This month offers sky gazers plenty of opportunities to observe the planets of our own solar system.

If the skies are clear on May 9 we shall see Mercury pass directly in front of the sun in an event called a solar transit. This event will last throughout most of the afternoon, starting from 1.12pm and continuing until sunset. Mercury is a small planet, just slightly larger than the size of Europe, from Portugal to the Caspian Sea (around 5,000 kilometres) so it will appear quite small when it crosses the face of the sun – which is 200 times larger in width.

To avoid damaging your eyes from the blinding radiation of the sun, project the sun’s image using a pair of binoculars onto a white card. Apart from its blindingly bright light, the sun also emits dangerous radiation in the infrared range so one should never look directly at the sun, not even with the naked eye.

Mercury and Venus are the only planets we can ever see crossing the face of the sun. This is because they are the only two planets whose orbits lie within that of the Earth. So only Mercury or Venus can be observed passing in front of the sun as seen from the Earth.

On May 9 we shall see Mercury pass directly in front of the sun

Back to the evening skies, the red planet Mars reaches opposition this month. This is when the Earth lies between the sun and Mars and when the latter is at its brightest as it will be closest to the Earth. Mars and the Earth (as all the other bodies in the solar system) orbit the sun in an elliptical orbit, not in a circular one. This delays the date of closest approach by a few days from the date of opposition. Current missions aimed to reach Mars include the European Space Agency’s ExoMars mission and Nasa’s InSight lander in 2018.

Saturn lies close to Mars, rising in the late evening as May begins. Its brightness will increase as it too approaches opposition later on in early June. Saturn, the ringed planet, forms a triangle with Mars and Antares. Antares is the brightest star in the constellation Scorpius, the celestial scorpion.

Jupiter is past its best, but still stands high in the sky soon after sunset throughout May. Its brightness will fade over the coming weeks, setting at around 3am when only a few months ago it was rising at just around that time. A pair of binoculars, held very steadily, will reveal the four Galilean moons. Even a small telescope will allow one to see the two largest equatorial bands in the giant planet’s atmosphere.

www.maltastro.org

Calendar of events during the month

May 4: Eta Aquarid meteor shower
6: Moon perigee: 357,800km
6: New moon
13: First quarter
15: Moon-Jupiter: 2.2° N
18: Moon apogee: 405,900km
21: Full moon
22: Mars opposition
22: Moon-Saturn
29: Last quarter

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