How does a lunar eclipse occur?

A lunar eclipse occures when our celestial companion passes through the Earth's shadow. In a given year, a maximum of four lunar eclipses can occur, taking into account even the subtle penumbral eclipses. This limitation arises from the inclination of the Moon's orbit, which deviates approximately 5 degrees from the plane of the Earth's orbit. As a result, the Earth's shadow blankets a circular area with an angular diameter of merely 1.5 degrees at the Moon's distance. Consequently, lunar encounters with the Earth's shadow are infrequent, leading to the sporadic incidence of lunar eclipses. Consequently, the infrequency of the Moon's interactions with the Earth's shadow contributes to the rarity of total lunar eclipses.

When a full moon is positioned near the outer edge of the Earth's shadow, it results in a penumbral eclipse. If some imaginary astronauts had been standing on the far side of the Moon at that precise moment, they would have witnessed a remarkable sight - the Sun partially obscured by the shadowy Earth, surrounded by the captivating orange halo of our planet's atmosphere. A penumbral eclipse becomes visible when the Moon is in close alignment with Earth's shadow, creating the appearance of wisps of dark smoke on the edge of the full moon. In contrast, a partial eclipse presents a more dramatic spectacle. During this phase, a portion of the Moon in the sky is partially immersed in Earth's complete shadow. If the Moon is fully submerged, we witness a total eclipse. The total eclipse phase varies in duration, lasting from a few minutes to over half an hour. The entire eclipse event, including the penumbral phase, the partial phase, and potentially the total phase, until the Moon emerges from the shadow, unfolds over several hours. This extended timeline allows for the phenomenon to be observed not only across the entire Earth's hemisphere during nighttime but also when the Moon is rising at dawn or setting at dusk. On October 28, an eclipse will be visible across a vast expanse, encompassing the majority of the Eurasian continent, all of Africa, Western Australia, Greenland, Iceland, and partially, the eastern half of the American continent.

How will the eclipse unfold in the Czech Republic and Slovakia on 28th of October 2023?

VThe initial penumbral phase will be visible more than 3 and a half hours after moonrise, i.e. around 21:00 CEST. That's when we find a darkened full moon more than 35° high above the southeastern horizon in the constellation Aries from the lower left edge. The partial eclipse will begin at 21:35 CEST and last 1 hour 17 minutes. During this phase, the Moon will gradually move into Earth's shadow, with its southern edge obscured by more than 12% of its diameter, reaching the eclipse maximum at 22:14 CEST. The partial eclipse is expected to end just before 22:53 CEST. Following this, for approximately half an hour, the penumbral phase of the eclipse will be observable. During this time, the Moon will appear slightly dimmed, especially along its lower right edge. Throughout the entire duration of this celestial event, the bright planet Jupiter will be in relatively close proximity, situated approximately 6° east of the Moon. This conjunction sets the stage for a captivating celestial alignment, as the Moon and Jupiter will be in close proximity in the early hours of the following day. Moreover, gazing toward the south-southwest during the eclipse, the planet Saturn will also be an eye-catching feature, adding to the celestial spectacle.

The penumbral phase begins *     20 h 01 min 47 s CEST

The partial eclipse begins              21 h 35 min 18 s CEST

The maximum phase (12.2 %)       22 h 14 min 04 s CEST

The partial eclipse ends                  22 h 52 min 39 s CEST

The penumbral phase ends *          00 h 26 min 20 s CEST

* this phase is observable just before and just after the partial eclipse phase

How to observe this eclipse?

No special equipment is required to observe a lunar eclipse; it's visible to the naked eye. However, having a small telescope, such as binoculars, can enhance the experience by allowing closer examination of lunar craters. With this equipment, you may also notice that the portion of the Moon within Earth's shadow isn't entirely dark, as faint rays of sunlight refracted in Earth's atmosphere can illuminate this area.

Even if the sky is not entirely clear and there's a thin veil of clouds (as long as it's not completely overcast), lunar eclipses can still be observed. In fact, the presence of passing clouds can add intrigue to the experience. These clouds can scatter lunar radiation on the water droplets or ice crystals they contain, leading to captivating phenomena such as the formation of a lunar halo, an atmospheric corona, and more. During a partial lunar eclipse, the passage of thin clouds can therefore amplify the drama and add a captivating photogenic quality to the spectacle. To enhance the experience even further, the end of daylight saving time on that night means we get an extra hour of sleep on Sunday, making the observation even more enjoyable.

The next lunar eclipse visible from the Czech Republic will occur on Wednesday, September 18, 2024 in the early morning hours and will again be partial. We will see a total eclipse on Sunday, 7th of September, 2025.

Observing the eclipse in Opava

The Institute of Physics at Silesian University in Opava is welcoming the public to observe the upcoming lunar eclipse from the recently opened WHOO observatory on the 4th floor of the institute building located at Bezručova náměstí 13. This event requires registration and is scheduled to take place between 7 pm and midnight under clear sky. in addition to the lunar eclipse, there will also be an observation of the planets Jupiter and Saturn. More about the newly opened terrace in a separate article (will be uploaded soon).

Observing the eclipse at the observatory in Ondřejov

In the West dome of the observatory of the Astronomical Institute of the Academy of Sciences of the Czech Republic, there will be an observation for the public with an expert explanation from 9 to 11 p.m. Free, during clear sky only.

Contact information:

Mgr. Petr Horálek

RNDr. Tomáš Gráf, Ph.D.

Pavel Suchan

Press release of the Czech Astronomical Society and the Institute of Physics of the Silesian University in Opava No. 304 of 23rd October 2023.