earth and the Sun, its phase will change from half lit to crescent as well as grow in size.  

This month’s new Moon is slated for the 11th. Take advantage three nights before and after to enjoy the dark skies away from city light. The Milky Way is a sight only appreciated in person. The full Sturgeon Moon will occur on August 26.

Until next month, clear skies everyone.

Gary Boyle

Author: 
GARYBOYLE
eNews date: 
Wednesday, August 1, 2018
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