Sunday evening will be marked by an unusual astronomical phenomenon, a total lunar eclipse. It will be visible immediately after sunrise. It is also called the Blood Moon because of the reddish hue that the Moon acquires during the eclipse. When the Moon enters the Earth's shadow (total eclipse) and sunlight passes through the Earth's atmosphere, it filters shorter wavelengths of light (blue and green) and lets through longer wavelengths (red), which are refracted and illuminate the Moon. Its hue resembles blood.

The full moon will rise on Sunday at 7:17 p.m. Central European Summer Time (CEST, data for Bratislava). The maximum phase of the eclipse will last from 8:11 p.m. to 8:56 p.m. CEST. At this time, the Moon will be only eight to 15 degrees high, meaning it will still be rising above the horizon. The phenomenon will end at 9:56 p.m.

According to weather forecasts, conditions for observing the eclipse should be favorable, with the clear sky only temporarily obscured by fog or low cloud cover in places.

"According to some information, many more people observe a lunar eclipse than a solar eclipse. While a solar eclipse is visible on a limited surface of the Earth, a lunar eclipse is visible wherever our cosmic neighbor is above the horizon, i.e. almost half of the Earth - provided that weather conditions allow it. When watching a lunar eclipse, we do not need a dark filter, there is no risk of eye damage like with a solar eclipse, if we neglect eye protection," photographer and publisher Marián Dujnič told TASR.

This is the first total lunar eclipse observable from Slovakia since the beginning of this decade. The phenomenon occurs when the Moon, Earth and Sun are on the same straight line. That is, the Moon in its orbit around the Earth passes through a place where our planet blocks the light coming from the Sun. The full Moon is always on the opposite side from the Sun. However, its orbit is inclined by 5.2 degrees to the Earth. Without this inclination, an eclipse would occur at every full moon, i.e. every 29.5 days.

When the Moon is completely in the Earth's shadow, a total eclipse occurs. If it only passes through part of the shadow, we speak of a partial eclipse, in which only part of the lunar disk darkens. Finally, if the Moon passes through only the penumbra, it is a penumbral eclipse, which is manifested by a slight darkening of the lunar disk.

As Marián Dujnič recalled, in the 1960s, Czech astronomer Jiří Bouška (1925–2014), associate professor of astronomy at Charles University in Prague, was a professional lunar eclipse observer. He collected time data on crater contacts with the Earth's shadow measured by friends of astronomy during lunar eclipses.

"As a 15-year-old, I measured several interactions of craters with the Earth's shadow in my hometown of Spišská Nová Ves during a partial lunar eclipse on June 14, 1965, and sent them to Associate Professor Boušek. He processed the observations and found that during this eclipse the Earth's shadow was two percent larger than calculated. I collaborated with Associate Professor Boušek in this area until the 1980s. Associate Professor Boušek published the results, including the names of the observers, in the Bulletin of the Czechoslovak Astronomical Institutes, published in English," said Marián Dujnič.

Even when the Moon is immersed in the Earth's shadow, it remains partially illuminated. This is caused by the scattering and refraction of light in the Earth's atmosphere. The faint glow of the Moon during a total eclipse is called the ashery.

In just a few years, three total lunar eclipses in a row will be visible in Slovakia - on December 31, 2028, June 26, 2029, and December 20, 2029.