Here is a scintillating celestial spectacle that is visible to everyone on Earth this weekend – “planetshine”.
For anyone who starts observing the stars and watching the moon at home while locking, this is a sight to behold, and one you are sure to look for again.
April, May and June are the best months to see “planetshine” at its best, according to NASA.
The phenomenon of lightening on the dark side of the Moon only occurs in the last and the first days of the Earth’s orbit. Since there was a new moon on Wednesday this weekend, there will be three chances of seeing a magnificent crescent moon gradually grow.
By Friday it will be thin and low on the horizon at sunset. Saturday, a little higher and between two superb star clusters. Friday, the Moon will be brighter and much higher, close to the sparkling planet Venus.
On these three occasions, it will be possible, under clear skies, to see “planetshine”.
Here is everything you need to know about “planetshine” and how and when to see it this weekend.
What is the “dark side of the moon”?
There is no “dark side of the Moon”. The Moon is still 50% illuminated by the Sun, but because the Moon orbits the Earth every 29 days, we see its part of the wax illuminated towards full and decreases towards “New”, when it is lost in the reflections of the Sun.
This week, as the Moon emerges from this glare, its eastern member will always seem very slightly illuminated. However, the rest of the Moon’s surface, although obscured, will appear to be lit to our eyes. Why?
What is “planetshine”?
This is the earth albedo—Sreflected light from Earth and the Moon. It still happens, but it is only visible to the human eye when only a glide from the Moon itself is lit by the Sun. At the time, the Earth was the brightest view from the Moon – it was almost 100% lit by the Sun. So you have the perfect recipe for reflected light.
You can see “planetshine” by looking at left side of the Moon, its darkest part. You will be able to perceive some details there for a few nights until the brightness of the lit crescent waxes. As the nights go by, the Moon brightens and the Earth darkens), so your eyes will be submerged in light as albedo darkens – you will no longer be able to see “planetshine”.
Other names for “planetshine”
It’s also called “Earthshine” and “Earthlight”. On a crescent moon it is sometimes called “the old moon in the arms of the new moon” and on a waning crescent “the new moon in the arms of the old moon”.
The best times to see “planetshine” on the Moon
It is at its best on either side of a new moon in the spring of the northern hemisphere – April, May and June – when Arctic ice and snow reflect the most light (there is less mass terrestrial and less snow and ice in the southern hemisphere, so the effect is less in southern spring).
The phenomenon is easily visible for a few days before (therefore, very early in the morning) and after (after sunset) the New Moon. This last scenario applies this weekend, when “planetshine” will be detectable on Friday, Saturday and Sunday, and with some celestial views as a bonus:
Friday April 24, 2020:
With the Moon illuminated at 2%, it’s a great evening to see a thin crescent moon displaying “planetshine” at dusk near the western horizon. You may have to get up to see it, but it is visible (although it sinks quickly) for about an hour after sunset.
Saturday April 25:
A 6% illuminated Moon will be positioned between two splendid star clusters tonight in the constellation Taurus – the Hyades and the Pleiades (the latter is also called the “Seven Sisters”).
Sunday April 26, 2020:
With the Moon illuminated at 12% and the Earth reflecting less light, the “planetary glow” becomes more difficult to see, but you should still be able to distinguish it on the Moon because it seems to be close to Venus. The planet is now almost as bright as ever.
Are you going to see the light reflected by the Earth on the Moon? “Planetshine” will be back 12 nights after the “Super Flower Moon” on May 7 while our satellite “The new moon in the arms of the old moon” again.
I wish you a clear sky and big eyes.