If you’ve never seen the smallest planet in our solar system with your own eyes, this weekend brings a great opportunity. On Friday, September 22nd, Mercury will reach its highest point in the sky all year and become half-illuminated.

Mercury, also known as the “Fast Planet” for its rapid 88-day rotation around the Sun, orbits so close to our star that it is almost always lost in sunlight. Technically, the planet is present in the daytime sky almost all year round, but it is impossible to see it. It can only be seen occasionally, at dusk closer to sunrise or sunset on Earth.

Here’s what happens next week at Mercury’s “greatest elongation,” which refers to the point in its orbit where Mercury appears farthest from the Sun as viewed from Earth. Its greatest eastward elongation is when it is visible over the western horizon just after sunset, while its greatest westward elongation is when it is visible over the eastern horizon just before sunrise. The planet will also appear half-illuminated, known as “duality,” similar to the Moon in its first or last quarter phase.

Mercury’s greatest westward elongation will occur on September 22, but it will be in a good position to watch the sunrise throughout the week, sitting 17 degrees above the eastern sky. According to this In-The-Sky.orgA few days after reaching its highest point in the sky, it will become brighter and easier to see, showing a phase of motion that appears to be more than half illuminated. Mercury will be brightest and easiest to see in the morning sky from September 16-30.

It will be best seen about 30 minutes before sunrise from September 22 through early next week. You will need a clear and unobstructed horizon. A pair of stargazing binoculars will also be useful for spotting Mercury, which usually has a yellow tint. The next largest eastward elongation of Mercury will be visible in the evening after sunset on December 4, 2023.