Ophiuchus is one of the 88 modern constellations and is located in the northern sky. It is one of the largest constellations in the sky, occupying an area of 948 square degrees. Ophiuchus contains several bright stars and deep sky objects that make it visible under moderately light-polluted skies.
Quick overview
Ophiuchus is best visible in the evening sky from May through July in the northern hemisphere. It is located near the celestial equator and hence can be seen from most locations on Earth except for the southernmost regions. The constellation lies northwest of the center of the Milky Way and hence has a very rich field of stars.
The brightest stars in Ophiuchus have apparent magnitudes between +2.0 and +3.0, making them clearly visible even from suburban locations. The constellation culminates around midnight during May-July, giving optimal visibility for several hours during the night.
Location and coordinates
Ophiuchus is located around the celestial equator spanning right ascension 16h 29m to 18h 24m and declination +12.7° to −26.9°. This places it northwest of the Milky Way center in the direction of the constellations Hercules, Serpens and Aquila.
In equatorial coordinates, the right ascension and declination coordinates can be used to locate Ophiuchus. The constellation extends across the following coordinates:
| Right ascension | 16h 29m to 18h 24m |
| Declination | +12.7° to -26.9° |
Ophiuchus passes through the zenith at latitudes between +48° and -30°. This makes it circumpolar (always above the horizon) from polar latitudes down to 30°N and up to 30°S. At mid-northern latitudes between 30°N and 60°N, Ophiuchus is visible during the evenings of late spring and early summer.
Description
Ophiuchus has a distinctive ‘kite’ shape formed by its brightest stars. It has several stars brighter than magnitude +3.0 spread across its area, with the brightest star Rasalhague shining at magnitude +2.08. Other bright stars in Ophiuchus include Cebalrai (+2.76 mag), Sabik (+2.43 mag), Sinistra (+2.75 mag) and Han (+2.80 mag).
The shape of Ophiuchus resembles a large man grasping a snake, the adjoining constellation Serpens. The main asterism consists of bright stars forming the kite shape along with a curved line of stars making the man’s legs. Stars marking the head of Serpens extend to the left of Ophiuchus.
Notable stars
Some of the notable stars in Ophiuchus are:
| Name | Magnitude |
| Rasalhague | 2.08 |
| Cebalrai | 2.76 |
| Sabik | 2.43 |
| Sinistra | 2.75 |
| Han | 2.80 |
Deep sky objects
Ophiuchus contains several famous deep sky objects visible in amateur telescopes:
| Object | Type |
| Barnard’s Star | Red dwarf star |
| IC 4665 | Open cluster |
| M9 | Globular cluster |
| M10 | Globular cluster |
| M12 | Globular cluster |
| M14 | Globular cluster |
| M19 | Globular cluster |
Best time to see
Due to its position straddling the celestial equator, Ophiuchus is best visible in the evenings during the month of June for observers at mid-northern latitudes. It appears in the southeastern sky after sunset and reaches its highest point in the sky around midnight.
The June-July timeframe offers the best combination of Ophiuchus being high above the horizon for maximum visibility of its stars and deep sky objects. The summer months also have more comfortable weather for nighttime stargazing.
Evening culmination
Ophiuchus culminates around midnight in early June. This means it will be highest in the southern sky and optimally positioned for viewing at that time.
The constellation’s altitude above the horizon provides the best view without any obstructions near the horizon. Ophiuchus reaches an altitude of almost +70° for observers at 40°N latitude, making its stars and deep sky objects appear clear and steady.
Length of visibility
Ophiuchus remains visible for several hours during its peak evening visibility period. In early June, it appears above the southeastern horizon around 8 p.m. local time. It remains observable well past midnight before setting in the southwest before dawn.
This gives skywatchers a large window of 4-6 hours during which Ophiuchus is high enough for excellent viewing on evenings with clear dark skies. Midnight is the sweet spot, with the constellation being highest in the sky.
Visibility based on location
Ophiuchus is best visible at latitudes between +30° and -30° as it transits near the zenith at these locations. It appears directly overhead at latitudes of +15°N like Hawaii and parts of Central America. From mid-northern latitudes, Ophiuchus appears high in the southern sky.
