National Astronomical Observatory of Japan

A Midsummer Night’s Dream


A Midsummer Night’s Dream

Uranus, the 7th planet from the Sun, is encircled by a ring and over 20 moons. The ring and 4 of the moons appear in this infrared picture taken by the Subaru Telescope. These moons take their names from characters in English literature. Oberon, visible in the lower left, is named for the king of the fairies in Shakespeare’s “A Midsummer Night’s Dream.” Midsummer, also known as the Summer Solstice, is the longest day of the year. Thus Midsummer Night is the shortest night of the year.

Earth’s rotation axis is tilted with respect to its orbit. So as the Earth travels around the Sun, the angle between the axis and the Sun changes. This causes the changing of the seasons and differences in the amount of daylight. On the Summer Solstice, Earth’s North Pole points closer to the Sun than at any other time of the year. This is what makes it the longest day.

The tilt of Earth’s axis is only 23.5 degrees. But Uranus’s axis is tilted by 97.8 degrees. This means that Uranus ‘rotates on its side’ as you can see in this picture. When Uranus experiences a Summer Solstice its pole points almost directly at the Sun. This means that seen from most of the planet, the Sun doesn’t set on the Summer Solstice. In other words, Uranus doesn’t have a ‘Midsummer Night.’

For Japan, the 2015 Summer Solstice occurs on June 22nd. Please take time to enjoy the starry sky on the shortest night of the year.

Text by: Ramsey Lundock (NAOJ)