Skywatchers will have their best chance of the year to spot Mercury on June 16, when the planet reaches its greatest eastern elongation.

Mercury, the closest planet to the Sun, is often difficult to observe because it remains near the Sun in the sky and is frequently lost in its glare. While many people have seen bright planets such as Venus, Jupiter, Mars and Saturn, Mercury is one of the least observed planets with the naked eye.

An elongation occurs when Mercury reaches its greatest apparent distance from the Sun as seen from Earth. At greatest eastern elongation, the planet appears above the western horizon shortly after sunset, making evening observations possible.

"The days around this greatest eastern elongation offer the best opportunity of the year to observe Mercury, with nearly ideal viewing conditions," said Song Yuanyuan, a science outreach expert with the Tianjin Science and Technology Museum and a member of the Chinese Astronomical Society.

Mercury will remain relatively high above the horizon after sunset, allowing observers a longer viewing window, according to Song. Bright planets Venus and Jupiter can also serve as useful reference points for locating Mercury in the evening sky.

Earlier this month, Venus and Jupiter appeared close together in the western sky after sunset. During Mercury's elongation, Venus will move to the upper left of Jupiter, while Mercury will appear below and to the right of Jupiter.

Mercury is expected to shine at about magnitude 0.5, making it visible to the naked eye under favorable conditions. Observers with binoculars or small telescopes may enjoy a closer view, but astronomers advise waiting until after sunset before using optical equipment, as looking directly at the Sun can cause serious eye damage.

For the best viewing experience, observers should choose an open location with a clear view of the western horizon and begin observing about 30 minutes after sunset.