Even though the planet Mercury is one of the brightest objects in the sky, it is one of the most rarely seen. But this week is one of the few occasions when the small planet is well-placed for skywatchers.
Although Mercury is always brighter than Saturn at its brightest, very few stargazers have ever seen it. As the innermost planet in the solar system, it never strays far from the sun, so is always seen against a bright background of twilight.
Twice each year, once in the evening and once in the morning, Mercury stands highest in the sky, giving skywatchers the best opportunity to spot it, weather permitting. This week is its best morning appearance of the whole year.
This sky map shows where to look to see Mercury.
Rise and shine Mercury
To try and see Mercury, skywatchers should go out any morning this week about a half hour before sunrise. You will need a low cloudless sky and unobstructed view of the eastern horizon.
Look just above where the sun will rise and you should spot tiny Mercury about 10 degrees above the horizon. A human fist held at arm's length covers about 10 degreesof the sky.
You may have to sweep with binoculars to see Mercury at first, but once spotted it should be visible to the unaided eye.
In a small telescope, you will see Mercury as a tiny half moon. It will probably look as if it's submersed in boiling water because of the turbulence of the Earth's atmosphere.
If you track Mercury with your telescope as it rises in the sky, the view should become steadier. Mercury will continue to be visible in your telescope after the sun rises, as it is bright enough to be visible through the blue sky, so long as you know exactly where it is.
Mercury: A strange planet
Mercury is one of the strangest worlds in the solar system.
It is the smallest planet, now that Pluto has been reclassified as a dwarf planet, at 3,032 miles (4,879 km) in diameter, only slightly larger than our moon. It has an odd, slow rotation period, 58.6 days, exactly two-thirds the time it takes to complete an orbit around the sun.
The surface of Mercury, as imaged by the two space probes that have visited it, looks very much like that of our moon, though with more craters and fewer open plains. It also experiences the greatest temperature extremes of any planet, ranging from 800 degrees Fahrenheit (426 degrees Celsius) to minus 280 degrees F (minus 173 degrees C) between day and night.
Legend has it that Johannes Kepler, who discovered the laws of planetary motion, never saw Mercury with his own eyes. This week is your chance to see the planet that Kepler missed—worth getting up early to see.