At its brightest, Mercury can be brighter than any star in the sky. Mercury shines by reflecting sunlight, like all the planets and the Moon. The albedo, fraction of sunlight a planet reflects, is 0.12 which is like weathered asphalt. Mercury doesn't wander far from the glare of the sun, on average only 0.387 AU, so it is hard for astronomers to see it clearly.

     Mercury is best seen at either the greatest eastern elongation or the greatest western elongation. At these points, which last for a few days at a time, Mercury can be seen near the sun at sunrise or sunset. At greatest eastern elongation, Mercury can be seen for a short time just above the western horizon just after sunset. At greatest western elongation, Mercury can be seen low in the eastern sky before the sun rises. The directions eastern or western only refers to where in the sky Mercury can be found relative to the sun. The points in Mercury’s orbit around the sun called the greatest elongation are also very close to the points where Mercury is closest, the perihelion, and the farthest, the aphelion.

The elliptical nature of Mercury’s orbit usually makes the angle between the Mercury and the horizon much less than 28°. (see pictures below) Observations of Mercury with the naked eye are best made at dawn or dusk. However very good telescopic views of Mercury can be made at midday when the planet is high in the sky. A yellow filter can easily filter out most the blue light from our sky. 

top...

Mercury travels around the sun every 88-days, so its synodic period, as seen from the earth is about 116 days or one-third of a year. You can see Mercury near the sun every 116 days either at dawn or dusk (see table). This also means that Mercury travels through the inferior conjunction at least 3 times a year. This is also called solar transit, although a solar transit requires that it directly between the sun and the earth, like in a solar eclipse. But because Mercury’s orbit is about 7° to the plane of the elliptic, it's not that common to find Mercury in solar transit. Usually when Mercury passes through the inferior conjunction it is either too far below or above the Earth (and our view).

This picture of Mercury (the black dot) in solar transit shown in a sun viewer was taken by the 150-ft. Solar tower at Mt. Wilson Observatory on Nov. 15, 1999.

Table with Elongations of Mercury for 1998-2004:

Mercury has phases like the Moon that can be seen with a telescope. It will go from crescents to gibbous to a full Mercury. They come from having only parts or all of Mercury's lit up side be visible to the Earth depending on the Earth point to view.

top...