The definition of Draco Constellation
|Bright Stars (magnitude<3)||3|
|Brightest Star||Eltanin (γ Draco)|
|Adjoining constellations||Bootes, Hercules, Lyra, Cygnus, Cephei …|
|Fully visible region||+90° ~ −15°|
|Optimal observational duration||July|
Draco, a constellation that can be seen all year round in the northern night sky, lies north of Corona Borealis. Draco is one of the 88 modern constellations, and one of Ptolemy’s 48 constellations.
Draco is located in the north of Corona Borealis. It does look like a dragon winding in the Ursa Major, Ursa Minor and Hercules within a wild range. The soaring dragon head, which abutted Hercules, is made up of four stars, forming a quadrilateral, with the two brightest stars representing the dragon’s eyes. It has an area of 1083 square degrees, which ranks eighth in the whole sky. The brightest star in Draco is Etamin (γ Draco) with the apparent magnitude 2.23.
Draco is one of the circumpolar constellations (others are Ursa Major, Ursa Minor, Cassiopeia and Cephei). It can be seen in all seasons in the Northern Hemisphere, with latitude varying between +90° and −15°. The best month for observation is July. The center of Draco passes through the upper transit at midnight every May 24.
Discovering history of Draco Constellation
Draco is a constellation that can be seen all year round in the northern night sky. The head of Draco, which abutted Hercules, is made up of four stars, whose magnitude is 2, 3, 4 and 5 respectively, forming a quadrilateral. The dragon’s long body circled Polaris in half a circle. If you draw a straight line from the two stars of head to north, you will find the Polaris.
What is on the dragon’s tail is α Draco (magnitude: 4). It was famous in ancient Egypt though not bright enough. The reason is that α Draco was known as the “Polaris” 4000 years ago. According to ancient Egypt legend, there was a 100-meter-long tunnel under the pyramid of King Chiapus, and its direction was facing the α Draco. Ancient Egyptian priests always looked out at this “Polaris” from the tunnel.
The stars in Draco Constellation
As we all know, α Draco is the “Polaris” in ancient Egypt. Also, due to the precession, it will become the “Polaris” again around 21,000 AD. Though it is named α Draco, it is not the brightest star in Draco constellation. The visual magnitude of α Draco is 3.65, which is one degree lower than the brightest one Eltanin.
Draco has several notable binaries. For instance, Kuma (ν Draconis) contains two stars whose brightness are both 4.9. They are 62 arc seconds apart, so you can recognize them just with a telescope.
R Draconis and T Draconis
R Draconis and T Draconis both belong to the Mira variable stars. Mira variable stars are a class of pulsating variables characterized by redness, periods of more than 100 days, and luminosity variations of more than one magnitude. They belong to red giants and are at the end of a star’s evolution (the asymptotic giant branch). They are also at the stage of the planetary nebula that formed by the shell of gas that’s about to be thrown out and a degenerate White Dwarf remains.
The magnitude of R Draconis is between 6.7 and 13, and the period is 245.5 days. The magnitude of T Draconis is between 7.2 and 13.5, and the period is 421.2 days.
The brightest star of γ Draco has the magnitude of 2.2. The distance from Earth is 150 light years. It is a red giant star. γ Draco together with β Draco, ν Draco and ξ Draco forms the diamond part of the dragon head.
The magnitude is 6. μ Draco can be observed by the telescope with a diameter of 7.5 cm or more. The distance from Earth is 88 light years. The surrounding circle is 480 years.
ν Draco has a wide binary with the magnitude of 5. The two stars are both white and the brightness are the same. You can observe it by a binoculars or a small telescope. The distance from Earth is 100 light years.
Deep sky objects
A well-known nebula in the Draco is NGC 6543, which has a central bright star, but not easily observed. The nebula is also known as the Cat’s Eye Nebula because the bright star is surrounded by a bright blue-green shell of gas that looks like a cat’s eye.
