An aarti is a devotional ritual that uses fire as an offering. It's usually made in the form of a lit lamp, and in the case of the Ganges River, a small diya with a candle and flowers that's floated down the river. The offering is made to the Goddess Ganga, also affectionately referred to as Maa Ganga, goddess of the most holy river in India. The aarti takes place facing the river. The lamps are lit and circled around by the pandits (Hindu priests) in a clockwise manner, accompanied by changing or songs in praise of Mother Ganga. The idea is that the lamps acquire the power of the deity. After the ritual is complete, devotees will cup their hands over the flame and raise their palms to their forehead in order to get the Goddess's purification and blessing.
Aarti in Hindi आरती also spelled arathi, aarthi from the Sanskrit word "आरात्रिक" with the same meaning is a Hindu religious ritual of worship, a part of puja, in which light from wicks soaked in ghee (purified butter) or camphor is offered to one or more deities. Aartis also refer to the songs sung in praise of the deity, when lamps are being offered.
The aarti plate is generally made of metal, usually silver, bronze or copper. On it must repose a lamp made of kneaded flour, mud or metal, filled with oil or ghee. One or more cotton wicks (always an odd number) are put into the oil and then lighted, or camphor is burnt instead. The plate may also contain flowers, incense and akshata. In some temples, a plate is not used and the priest holds the ghee lamp in his hand when offering it to the Deities. The purpose of performing aarti is the waving of lighted wicks before the deities in a spirit of humility and gratitude, wherein faithful followers become immersed in God's divine form. It symbolises the five elements: 1) ether (akash), 2) wind (vayu), 3) fire (agni), 4) water (jal), and 5) earth (pruthvi). Communal Aarti is performed in the mandir; however, devotees also perform it in their homes.