Researchers have used advanced astronomical software to date a 2,500 year old poem accurately.

‘Midnight Poem,’ by lyric poet Sappho, who was a leading female pet of her time, describes night sky over Greece more than 250 decades ago. It depicts the Pleiades, a star cluster, having set at around midnight, when supposedly observed by her from the Greek island of Lesbos.

The software called Starry Night demonstrated that in 570 BC, the Pleiades set at midnight on January 25, which would be the earliest date that the poem could relate to. But as the years progressed, the Pleiades set progressively earlier.

Researchers also found that the last date the Pleiades would have been seen at the end of astronomical twilight (the moment when the Sun’s altitude is minus 18 degrees and the sky is regarded as completely dark) was March 31.

The study was published in the Journal of Astronomical History and Heritage.