This weekend, Earth will be treated to a nice blue moon. Our planet’s only natural satellite won’t put on a pleasant azure hue (indeed, blue moons have nothing to do with color). Instead, it will be the second full moon for the month of May, following the full Flower Moon on May 1. The blue moon will reach peak illumination at 4:46 a.m. EDT on Sunday May 31. 

Seasonal vs. calendrical

According to the Farmer’s Almanac, there are two definitions of a blue moon—a seasonal blue moon and a calendrical blue moon.

A seasonal blue moon is one extra full moon within an astronomical season, or the dates between solstices and equinoxes. A typical astronomical season has three full moons within it. If it has four full moons instead, then the third may be called a blue moon. 

A calendrical (or monthly) blue moon is the one most of us are familiar with. It is the second full moon to fall in one calendar month—like in May 2026. It takes the moon roughly 29.5 days to complete one cycle of phases (new moon to new moon). So if a full moon falls on the first of the month on the calendar, there will be a second full moon at the end of the month. The only month in which a calendrical blue moon cannot fall is February. 

How rare are blue moons?

Blue moons are not quite as rare as the phrase “once in a blue moon” makes it sound. Calendrical blue moons happen every 2.5 years (or 30 months) on average, and seasonal blue moons fall about once every two to three years. 

The last calendrical blue moon was on August 31, 2023 and the next calendrical blue moon will rise just in time to ring in the new year on December 31, 2028. 

Two blue moons can also occur in one year. In 2018, January and March both had two full moons, with no full moon in February. The next time two blue moons will fall in one calendar year won’t be until 2037.

Why is it a micromoon?

May’s blue moon will also be a micromoon and the smallest micromoon of the year. Micromoons have nothing to do with size and everything to do with distance. Typically, the moon is about 238,855 miles away from Earth. Micromoons are further away, and this month’s micromoon will be 252,360 miles away. With the further distance, a micromoon may appear a bit smaller and dimmer than usual. 

On the opposite end of the spectrum are supermoons, which are closer to Earth at only 225,130 miles away.

How to watch and photograph a blue moon

If you want to see the blue moon rise over a historic city, the Virtual Telescope Project will broadcast the event live from Italy. 

NASA has also put together a handy lunar photography guide if you want to snap that perfect moon pic. If using a smartphone, NASA recommends stabilizing the device, turning off the flash, and tapping the moon on screen to focus the camera directly on it instead of the sky. Your brightness also needs to come down and taking pictures at twilight or as the moon clears the horizon will give the sensor less contrast. 

The post Look up for a blue moon on May 31 appeared first on Popular Science.

As NASA looks ahead towards Artemis III in mid-2027, the agency is sharing new details on several projects, including a future permanent moon base and a drone mission called MoonFall. The mission will send four drones to survey the surface of the moon’s South Pole to spot potential landing sites for future Artemis astronauts. 

According to the update, the Jet Propulsion Laboratory (JPL) in Southern California has been developing the drone design and testing prototype hardware ahead of the scheduled 2028 launch. Each drone will land on the moon’s surface and gather high-resolution imagery of the terrain over the course of a single lunar day (up to 14 Earth days). After each drone’s last flight, its survive-the-night payload will continue to work for several months. Payloads that are designed to survive-the-night can endure the sub-zero temperatures of the lunar night, which can get as cold as -208 degrees Fahrenheit.

Each of the four drones should weigh about 550 pounds, and stand at four-feet tall and seven feet in diameter. They will use a Lunar Dashcam imaging system to create maps of the terrain. The drones will also be equipped with a laser retroflector array so that mission control can precisely locate the drones, a neutron spectrometer system to help determine how much (if any) subsurface water is present, and a spectrometer to measure radiation.

Texas-based Firefly Aerospace was selected to build the spacecraft that will transport the drones. Firefly’s Elytra spacecraft will carry the drones for a 45-day transit from the Earth to the moon. After entering lunar orbit, it will deorbit and perform a braking maneuver to send out the drones roughly 31 miles above the lunar South Pole.  

No stranger to lunar exploration, Firefly Aerospace’s Blue Ghost lander became the first commercially built lander to reach the lunar surface in March 2025. While on the moon, Blue Ghost delivered 10 NASA instruments designed to gather lunar subsurface data and also snapped some beautiful images of a solar eclipse. 

Some scientists worry that extracting resources from the moon could jeopardize research, while many Indigenous nations see the moon as sacred and are against any desecration. 

As of now, NASA and 66 other nations have signed the Artemis Accords. While not an international treaty, the Artemis Accords is an agreement for high-level principles of space exploration and provides a basic legal framework for exploring and developing the lunar surface during this century. However, the NASA-led Artemis group is in direct competition with an initiative led by China to explore the lunar South Pole and potentially extract its resources. 

The post Four drones will go where no astronaut have landed—yet appeared first on Popular Science.

A new model explains how Ganymede got its molten core — which in turn has given Jupiter's largest moon its magnetic field.

The post How Jupiter’s Moon Ganymede Melted Its Core appeared first on Sky & Telescope.