How to Spot Mercury in the Predawn Sky This December — A Guide for Northern Hemisphere Observers

How to Spot Mercury in the Predawn Sky This December

Mercury has long been nicknamed the "elusive planet" because, as an inferior planet orbiting closer to the Sun than Earth, it generally stays low in the sky and can be lost in twilight glare. However, during the first three weeks of December observers in the Northern Hemisphere have an unusually good chance to see this swift, rocky world in the predawn sky.

When and Where to Look

Set an alarm for about 5:30 a.m. local time and find a site with a clear, unobstructed view of the east–southeast horizon. Look roughly 40–110 minutes before sunrise for a bright, yellowish-orange point of light low above the horizon.

Why This December Is Special

• Recent orbital events: Mercury was at inferior conjunction on Nov. 20, passing roughly between Earth and the Sun, and moved rapidly into the morning sky.
• Rapid brightening: By Nov. 27 (Thanksgiving Day) Mercury had brightened to about magnitude +1.0 and rose roughly 75 minutes before sunrise. By Dec. 5 it brightened to near magnitude -0.3 in dark pre-twilight, and around Dec. 7 it reaches about magnitude -0.4.
• Favorable geometry: A combination of a steep ecliptic angle at autumn sunrise, Mercury's position north of the ecliptic after crossing its ascending node on Nov. 18, and its proximity to perihelion (Nov. 23) all help lift Mercury higher and make it brighter in morning skies for northern observers.

Notable Dates

• Nov. 20: Inferior conjunction with the Sun.
• Nov. 27: Mercury at about magnitude +1.0 and visible about an hour before sunrise; a thin crescent phase (~20% illuminated).
• Dec. 5: Mercury rises shortly before morning twilight and brightens to ~–0.3.
• Dec. 7: An unusually favorable greatest elongation (~21°) with Mercury near magnitude –0.4 and about 62% illuminated.
• Dec. 9: Mercury may reach ~–0.5 and remain easy to spot for several days.
• Dec. 19: Mercury passes about 5.5° upper-left of Antares; the star will appear much dimmer than Mercury—binoculars may help locate Antares.
• Around Christmas: Mercury will fade into bright twilight and become difficult to see with the unaided eye.

What You'll See

Like Venus, Mercury shows phases. It appeared as a slender crescent (~20% illuminated) on Nov. 27 and will increase to roughly 62% illuminated by Dec. 7 as its apparent disk grows. To the naked eye Mercury looks like a bright star, though it will show a disk and phase through binoculars or a small telescope. For planetary detail, a good motorized telescope such as the Celestron NexStar 8SE can provide a clearer view of the crescent shape.

Observation Tips and Safety

• Choose a site with a wide, low-eastern horizon free of buildings and trees.
• Look during the recommended time window (about 40–110 minutes before sunrise) — earlier in that window is darker and easier for spotting Mercury.
• Use binoculars if you have difficulty locating it; once found, switch to a telescope for phases and finer detail.
• Never point binoculars or a telescope toward the Sun. Be sure Mercury has risen well before you aim optical gear.

Quick Planet Facts

Mercury orbits the Sun every 88 Earth days and is the fastest planet in the solar system (roughly 30 miles per second on average). Its rotation period is about 58.7 Earth days, producing extreme surface temperature differences — roughly 790°F (420°C) in sunlight and about -270°F (-170°C) on the night side.

Historically Mercury had two names: Mercury (Latin Mercurius) when seen in the evening and Apollo when seen in the morning. Ancient observers such as Pythagoras recognized they were the same object.

Joe Rao, who contributes to Natural History and Sky & Telescope and serves as an instructor and guest lecturer at New York's Hayden Planetarium, authored the original report.