A rare close-up of elusive Mercury captured by NASA. Photo: AP
THERE is little chance you will notice Alan Jones if he is standing next to Brad Pitt; the difference in magnitude is just too great. This is what happens when we try to spy Mercury. The smallest planet is almost always too near the sun to stand out.
Even so, two, maybe three times a year we might get a brief window of opportunity for a few days to see it in the eastern sky before sunrise - or as is the case now, in the western sky after sunset.
At a recent meeting of the Astronomical Society of Victoria attended by more than 100 astronomers, when I asked the question of how many had seen Mercury with their own eyes, fewer than half put their hands in the air. This underlines the difficulty of glimpsing the fleet-footed planet in our skies. Now is a good time to change all that.
Mercury races around our central star, completing one orbit in 88 days; hence it was given the name of the speedy messenger of the gods. Because it is only a third of Earth's distance from the sun, from our perspective it will never stray more than about 28 degrees from Sol in our skies. It also means we can never see this planet at midnight. The best chance to view it is when it is at its furthest east from the setting sun, or west of it at sunrise. Currently, it trails the sun across the sky and, when the sun sets, Mercury still has some way to go before it, too, disappears below the horizon. And there is your chance to nab it.
Typically, you will have about 90 minutes to observe it once the sun has set.
For the next week, Mercury will be as bright as the brightest stars, being one of the first to shine after sunset. Begin looking for it about 8pm and some 15-20 degrees above the western horizon. It will shine with a steady white light, and there are no comparably bright stars in that area of sky to confuse you. The red super-giant star, Antares, will be another 10 degrees higher than Mercury, and Mars slightly higher still.