Ardra is the name of a nakshatra

Nakshatra

Nakshatra is the term for lunar mansion in Hindu astrology. A nakshatra is one of 27 sectors along the ecliptic...

 in Hindu astrology, the 4th or 6th depending on numbering scheme used.
The Sanskrit name ãrdrã translates to "the moist one".
It is associated with the star Betelgeuse

Betelgeuse

Betelgeuse, also known by its Bayer designation Alpha Orionis , is the eighth brightest star in the night sky and second brightest star in the constellation of Orion, outshining its neighbour Rigel only rarely...

 (α Ori).
The Ardra nakshatra extends from 06 degrees 40 minutes to 20 degrees 00 minutes of Mithun (Gemini).

The Hindu myth associated to Ardra is that of Taraka

Taraka

' was the second wife of Hindu God Brihaspati, God of planet Jupiter. According to the Puranas, Tara sired or mothered child named Budha through Chandra ....

. Taraka is an asura

Asura

-In Hinduism:In Hinduism, the Asuras constitute a group of power-seeking deities, sometimes considered sinful and materialistic. The Daityas and Danavas were combinedly known as Asuras. The Asura were opposed to the Devas. Both groups are children of Kasyapa...

who is granted invulnerability by Brahma.

The presiding deity is Rudra

Rudra

' is a Rigvedic God, associated with wind or storm, and the hunt. The name has been translated as "The Roarer", or "The Howler"....

, its symbol is a teardrop, the ruling planet is Rahu

Rahu

In Hindu mythology, Rahu is a cut-off head of an asura, that swallows the sun or the moon causing eclipses. He is depicted in art as a serpent with no body riding a chariot drawn by eight black horses. Rahu is one of the navagrahas in Vedic astrology...

.
In Tamil

Tamil language

Tamil is a Dravidian language spoken predominantly by Tamil people of the Indian subcontinent. It has official status in the Indian state of Tamil Nadu and in the Indian union territory of Pondicherry. Tamil is also an official language of Sri Lanka and Singapore...

 and Malayalam Ardra is referred to as Thiruvathirai and Thiruvathira respectively.