Three bright planets grace dawn skies

Early risers can enjoy the sight of three bright planets at the moment just as dawn begins to break. One – Jupiter – is impossible to miss, having risen many hours earlier. But Saturn and Mercury both rise late in the night and can only be seen in the morning twilight.

Mercury and Saturn
Saturn, to the upper right, and Mercury between the elongated clouds, pictured on January 15 from East Kent. Image credit: Paul Sutherland/Skymania

After the Moon and Venus, Jupiter is the brightest Solar System body in the night sky, shining at magnitude -2. At the moment it lies just under 4° to the north of Spica, the brightest star in the constellation of Virgo.

Even a small telescope will reveal gaseous Jupiter’s disk, and show that it is squashed at the poles due to its rapid spin. Astronomers call this shape an oblate spheroid. Patient observation will further show that the disk is crossed by a number of bands and belts of different hues. The effect is more subtle to the eye than you might guess from photos of the planet.

A small telescope – or even binoculars – will also reveal the four Galilean moons, Io Europa, Ganymede and Callisto, stretched out in a line to either side of the planet. Their arrangement changes quite rapidly as they orbit Jupiter, so will look different from hour to hour and night to night.

More about Jupiter

Planets from latitude of Sydney
The arrangement of planets Mercury and Saturn as seen from the latitude of Sydney around an hour before dawn, plotted using the planetarium program Stellarium. Image credit: Skymania

Next planet to rise, more than two hours before the Sun, is Saturn, shining at magnitude 0. Having passed on the far side of the Sun in December, Saturn is not now hard to find as twilight begins. If you look with a telescope, you will see a straw-coloured disk, as well as the famous ring system. The rings are wide open at the moment because Saturn’s northern hemisphere is tilted towards us. It makes for one of the most stunning sights in the sky.

Last of the bright planets to appear is Mercury, the innermost world in the Solar System, which, at magnitude 0, would be much more obvious if it could be seen in a darker sky. Another problem is that it remains low down before sunrise, so you need a clear horizon free of hills, trees and buildings in order to see it.

Mercury reaches greatest elongation west, when it is farthest in angular separation from the Sun, on January 19 after which it begins to draw back in towards the Sun. It is currently much easier to see from southerly locations than mid-northern latitudes due to the angle the path of the planets through the zodiac, known as the ecliptic, makes to the horizon.

From the latitude of Sydney, Australia, Mercury rises nearly two hours before the Sun and so gets to an altitude of 10° above the horizon before the sky comes too bright to see it. It will only reach half that altitude from cities at mid-northern latitudes such as Berlin, London or New York. Despite this challenge, the writer has been able to find, and photograph, Mercury over a sea horizon from the southern UK.

More about how to observe Mercury
Here is more about what to see in the night sky this month

Planets from latitude of London
The arrangement of planets Mercury and Saturn as seen from the latitude of London around an hour before dawn, plotted using the planetarium program Stellarium. Image credit: Skymania

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By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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