Mercury Shines in the Evening Twilight
21 May 2014

Fig (1)

This illustration shows the locations of the planets Mercury and Jupiter in the sky of Alexandria, on the evening of 25 May 2014.

Mercury, the smallest and innermost planet, is often difficult to observe with the unaided eye. As viewed from Earth, it is always close to the Sun in the sky, since its orbit lies within Earth’s orbit. Therefore, it is often immersed in the glare of the Sun. It appears only in the evening, after sunset, or in the morning, before sunrise. It never becomes visible nightly.

As Mercury circles the Sun, its elongation, or angular (apparent) distance from the Sun on the sky, varies, reaching a maximum of 18-28 degrees, twice every 116 days. At, and around the time of greatest elongation, Mercury is easy to observable with the naked eye, and becomes bright and relatively high above the horizon.

The next greatest elongation of Mercury will be on 25 May 2014. To observe Mercury at this elongation, look toward the western horizon, about 40 minutes after sunset. Mercury will be at west-northwest (halfway between west and northwest), and 12 degrees above the horizon. (Note: the apparent diameter of the Full Moon is 0.5 degrees.) Jupiter will also be easily identified, as it will shine as a brilliant white star, to the upper left of Mercury, at an altitude of 30 degrees.

Interestingly, as Mercury is closer to the Sun than Earth, it shows phases like those of the Moon. These phases can be tracked, through the telescope.

Your Sky

Aymen Mohamed Ibrahem
Senior Astronomy Specialist
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