Epsilon Draconis
Encyclopedia
Epsilon Draconis (ε Dra, ε Draconis) is a fourth-magnitude star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Draco
Draco (constellation)
Draco is a constellation in the far northern sky. Its name is Latin for dragon. Draco is circumpolar for many observers in the northern hemisphere...
. It has the traditional name Tyl. This star along with Delta Draconis
Delta Draconis
Delta Draconis is a yellow star in the constellation Draco. It has the traditional names Aldib, Altais and Nodus Secundus....
(Altais), Pi Draconis and Rho Draconis forms an asterism
Asterism
Asterism may refer to:* Asterism , a pattern of stars* Asterism , an optical phenomenon in gemstones* Asterism , a moderately rare typographical symbol denoting a break in passages...
known as Al Tāis, meaning "the Goat".
In Chinese astronomy
Chinese astronomy
Astronomy in China has a very long history, with historians considering that "they [the Chinese] were the most persistent and accurate observers of celestial phenomena anywhere in the world before the Arabs."...
, , meaning the Celestial Kitchen
Purple Forbidden enclosure
The Purple Forbidden enclosure is one of the San Yuan or Three enclosures. Stars and constellations of this group lie near the north celestial pole and visible all year from temperate latitudes in the Northern Hemisphere.-Asterisms:The asterisms are :...
, refers to an asterism consisting of Epsilon Draconis, Delta Draconis
Delta Draconis
Delta Draconis is a yellow star in the constellation Draco. It has the traditional names Aldib, Altais and Nodus Secundus....
, Sigma Draconis
Sigma Draconis
Sigma Draconis is a 4.7 magnitude star located at a distance of 18.8 light-years in the constellation Draco. Its traditional name is Alsafi.-Name:...
, Rho Draconis, 64 Draconis and Pi Draconis. Consequently, Epsilon Draconis itself is known as
Visibility
With a declination in excess of 70 degrees north, Epsilon Draconis is principally visible in the northern hemisphere, with southern locations north of 20° South able to see it just above the horizon. The star is circumpolarCircumpolar star
A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets , due to its proximity to one of the celestial poles...
throughout all of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, most of India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
and as far south as the tip of the Baja peninsula in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
as well as other locations around the globe having a latitude greater than ± 20° North. Since Epsilon Draconis has an apparent magnitude of almost 4.0, the star is easily observable to the naked eye as long as one's stargazing is not hampered by the light pollution
Light pollution
Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.The International Dark-Sky Association defines light pollution as:...
common to most cities.
The best time for your observation is in the evening sky during the summer months, when the "Dragon constellation" passes the meridian at midnight, but given its circumpolar nature in the northern hemisphere, it is visible to most of the world's inhabitants throughout the year.
Properties
Epsilon Draconis is a yellow giantGiant star
A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same surface temperature. Typically, giant stars have radii between 10 and 100 solar radii and luminosities between 10 and 1,000 times that of the Sun. Stars still more luminous than giants are...
star with a spectral type
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
of G8III. It has a radius that has been estimated at 10 solar radii and a mass of 2.7 solar masses
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
. Compared to most G class stars, Epsilon Draconis is a relatively young star with an estimated age of around 500 million years old. Like the majority of giant stars, Epsilon Draconis rotates slowly on its axis with a rotational velocity of 1.2 km/s, a speed which takes the star approximately 420 days to make one complete revolution.
In 2007, Floor van Leeuwen and his team calibrated the star's apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
at 3.9974 with an updated parallax of 22.04 ± 0.37 milliarcseconds, yielding a distance of 45.4 parsecs or approximately 148 light years from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. Given a surface temperature of 5,068 Kelvin, theoretical calculations would yield a total luminosity for the star of about 60 times the solar luminosity.
Star system
Epsilon Draconis is resolvable as a double starDouble star
In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary star, i.e...
in telescopes of 10 centimeters aperture or larger. The companion has an apparent brightness of 7.3 at an angular distance
Angular distance
In mathematics and all natural sciences , the angular distance between two point objects, as observed from a location different from either of these objects, is the size of the angle between the two directions originating from...
of 3.2 arcseconds. It is an orange dwarf star
Dwarf star
The term dwarf star refers to a variety of distinct classes of stars.* Dwarf star alone generally refers to any main sequence star, a star of luminosity class V.** Red dwarfs are low-mass main sequence stars....
of spectral class K5, orbiting the yellow giant at about 130 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s.
See also
- Lists of stars in the constellation Draco
- Class G Stars
- Variable starVariable starA star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
- Double starDouble starIn observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary star, i.e...
External links
- Astrophotographs:Epsilon Draconis
- SkyView Image: Epsilon Draconis