Sir William Lower (1570 – 12 April 1615) was an English astronomer from the early telescopic period, and a Member of Parliament.
He was born in Cornwall, and after studying at Exeter College, Oxford, he married and settled in South-west Wales. In 1607 he observed Halley's comet and took a number of careful measurements which he communicated to Thomas Harriot, by which it was determined that the comet was following a curved course. Lower suggested that the comet's orbit obeyed Kepler's laws (instead of being an atmospheric phenomenon or following a rectilinear path, as was generally thought at the time)
Using a telescope that had been provided by Harriot, Lower made a number of observations of the moon, and noted that its surface appeared irregular and "like a tart that my cooke made me last weeke". Similar observations were published by Galileo a few weeks later.
Lower married Penelope Perrot, the daughter of Sir Thomas Perrot and Dorothy Devereux, by whom he had three sons and a daughter. After Lower's death Penelope (née Perrot) married secondly Sir Robert Naunton, by whom she had a daughter Penelope, who married Philip Herbert, 5th Earl of Pembroke.
- Jones, Bryn. "Sir William Lower". Retrieved 13 August 2012.
- Alumni Oxoniensis 1500-1714 "Lower, (Sir) William, of Cornwall, gen. fil. EXETER COLL., matric. 10 June 1586, aged 16; of Treventy, co. Carmarthen, astronomer; student of Middle Temple 1589 (as son and heir of Thomas, of Winnow, Cornwall, esq.); knighted at Theobalds 11 May 1603; M.P. Bodmin 1601, Lostwithiel 1604-11; died 12 April 1615; brother of Alexander and Nicholas; father of Thomas 1643."
- Lower, Sir William (c.1570-1615), of St. Winnow, Cornwall and Trefenti (Tra'Venti), Llanfihangel Abercowin, Carmarthenshire, History of Parliament Retrieved 19 August 2013.
- Trefenty, Dyfed Archaeological Trust Retrieved 19 August 2013.
- Roche 2004.