Mercury CAN be seen from Earth.
More Info: Mercury can be seen from Earth with both the naked eye and the telescope. However, due to Mercury’s size and proximity to the sun it is difficult to spot with the naked eye. From your vantage point on Earth, Mercury appears very close to the Sun. In terms of degrees, the planet Mercury is appears between 17-28 degrees away from the sun (Powell, 2012). When observing Mercury through a telescope, you may have poor visibility due to its low altitude on the horizon. In addition, with a telescope you will see Mercury go through phases similar to our Moon’s (Rao, 2006).
When Can Mercury be seen from Earth?
According to NASA (2012), Mercury orbits the sun every 88 days. Due to this highly elliptic orbit, you can only see this planet either right before sunrise or right after sunset. You will not be able to see Mercury when the sky is completely dark. If you live in the Northern Hemisphere, the best time to view Mercury is on March through April evenings and September through October mornings. For the Southern Hemisphere the reverse is true. You can see Mercury roughly 45 minutes after sundown or 45 minutes before sunrise (Powell, 2012).
NASA.(2012). Mercury: Overview. Retrieved from http://solarsystem.nasa.gov/planets/profile.cfm?Object=Mercury
Powell, M. J. (2012). The Naked Eye Planets in the Night Sky. Retrieved from http://www.nakedeyeplanets.com/
Rao, J. (2006). Catch Mercury While You Can. Retrieved from http://www.space.com/2061-catch-mercury.html