The Cat’s Eye Nebula is a typical planetary nebula, located about 3,000 light-years from Earth. It is a beautiful view of a sun-like star in the final stages of its life. The dying star at the center of a planetary nebula erupts material over and over again, creating a beautiful pattern of shells.
There is also a well-known group of galaxies in the Draco, often referred to as NGC 5985 or Draconis group. From left to right are NGC 5985, elliptical galaxy NGC 5982 and NGC 5981, which are usually seen together in a telescopic field of view because they are only a little more than half the width of the full moon. The cluster is too small to count as a galaxy cluster, and they are not classified as a compact group. They lie about 100 million light years away from Earth.
After studying spiral galaxy NGC 5985 with spectrometers, astronomers found that its core radiated so strongly at certain wavelengths that it was classified as an seyfert galaxy (an active galaxy), too.
Not as well known as other tight groupings of galaxies, the contrast in visual appearance makes this triplet an attractive subject for astrophotographers.
Another spiral galaxy in the Draco constellation, nicknamed the “Tadpole Galaxy” (UGC 10214), is 420 million light-years away. Its striking tail is 280, 000 light-years long and is made up of many large, bright blue star clusters.
The Mythology of Draco Constellation
In ancient Greek legends, there was a great hero named Hercules. He completed 12 heroic feats of adventure in his life, such as subduing Nemea, the fierce lion, and so on.
The eleventh adventure was to retrieve three golden apples from an orchard guarded by a 100-headed dragon. Long ago, when King Zeus married Queen Hera, all the gods brought gifts to this couple. The goddess Gaia brought a tree bearing golden apples from the west coast of the ocean. The four daughters of The God of Night were told to watch over the orchard where the golden apple tree was planted. They were also assisted by a 100-headed dragon that never slept. Hercules was ordered to take the golden apples from the monster.
He found the great god Atlas, who was carrying the sky for atonement. Hercules promised him to carry the sky instead of Atlas, and let Atlas lure the dragon to sleep and kill it. Then he tricked the fairies and picked three golden apples to bring back. After getting the apples as planned, Atlas tasted the joy of freedom and did not want to turn his back on the sky any more, so he threw the apple at Hercules’s feet and prepared to leave. Hercules at once thought of a plan to free himself. “Let me,” he said, “tie a rope round my head, or the weight of sky will crush me.” Atlas thought this a reasonable request, and promised to carry it for him for a minute or two. As a result, Atlas was deceived and laid the burden of sky on his own shoulders again. Later Hera, lifted the dragon into the sky and became the Draco constellation.
There are three meteor showers in the Draco constellation, namely, the Draconid Meteor Shower, the Draconid α Meteor Shower and the Draconid October Meteor Shower, whose parent comet 21P/Giacobini-Zinner returns every 6.61 years. Where 21 is the serial number and P is a periodic comet. It is permanent and distinct from the name of any other comet, which was only discovered by astronomers in 1900. Its most recent perihelion passes were in June 1972, February 1979, September 1985, April 1992, November 1998 and July 2005.
According to the movement rule of the meteor cluster, whenever the parent comet passes perihelion date, its meteor shower peak; When the parent comet moves away from the sun, the meteor shower is rare. The last time comet 21P passed perihelion was in November 1998. On the evening of October 8, the same year, skywatchers in China and Japan simultaneously observed a massive meteor shower with up to 700 meteors per hour. Its radiant point is located in the Draco constellation, so is called Draconid Meteor Shower. The concrete radiating point is 262 degrees right ascension and 55 degrees declination.
The more familiar Leonid has a shooting speed of 71 kilometers per second, while the Draconid has a slow shooting speed of 20 kilometers per second. The Draconid Meteor Shower is more favorable at higher latitudes (north) than at lower latitudes (south). Leo and Perseid meteor showers are best observed in the early morning, while Draconids are best observed in the evening. Generally speaking, the sky from October 6 to 10 every year become the Draconids active performance stage. The best observation dates are October 8 and 9, and the best observation time is from 40 minutes after sunset to 12 p.m.