Rasalhague — Double Star in Ophiuchus
HIP 86032; Alpha Ophiuchi; 55 Ophiuchi
About Rasalhague
Description
Rasalhague is a white giant of spectral type A5III at magnitude 2.08, the brightest star in Ophiuchus. Located about 47 light-years from Earth, it has a luminosity of roughly 25 times solar. It is a binary system with a faint companion. Rasalhague is one of the nearest A-type giant stars to the Sun.
Observing Tips
Rasalhague marks the head of Ophiuchus (the Serpent Bearer), forming the northern apex of the large, sprawling constellation. It sits between Hercules to the north and the rich Milky Way star fields of Scorpius to the south. Best observed June through September.
History
The name Rasalhague comes from the Arabic 'ra's al-hawwa,' meaning 'the head of the serpent collector.' Ophiuchus is the unofficial 13th zodiacal constellation, as the ecliptic passes through it between Scorpius and Sagittarius. The constellation represents Asclepius, the Greek god of medicine.
Fun Facts
Rasalhague is only 47 light-years away, making it one of the nearest giant stars to the Sun. The Sun passes through Ophiuchus from November 30 to December 18 each year, making Ophiuchus an unofficial zodiac sign — but astrologers traditionally ignore it.
Observe
1Physical Properties
2Position & Identifiers
3How easy to split?
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | V. hard | V. hard | V. hard |
| 150 mm Newton 150mm Newt. | V. hard+ | V. hard+ | V. hard+ |
| Celestron C8 (203 mm SCT) C8 203mm | V. hard+ | V. hard+ | V. hard+ |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
4Visibility
Set a location in User Settings to see visibility data.
5Multiple Star System
Separation over time
Apparent separation over time, computed from ORB6 orbital elements. Steep curves indicate fast-changing pairs — catch them while they're splittable.
Eyepiece View
A: 2.1 · B: 5.0 · Sep: 0.8″ · PA: 248° · N up, E right
Unresolved · Rayleigh: 2.3″ · Dawes: 1.9″ · Eff: 2.3″
Explore
7
Size Comparison
8
Compare Stars
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Spectral Classification
10
Hertzsprung-Russell Diagram
11
Stellar Lifecycle
12
Blackbody Spectrum
13
Stellar Absorption Spectrum
Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.
14
Stellar Fusion
Discover
15Stellar Notes
16
Light Travel Time Machine
17
Relativistic Travel
Nearby in the Sky
Other targets within a few degrees — pan your scope a little and keep exploring.
Visibility scores assume a 150 mm Newton at Bortle 4.
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