This May, see the rare celestial event behind the 'blue moon' phrase
- In May, skywatchers will have the rare opportunity to witness a "blue moon," which refers to the second full moon occurring within the same month, with the next one not expected until December 31, 2028.
This May, skywatchers will get the rare chance to see something that happens only once in a blue moon. In fact, it's the very phenomenon that gave rise to the phrase "once in a blue moon."
The so-called blue moon is the name given to a full moon that appears for the second time in the space of one month.
This is very rare since there are 29.5 days to a full lunation - the time between two successive identical lunar phases such as from full moon to full moon.
Because May has 31 days, there will be a second full moon after the first one occurs at the start of the month.
The first of the two full moon phases occurs on May 1 at 5:23 pm GMT. On May 31, Earth's satellite will then again appear fully illuminated. The exact full moon phase will be reached at 8:45 am GMT.
Because the moon will also be at its farthest distance from Earth the following evening at 405,839 kilometres, the full moon will appear the smallest this year.
The somewhat misleading name of 'blue moon' has been used for centuries, and yet its origins are a mystery. What we do know is that neither the first nor second full moon shines in a blue light.
Scientifically speaking, once in a blue moon can be taken to mean once every few years - the next blue moon will be the full moon on December 31, 2028.
Race between Venus and Jupiter
After sunsets in May, viewers across Europe can watch out for Venus lighting up just above the north-western horizon, the brightest celestial body after the sun and the moon.
Shortly afterwards, the giant planet Jupiter can also be seen in the western sky a little higher and further east than Venus. It is significantly dimmer than Venus but still brighter than the stars.
Over the course of the month, the two planets come ever closer to each other. Venus wins the race and overtakes Jupiter on June 9 in the constellation Gemini.
Venus is expanding its role as the evening star. However, it is not a star, not a hot and bright ball of gas, but our inner neighbouring planet that reflects sunlight.
A nice sight in the sky will occur on May 18 around 9pm GMT, when the thin crescent of the waxing moon passes by Venus. Two days later, the moon passes by Jupiter, when the waxing crescent will have become noticeably thicker.
Jupiter is noticeably shortening its evening visibility. At the end of May, the giant planet sets shortly after midnight. Under good viewing conditions, Saturn will appear at the end of the month in the morning twilight just above the eastern horizon.
A few shooting stars
The Eta Aquariids are active throughout the month. These are fast shooting stars with entry speeds into Earth's atmosphere of around 234,000 kilometres per hour, with almost all of them burning up.
Their parent comet is Halley's Comet. Maximum visibility is expected around May 6.
In Europe, the radiant is fairly low in the sky, meaning stargazers will see only a few shooting stars. In countries further south, up to 20 meteors per hour are expected.
Turning to star patterns, the distinctive Spring Triangle is getting easier to make out. This is made up of the three bright stars Regulus in Leo, Arcturus in Boötes and Spica in Virgo.
The constellation Libra, by contrast, is not particularly conspicuous and has to be sought deliberately.
In the zodiac, Libra is followed by Scorpio, which is just about to rise. Its bright red main star Antares is currently crossing the horizon line.
In antiquity, the stars of Libra still indicated the claws of Scorpio. In the south-east, the rising figure of Ophiuchus with the serpent is lifting itself above the horizon.
The Plough (or Big Dipper to those in North America) stands high above our heads almost at the zenith. Virgo is also currently passing through the meridian.
Between Virgo and the Plough, in addition to the constellation Canes Venatici, Coma Berenices can also be found. This constellation is quite faint but consists of numerous stars. It looks particularly good if you search this area with a bright pair of binoculars.
It is important to avoid disruptive moonlight as well as terrestrial light sources.
