The 40th parallel south is a circle of latitude that is 40 degrees south of the Earth's equatorial plane. It crosses the Atlantic Ocean, the Indian Ocean, Oceania, the Pacific Ocean and South America. Its long oceanic stretches are the northern domain of the Roaring Forties. On 21 June 2018, the sun is at 26.17° in the sky and at 73.83° on 21 December, in King Island, Tasmania, which is near the 40th parallel. The maximum altitude of the Sun is > 35.00º in April and > 28.00º in May. 40th parallel south also marks a line beyond which Andromeda constellation can no longer be observed.

Around the world

Starting at the Prime Meridian and heading eastwards, the parallel 40° south passes through: ! scope="col" width="125" | Coordinates ! scope="col" | Country, territory or ocean ! scope="col" | Notes ! scope="row" style="background:#b0e0e6;" | Atlantic Ocean ! scope="row" style="background:#b0e0e6;" | Indian Ocean ! scope="row" | 🇦🇺 ! scope="row" style="background:#b0e0e6;" | Indian Ocean ! scope="row" | 🇦🇺 ! scope="row" style="background:#b0e0e6;" | Pacific Ocean ! scope="row" | 🇳🇿 ! scope="row" style="background:#b0e0e6;" | Pacific Ocean ! scope="row" | ! scope="row" | 🇦🇷 ! scope="row" style="background:#b0e0e6;" | Atlantic Ocean