What is the Light of the World? How to See the Miracle of the Moon in the Sky This Week
The moon has been in the headlines this month, after a successful lunar flyby during the Artemis II mission. And although the full moon usually takes center stage as the major lunar event of any month, unless there is a lunar eclipse, such as it was back in Marchthere are few times a year when the new moon is equally interesting, and one of those events is Earthshine.
Earthshine — something you might know from Rush’s song from the band’s 2002 album Vapor Trails — is the real deal in April, May and June. You know you’re looking at Earthshine when you look up at the moon, and you can see it all, but not like normal moonlight.
During a full moon, sunlight is reflected off the surface of the moon and sent to Earth, making it brighter and easier to see. In Earthshine, sunlight bounces from Earth to the moon, then back to Earth. This multiple reflection gives the moon a very dim, ghostly appearance.
It is visible only a few days a year, usually a few days before and after the new moon in spring. According to NASA, this is because the moon and Earth orbit in sequence in such a way that the light from the sun leaves the Earth, then the moon, and then returns to the Earth again. The song Rush sums it up perfectly when the band sings the phrase: “Some night, when the angles are right, and the moon is a tiny little piece.”
Michael Zevin, an astronomer at the Adler Planetarium, says this is due to the Earth’s higher albedo in the spring. Albedo is a measure of how much light comes from an area, with zero meaning no light and one meaning all light. Materials such as snow have a high albedo, while materials such as asphalt have a very low albedo.
“During the Northern hemisphere spring (between April and June), the Earth’s albedo is higher as there is still snow and ice in the Northern Hemisphere, which has a higher albedo than water or vegetation,” Zevin told CNET. Zevin also notes that spring is when the Northern Hemisphere is more inclined to the sun than winter, exposing much of that ice and snow to the sun and resulting in more light on the moon.
What is the best time to see Earthshine?
The actual dates change from year to year as the phases of the moon do not line up exactly from year to year. Earthquakes can occur any time there is a full moon in the spring.
This happens twice per lunar cycle, during the waning crescent and waxing crescent phases. Those phases occur just before and just after the new moon, respectively. The new moon is April 17, making the best days April 12-14 and April 19-22.
You don’t need special equipment to see it, but you do need time. Earthshine is only visible within about 45 minutes of sunrise and sunset, giving you about a 90-minute window twice a day to see it. Zevin says the best time to watch is early in the morning, just before sunrise. According to When the Curves Line Up, the effect should be strongest on April 14 and 22, so space photographers who want to get good shots should be ready on those days.
If you miss it in April, you’ll have four more times to watch it, including May 12-14, May 18-20, June 11-13, and June 17-19.
