Epoch J2000 Equinox J2000
|Right ascension||19h 48m 10.3521s|
|Declination||70° 16′ 04.549″|
|Apparent magnitude (V)||3.9974|
|Spectral type||G8III+F5III |
|U−B color index||+0.48|
|B−V color index||+0.88 |
|Radial velocity (Rv)||+3.1 km/s|
|Proper motion (μ)||RA: +79.31 mas/yr
Dec.: 39.08 mas/yr
|Parallax (π)||22.04 ± 0.37 mas|
|Distance||148 ± 2 ly
(45.4 ± 0.8 pc)
|Absolute magnitude (MV)||0.71|
|Temperature||5,068  K|
|Metallicity||-0.31 Fe/H |
|Rotational velocity (v sin i)||1.2  km/s|
|Age||5.0×108  years|
Epsilon Draconis (ε Dra, ε Draconis) is a fourth-magnitude star in the constellation Draco. This star along with Delta Draconis (Altais), Pi Draconis and Rho Draconis forms an asterism known as Al Tāis, meaning "the Goat".
In Chinese astronomy, 天廚 (Tiān Chú), meaning the Celestial Kitchen, refers to an asterism consisting of Epsilon Draconis, Delta Draconis, Sigma Draconis, Rho Draconis, 64 Draconis and Pi Draconis. Consequently, Epsilon Draconis itself is known as 天廚三 (Tiān Chú sān, English: the Third Star of the Celestial Kitchen.) Most authors do not use a traditional name for this star, using the Bayer designation; however, in the literature it can be found the name Tyl.
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 circumpolar throughout all of Europe, China, most of India and as far south as the tip of the Baja peninsula in North America 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 common to most cities.
The best time for 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.
Epsilon Draconis is a yellow giant star with a spectral type of G8III. It has a radius that has been estimated at 10 solar radii and a mass of 2.7 solar masses. 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 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. 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.
Epsilon Draconis is resolvable as a double star in telescopes of 10 centimeters aperture or larger. The companion has an apparent brightness of 7.3 at an angular distance of 3.2 arcseconds. It is a giant of spectral class F5, orbiting the yellow giant at about 130 astronomical units.
- "SIMBAD query result: * eps Dra -- Variable Star". Centre de Données astronomiques de Strasbourg. Retrieved 2010-12-18.
- van Leeuwen, F (November 2007). "Hipparcos, the New Reduction". Astronomy and Astrophysics. Centre de Données astronomiques de Strasbourg. 474 (2): 653–664. arXiv: . Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Retrieved 2010-12-18.
- Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV data. SIMBAD. Bibcode:1986EgUBV........0M.
- Mallik, Sushma V.; Parthasarathy, M.; Pati, A. K. (October 2003). "Li abundances and velocities in F and G stars". VizieR. Centre de Données astronomiques de Strasbourg. Retrieved 2010-12-18.
- Mallik, Sushma V.; Parthasarathy, M.; Pati, A. K. (October 2003). "Lithium and rotation in F and G dwarfs and subgiants". Astronomy and Astrophysics. 409 (1): 251–261. Bibcode:2003A&A...409..251M. doi:10.1051/0004-6361:20031084. Retrieved 2010-12-18.
- Soubiran, C.; Bienaymé, O.; Mishenina, T. V.; Kovtyukh, V. V. (2008). "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants" (PDF). Astronomy and Astrophysics. 480 (1): 91–101. arXiv: . Bibcode:2008A&A...480...91S. doi:10.1051/0004-6361:20078788. Retrieved 2010-12-18.
- Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 209. ISBN 0-486-21079-0. Retrieved 2010-12-12.
- (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
- (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived August 19, 2010, at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.
- Kaler, Jim. "Epsilon Draconis". Retrieved 2016-11-24.
- Bakich, Michael (1995). The Cambridge Guide to the Constellations. Cambridge University Press. p. 202. ISBN 0521449219. Retrieved 2016-11-24.