Porrima — Double Star in Virgo
HIP 61941; Gamma Virginis; 29 Virginis
About Porrima
Description
Porrima, Gamma Virginis, is one of the most famous visual binaries in the sky — a pair of nearly identical F0 V dwarfs in a highly eccentric 169-year orbit. Both stars shine at magnitude 3.5, giving a combined magnitude of 2.7. The system lies just 33 light-years away, making it one of the closest bright visual binaries. Periastron passage in 2005 brought the pair to within 0.4 arcseconds — inseparable even in large amateur telescopes.
Observing Tips
In the 2020s the pair has widened to roughly 3-4 arcseconds — comfortable for a 4-inch telescope at 150x. The separation continues to grow, peaking around 2080 before closing again. Both components appear pale yellow-white and nearly equal, making Porrima one of the sky's finest "matched pairs." Find it by following the right-angle formed by Auva, Vindemiatrix, and Spica in southern Virgo. Best observed February through July.
History
Porrima takes its name from a Roman goddess of prophecy, preserved through medieval Latin astronomy. The binary nature was discovered by Bradley and Pound in 1718, and the orbit was first computed by Sir John Herschel in 1833 — making Porrima one of the first stars whose orbital motion proved that gravity operates beyond our solar system. The IAU formally adopted "Porrima" for Gamma Vir A in 2016.
Fun Facts
The periastron of 2005 was one of the most-observed binary events in amateur astronomy of that decade, with hundreds of separation measurements contributed by backyard observers worldwide. The two stars have similar masses (1.56 Suns each) and ages (~1.1 billion years), and they will both eventually evolve to giants roughly together. Sir William Herschel was one of the first to confirm that Porrima's components orbit each other, helping establish that binary stars exist beyond the solar neighborhood.
Observe
1Physical Properties
2Position & Identifiers
3How easy to split?
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | Medium+ | Medium+ | Medium+ |
| 150 mm Newton 150mm Newt. | Easy | Easy | Easy |
| Celestron C8 (203 mm SCT) C8 203mm | Easy | Easy | Easy |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
4Visibility
Set a location in User Settings to see visibility data.
5Multiple Star System Quadruple C,D,E,F: optical
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: 3.6 · B: 3.5 · Sep: 3.6″ · PA: 352° · N up, E right
Resolved · Rayleigh: 2.3″ · Dawes: 1.9″ · Eff: 2.3″
Explore
7
Size Comparison
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Compare Stars
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Spectral Classification
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Hertzsprung-Russell Diagram
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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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