Why Observations of Mercury are so Difficult

Mercury is the smallest planet in earth’s solar system as well as being the closest to the sun, and as such it poses unique difficulties when it comes to viewing the planet. Due to its position inside of earth’s orbit, as well as the relatively short orbit of Mercury there are very few times when the planet can be seen. When it is visible it is only for a short time and the entire planet appears as only a crescent shaped object at various points throughout its cycle. Despite these difficulties in viewing Mercury in close detail, it is brighter than any star in the sky and can be seen with the naked eye on any clear night.

Planets are visible due to the light that they reflect from the sun, although Mercury is quite small and is also the closest planet to the sun and reflects a great deal of light. Due to this it appears quite bright in the nighttime sky but because of its short orbit and position it is difficult for astronomers to see. The best time to view a planet is actually when it is furthest from the sun and this position is called the aphelion, whereas its position closest to the sun is known as the perihelion. This is the optimal position because too much light obscures the object and makes it impossible to see details on its surface.

Due to its position as an inner planet Mercury is viewed in phases much as the moon is, it will appear as a crescent shape before reaching what is referred to as full Mercury before again being viewed as a crescent shaped object. This is due to the earth’s position when trying to view the inner planet and it is quite difficult to see with a telescope. The planet also has a relatively short orbit, consisting of only 88 days, which makes the interval during which it can be seen relatively short.

Due to the combination of factors that affect the visibility of Mercury it can only be seen for one hour and seven minutes out of any day. In order to see the planet a clear view of the western horizon is necessary and when viewing the extremely bright planet, planetary filters are crucial in filtering out the brightest points of light. The time of year is also important when viewing Mercury in close detail and it is often during the first part of the year that it is the most visible.