Northern latitudes
At latitudes between 30°N and 60°N such as most of the United States, Europe and northern Asia, Ophiuchus culminates 20° to 45° above the southern horizon. This altitude is sufficient for good views of the brightest stars and globular clusters.
Farther north above 60°N, Ophiuchus appears closer to the horizon with some southern parts setting below the horizon around midnight. The viewing period is shorter but the constellation is still observable at high northern latitudes.
Equatorial and tropical regions
People located near the equator between 15°N and 15°S latitude have the privilege of seeing Ophiuchus pass directly overhead. It is circumpolar above 15°S up to the Tropic of Capricorn at 23°S latitude.
From equatorial regions, Ophiuchus is visible for almost the entire night on its culmination dates in June. Excellent views are possible of the constellation’s extent from north to south spanning across the zenith.
Southern latitudes
From southern latitudes, Ophiuchus appears low in the northern sky and may be partially obscured. At 30°S, it culminates at an altitude of around 20° above the northern horizon which is adequate for seeing the main stars and asterisms.
Farther south in Australia, South Africa and southern South America below 30°S, the visibility decreases with the constellation skirting along the northern horizon. But its brightest stars can still be observed rising in the north during June evenings.
Factors affecting visibility
Like for all celestial objects, the visibility of Ophiuchus is affected by a variety of factors such as light pollution, cloud cover, moon phase and astronomical seeing conditions.
Light pollution
From large cities and suburbs, Ophiuchus may be challenging to observe due to washout from light pollution. Its stars are relatively faint, with most brighter than magnitude +3. Rural locations provide much better viewing opportunities.
Use tools like the Bortle scale to identify sites with darker skies where Ophiuchus will be more prominent overhead during June evenings. Seek out parks, nature reserves and campgrounds that are at least 50km away from large cities.
Weather conditions
Clear skies are critical for good visibility, so monitor weather forecasts a few days ahead of time to identify dates promising cloud-free conditions. Having several clear nights during early June will improve your chances of catching Ophiuchus at its peak.
Avoid overcast weather or hazy skies that will obscure the constellation. Fog, rain and snow will also negatively impact viewing conditions.
Moon phase and illumination
Avoid nights around the full moon phase as the increased illumination will wash out Ophiuchus’ fainter stars. Ideal conditions are provided on moonless nights or when the moon is just a thin crescent.
New moon dates in June provide the darkest sky conditions. The narrow crescent moon still allows reasonable darkness a few days after new moon while avoiding the extreme darkness before moonrise.
Seeing and transparency
Atmospheric turbulence can cause blurring and distortion of starlight, negatively impacting views of Ophiuchus. Look for nights advertised as having excellent or good ‘seeing’ forecast at local astronomy websites.
A stable atmosphere described as steady, undisturbed conditions will provide the sharpest views and resolve the constellation into fainter stars. Good transparency with minimal haze is also desirable.
Observing tips
Here are some tips to maximize your views of Ophiuchus:
- Use star charts to help identify the key stars and deep sky objects.
- Let your eyes adapt to darkness for 20-30 minutes.
- Use binoculars to sweep the area and zero in on objects of interest.
- Utilize telescopes and low power eyepieces to resolve globular clusters.
- Try observing from different sites to take advantage of clear skies.
- Photograph it with DSLR cameras using wide field and telephoto lenses.
Conclusion
Ophiuchus offers northern hemisphere skywatchers an excellent constellation to view during June evenings. Located near the celestial equator, it culminates in the southern sky around midnight for optimal visibility. The kite-shaped pattern containing several +2nd and +3rd magnitude stars is easy to identify under dark skies. Look for the bright star Rasalhague and sweep the area with binoculars to spot dazzling globular star clusters. Photographing Ophiuchus and its clusters provides a thrilling astrophotography challenge. With optimal planning for clear moonless skies in early summer, observers at most latitudes can take in the unique sights of Ophiuchus rising in the southeast after sunset.