WELCOME TO the June night sky. This is the month of the summer Solstice, when the Sun is at its highest point in the sky, staying above the horizon for the most hours. This, of course, gives us the longest day (15 hours) and the shortest night of the year.
If you were to travel north at this time, for example to London, the difference would be even more noticeable, with the Sun rising one hour earlier and setting one hour later, giving us 17 hours of daylight. If you were to continue to travel north, all the way to the Arctic Circle, in fact, the Sun would not set on this day and would skim the northern horizon giving 24 hours of daylight. This is the land of the “Midnight Sun”.
Now, when the Moon is full, it has to be 180 degrees away from the Sun and will rise at sunset. This also implies that when the Sun is high in the sky, the full Moon will be low and will rise in the southeast and set in the southwest for observers at our latitude in Portugal.
So, around midnight on June 11, the bright full Moon will loom low in the south between the constellations of Scorpios and Sagittarius. At this time, it may seen to be larger than normal, but this is just an optical illusion.
The Solstice date this year is on June 21 and the Sun will be 76 degrees above the horizon at midday. This is 15 degrees or 30 Sun diameters higher than in England at this time.
Visible all night in June is the planet Jupiter; still in the constellation of Libra, on the night of June 8, the Moon will be close. The planets Saturn and Mars cannot be seen well in June, as they both set in the west shortly after sunset.
The Moon is at First Quarter on June 3, Full on June 11, Last Quarter on June 18 and New on the June 25.
What is the
Summer Solstice?
The different seasons of the year are caused by a 23.5 degrees tilt of the Earth’s axis. Because the Earth is rotating and because of the gyroscopic effect, the axis of the Earth always points in a fixed direction; this is towards a point in space near Polaris, the Pole Star. The Earth is also revolving around the Sun. During six months of the year, the southern hemisphere is more exposed to the Sun than the northern hemisphere. During the rest of the year, the reverse is true.
• Clive Jackson is the director of the Astronomical Observatory of Tavira (Sitio do Malhão) and the Camera Obscura (next to the Castle in Tavira), specialising in education and public outreach. Tel 281 321 754, Fax 281 324 688, e-mail: [email protected] or visit http://www.cdepa.org
