Pleiades

Lore & Background

The Pleiades cluster contains the reflection nebulae NGC 1432, an HII region, and NGC 1435, known as the Merope Nebula. Around 2330 BC the Pleiades marked the vernal point. Due to the brightness of its stars, the Pleiades is viewable from most areas on Earth, even in locations with significant light pollution. The cluster is dominated by hot blue luminous stars that have formed within the last 100 million years. Reflection nebulae around the brightest stars were once thought to be leftover material from their formation, but are now considered likely to be an unrelated dust cloud in the interstellar medium through which the stars are currently passing. This dust cloud is estimated to be moving at a speed of approximately 18 km/s (11 mi/s) relative to the stars in the cluster. Computer simulations have shown that the Pleiades were probably formed from a compact configuration that once resembled the Orion Nebula. Astronomers estimate that the cluster will survive for approximately another 250 million years, after which the clustering will be lost due to gravitational interactions with the galactic neighborhood. Together with the open star cluster of the Hyades, the Pleiades form the Golden Gate of the Ecliptic. The Pleiades have been said to 'resemble a tiny dipper,' and should not be confused with the 'Little Dipper,' or Ursa Minor.

Reader's Guide

The Pleiades played an important role in ancient times for the establishment of many calendars thanks to its unique and easily identifiable appearance near the ecliptic and the fact that in the middle of the third millennium BC, this asterism marked the vernal point (2330 BC with ecliptic latitude about +3.5°). The cluster is displayed on the Nebra sky disc, found in Germany and dated to around 1600 BC, represented in a high position between the Sun and the Moon. In ancient India, it constitutes the first nakṣatra in the Atharvaveda (compiled around 1200-1000 BC), called Kṛttikā, meaning 'the Cuttings' or 'Those that mark the break of the year'. In Mesopotamia, the MUL.APIN compendium (dating from no later than 627 BC) presents a list of deities on 'the path of the Moon' beginning with mul.MUL. In Greece, the name Pleiádes is probably functional before having a mythological meaning, possibly from an Indo-European root expressing 'multiplicity, crowd, assembly'. The Ancient Arabs began their old parapegma calendar with M45 under the name al-Thurayyā. Although M45 is no longer at the vernal point, the asterism remains important functionally and symbolically, as seen in the ancient Yemeni Calendar of the Pleiades. The Pleiades are a prominent sight in winter in the Northern Hemisphere and are easily visible from mid-southern latitudes. They have been known since antiquity to cultures worldwide, including the Celts, pre-colonial Filipinos, Hawaiians, Māori, Indigenous Australians, Persians, Arabs, Chinese, Quechua, Japanese, Maya, Aztec, Sioux, Kiowa, and Cherokee. In Hinduism, they are known as Kṛttikā and associated with the war deity Kartikeya and the Saptamatrikas. Hindus celebrate the first day of the month of Kartika as Diwali. The Pleiades are mentioned three times in the Bible using the Hebrew name Kimah. The earliest known depiction is likely the Nebra sky disk (c. 1600 BC). Babylonian star catalogues name them MULMUL, meaning 'stars'. Some Greek astronomers considered them a distinct constellation, and they are mentioned by Hesiod, Homer, and the Geoponica. The Pleiades was the most well-known 'star' among pre-Islamic Arabs, often referred to simply as 'the Star' (an-Najm). Some scholars of Islam suggested they are the 'star' mentioned in Surah An-Najm. On numerous cylinder seals from the beginning of the first millennium BC, M45 is represented by seven points. As noted by scholar Stith Thompson, the constellation was 'nearly always imagined' as a group of seven sisters, and their myths explain why there are only six. Some scientists suggest these observations may come from as far back as 100,000 BC when Pleione was farther from Atlas and more visible as a separate star. In Japan, the cluster is mentioned as Mutsuraboshi ('six stars') in the eighth-century Kojiki, and is now known as Subaru, meaning 'to cluster together'.

Did You Know?

• The Pleiades is the Messier object nearest to Earth, at a distance of about 444 light-years.
• The cluster is displayed on the Nebra sky disc, dated to around 1600 BC.
• In Japan, the cluster is known as Subaru, from a verb meaning 'to cluster together'.