3 Aquarii
A red giant irregular variable star in Aquarius.
3 Aquarii, also cataloged as k Aquarii and EN Aquarii, is a variable star located in the equatorial constellation Aquarius. With an average apparent visual magnitude of 4.429, it can be seen without optical aid under sufficiently dark skies. Parallax measurements place it roughly 590 light-years (180 parsecs) from Earth, with a margin of error of about 5%.
This star is classified as M3 III, indicating it is a red giant that has depleted the hydrogen in its core and moved away from the main sequence. Its angular diameter, corrected for limb darkening, is 5.60 ± 0.70 milliarcseconds. At its estimated distance, this corresponds to a physical radius approximately 108 times that of the Sun. The effective temperature of its outer atmosphere is about 3,450 K, which gives the star the cool, reddish appearance typical of M-type stars.
The brightness of 3 Aquarii fluctuates by up to 0.06 magnitudes, a variation first noted in the 1960s. It was formally recognized as a variable star in 1973 and assigned the designation EN Aquarii. Although classified as an irregular variable, more detailed analysis suggests the presence of multiple possible periods.
- Flamsteed designation
- 3 Aquarii
- Bayer designation
- k Aquarii
- Variable star designation
- EN Aquarii
- Mean apparent visual magnitude
- 4.429
- Annual parallax shift
- 5.57 milliarcseconds (5% margin of error)
- Distance
- ~590 light-years (180 parsecs)
- Stellar classification
- M3 III
- Angular diameter (corrected for limb dar
- 5.60±0.70 mas
- Physical radius
- ~108 times the Sun's radius
- Effective temperature
- 3,450 K
Lore & Background
3 Aquarii was first noted to vary in apparent magnitude in the 1960s, and it was formally listed as a variable star in 1973, receiving the designation EN Aquarii. Its stellar classification of M3 III indicates it is a red giant that has exhausted the hydrogen at its core and evolved away from the main sequence. The measured angular diameter, after correction for limb darkening, is 5.60±0.70 milliarcseconds, which at the estimated distance yields a physical size of about 108 times the radius of the Sun. The effective temperature of its outer atmosphere is 3,450 K, giving it the cool, reddish hue of an M-type star.
Reader's Guide
3 Aquarii is significant as a variable star that is visible to the naked eye in dark skies, with a mean apparent visual magnitude of 4.429. Its variability, first noted in the 1960s and formally recognized in 1973, amounts to up to 0.06 magnitudes. It is classified as an irregular variable, although detailed analysis shows multiple possible periods, preserving the uncertainty noted in the source. The star's physical parameters—distance of about 590 light-years, radius about 108 times that of the Sun, and effective temperature of 3,450 K—provide context for understanding red giant evolution. Its legacy lies in its multiple designations (Flamsteed, Bayer, and variable star) and its role as an example of an irregular variable star in a well-known constellation.
Did You Know?
- 3 Aquarii has a mean apparent visual magnitude of 4.429, making it visible to the naked eye in dark skies.
- The star's physical radius is about 108 times that of the Sun.
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