The summer solstice occurs today, 21 June, at 11.38 UTC (GMT).

The summer and winter solstices mark the times when the Sun is at its furthest from the celestial equator (the projection of the Earth’s equator onto the sky). The world ‘solstice’ comes from the Latin solstitium meaning ‘Sun stands still’ because the apparent movement of the Sun’s path north or south stops before changing direction.

The summer solstice does not always fall on 21 June. Because the Earth takes approximately 365.25 days to go around the Sun, the precise time of the solstices and equinoxes occurs about 6 hours (0.25 days) later each
year, with a jump of a day backwards on leap years. The last time the summer solstice was not on 21 June was 1975 when it occurred on 22 June
at 00.27, and in the year 2012 it will occur on 20 June at 23.09.

Find out more about solstices and equinoxes in our fact file.

Hour Angle

To mark the solstice, the Royal Observatory is hosting Hour Angle by composer John Eacott, a free musical performance sonifying the exact moment of the summer
solstice. A real-time calculation of the Sun’s declination will be
transformed into live notation played by 12 musicians. The piece will
allow visitors the chance to experience the solstice in an
unforgettable way. The performance will start promptly at 12.08. Visitors are advised to
arrive early.

Karen Gillan (Doctor Who‘s Amy Pond) visits the Royal Observatory, Greenwich to learn about the Prime Meridian Line with space scientist Dr Maggie Aderin-Pocock, and the Great Bear with public astronomer Dr Marek Kukula.

Clip from Doctor Who Confidential, Series 5 Episode 11: Extra Time. First broadcast on BBC Three, 7:30pm Saturday 12 June 2010. Used by permission.

www.bbc.co.uk/doctorwho/s4/confidential/

Part public
lecture, part planetarium show, the Royal Observatory has joined forces
with research scientists in three of the most exciting fields of modern
space science to bring you a new experience in astronomy talks. With a
mixture of stunning telescope images and full-dome visuals our trio of
experts will show you the Universe and the science behind it as
you’ve never seen it before. All of our guest speakers are accomplished
science communicators and their talks are suitable for a general
audience.

Astrobiology: the new science of life in the Universe

Dr Lewis Dartnell (University College London)

Thurs 17 June, 19.00
Cost: £8/£6

Astrobiology is a brand new field of science, bringing together
biologists, astronomers and planetary scientists to investigate the
origins and limits of life on our planet and discover where life might
exist beyond the Earth. Join Dr Lewis Dartnell on a tour of the planets
and moons of our Solar System – and further afield to alien worlds
orbiting distant stars - to explore one of the greatest questions ever
asked: are we alone?

Violent birth: a Universe of star formation

Dr Mark Westmoquette (University College London)

Weds 14 June, 19.00
Cost: £8/£6

The birth of new generations of stars has shaped the evolution of
our Universe for billions of years. Starbursts are one of the most
extreme examples of this process: entire galaxies convulsed by a frenzy
of new star formation that can blast clouds of gas thousands of light
years into intergalactic space. Dr Mark Westmoquette guides us through
these violent cosmic neighbourhoods and explains how such colossal star
factories can help us to unravel the complex history of the Universe.

Our place in the Universe

Dr Rita Tojeiro (University of Portsmouth).

Thurs 19 August, 19.00
Cost: £8/£6

Over the last few decades astronomers have made enormous leaps in
charting the Universe around us. Now, with accurate positions for
millions of galaxies, we are finally able to trace the Cosmic Web in
which we live. But these cosmic maps do far more than simply catalogue
the contents of our Universe – they can help us to understand its
origin and evolution as well as its ultimate fate. Cosmologist Dr Rita
Tojeiro takes us on a voyage to the furthest reaches of space and
explains how astronomers are unlocking some of the fundamental secrets
of the Universe.