First published June 1, 2020.
On the evening of 5 June 2020, the full Moon of June, popularly called the Strawberry Moon, slid through the outer edge of Earth's shadow. Astronomers call this a penumbral lunar eclipse. It lasted a little over three hours, it was best seen from Europe, Africa, Asia and Australia, and at its deepest point the Moon looked only slightly greyer on one side. It did not turn pink or red. The name "Strawberry Moon" is an old seasonal label for June's full Moon, not a description of its colour.
Below is what actually happened that night, why a penumbral eclipse is so subtle, where the strawberry name comes from, and how to find the timing of the next eclipse in your own area.
The June 2020 eclipse at a glance
The eclipse reached its greatest point at 19:25 UTC on Friday 5 June 2020. From the first faint touch of the penumbra to the last, the event took about 198 minutes. Its penumbral magnitude was around 0.57, which means a little more than half of the Moon's diameter sat inside Earth's lighter outer shadow at mid-eclipse. None of it entered the dark inner shadow, the umbra.
Visibility depended on where the Moon was in the sky at that hour:
- Whole event visible: East Africa, eastern Europe, most of Asia and Australia.
- Moon rising during the eclipse: West Africa, much of western Europe and eastern South America, so observers there caught the later part low on the horizon.
- Moon setting during the eclipse: Northeast Asia and the western Pacific.
- Not visible: Most of North America, where the Moon had not yet risen.
For people in Europe the full Moon was climbing out of the evening twilight just as the shading was strongest, which is why many photos from that night show a large, warm-coloured Moon close to rooftops and hills.
What a penumbral eclipse really is
The Moon makes no light of its own. What we see is sunlight bouncing off its surface. When the Sun, Earth and Moon line up closely enough at full Moon, Earth blocks part of that sunlight and casts a shadow into space.
That shadow has two parts. The umbra is the central cone where Earth hides the entire disc of the Sun. Around it lies the penumbra, a much wider zone where Earth covers only part of the Sun. A Moon passing through the penumbra still receives most of its sunlight, so it dims only a little, and the effect is strongest on the side closest to the umbra.
Eclipses come in three main kinds:
- Total lunar eclipse: the whole Moon enters the umbra and usually glows coppery red, because the only light reaching it has been bent and filtered through Earth's atmosphere. This is the eclipse that earns the "blood moon" nickname.
- Partial lunar eclipse: part of the Moon enters the umbra, and a dark "bite" appears on its face.
- Penumbral lunar eclipse: the Moon only crosses the penumbra. The change is a soft greyish shading that many casual observers never notice, especially when less than the whole Moon is inside the penumbra, as in June 2020.
Some early reports in 2020 suggested the Moon would "give off" a strawberry or rose colour during this eclipse. That is not how it works. A reddish tint appears only in total (and sometimes deep partial) eclipses, and a low Moon can look orange or yellow on any night simply because its light passes through more of the atmosphere near the horizon. The penumbral shading itself is colourless. We explain the eclipse season around it in our guide to June 2020's solar and lunar eclipses.
Where the name "Strawberry Moon" comes from
Many cultures give each month's full Moon a name tied to the season. According to The Old Farmer's Almanac, "Strawberry Moon" was used by Algonquian peoples of the northeastern United States, and also by the Ojibwe, Dakota and Lakota, to mark the weeks when wild June-bearing strawberries ripen and are ready to gather. The Haida name "Berries Ripen Moon" carries the same idea.
The Almanac is explicit that the name has nothing to do with how the Moon looks. Older versions of this story claimed the Moon "took on a strawberry colour" and that this told people when to harvest. That reverses cause and effect: the berries gave the Moon its name, not the other way round.
Other names for the June full Moon include:
- Blooming Moon (Anishinaabe), for the flowering season.
- Green Corn Moon (Cherokee) and Hoer Moon (Western Abenaki), for tending young crops.
- Birth Moon (Tlingit), and Egg Laying Moon or Hatching Moon (Cree), for the season when many animals are born.
- Honey Moon and Mead Moon, names used in Europe.
These names are cultural and seasonal, so they describe every June full Moon, eclipse or not. The 2020 Strawberry Moon happened to coincide with a penumbral eclipse; most years it does not.
Four penumbral eclipses in one year
2020 was unusual because it contained four penumbral lunar eclipses and no total or partial ones. They fell on 10 January, 5 June, 5 July and 30 November. Some early articles listed the last one as "31 November", a date that does not exist; the correct date is 30 November.
Eclipses do not happen every full Moon because the Moon's orbit is tilted by about five degrees relative to Earth's orbit around the Sun. Most months the full Moon passes above or below Earth's shadow. Only when a full Moon happens near one of the two crossing points, called nodes, does it clip the shadow. Those windows come around roughly every six months, which is why eclipses cluster into "eclipse seasons" that often pair a solar eclipse with a lunar one about two weeks apart. In 2020, the 5 June penumbral eclipse came two weeks before the 21 June annular solar eclipse seen across Africa and Asia.
The June 2020 event belonged to Saros series 111, one of the long families of eclipses that repeat every 18 years and 11 days. It was one of the last members of that series, which is gradually drifting out of alignment.
Eclipses in older beliefs
Long before anyone could predict the geometry, a darkening Moon was a powerful sign. Many traditions explained eclipses as something attacking or swallowing the Sun or Moon. In Hindu mythology the demon Rahu chases and briefly devours them; in parts of South America, stories describe a jaguar or other creature attacking the Moon, and people made noise to drive it away. Elsewhere eclipses were read as a sign of divine anger or of quarrels in the sky.
Today we can calculate eclipses centuries ahead, which turns a once frightening event into a pleasant evening outdoors. Still, the old stories are a reminder of how closely people watched the sky, and how seasonal names like "Strawberry Moon" grew from a calendar based on the Moon and the land.
How to watch the next lunar eclipse
If you want to see a future eclipse for yourself, a little planning makes all the difference:
- Check local times. Eclipse times are usually given in UTC. Timeanddate.com lets you pick your city and shows when each stage happens and whether the Moon will be above your horizon.
- Know what to expect. For a penumbral eclipse, look for a gentle shading on one edge near mid-eclipse. For a partial or total eclipse, the change is dramatic and easy to see.
- No special equipment is needed. Unlike a solar eclipse, a lunar eclipse is completely safe to watch with the naked eye, binoculars or a telescope.
- Take comparison photos. Penumbral dimming is easier to spot in a sequence of photos taken with the same camera settings, an hour apart, than by eye.
- Find a low horizon. If the eclipse happens around moonrise, a clear view to the east helps, and a rising Moon near buildings or trees makes for striking pictures.
Whether or not an eclipse is happening, June's full Moon is worth a look. In the Northern Hemisphere it rides low across the sky around the summer solstice, so it often appears large and golden over the landscape for much of the night.
Sources: Wikipedia: June 2020 lunar eclipse; The Old Farmer's Almanac: Full Moon for June; Timeanddate.com: 5–6 June 2020 penumbral lunar eclipse; embedded photos from the Facebook page rabbitholeza.
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