Lunar Eclipse: what do you need to know

Lunar Eclipse Key Takeaways

A lunar eclipse happens when the Earth passes between the Sun and the Moon, casting a shadow on the Moon. This can only occur during a full moon when the Sun, Earth, and Moon are closely aligned.

1. Unlike solar eclipses, lunar eclipses are safe to view without eye protection and can be seen from anywhere on the night side of Earth.
2. When the Moon is totally eclipsed, it often appears reddish due to the refraction of sunlight through Earth’s atmosphere. The atmosphere scatters shorter wavelengths, like blue, leaving longer wavelengths, like red, to be bent towards the Moon. The intensity of the red color depends on the amount of dust or clouds in Earth’s atmosphere.

There are different types of lunar eclipses:

• Penumbral lunar eclipse: A penumbral lunar eclipse happens when the Moon moves through Earth’s penumbra, the lighter outer section of its shadow.
• Partial lunar eclipse: occurs when a portion of the Moon moves into Earth’s umbra, the central and darkest region of its shadow.
• Total lunar eclipse: The entire Moon passes through the Earth’s umbra.

The timing of a lunar eclipse is marked by “contacts,” which are specific moments when the Moon enters or exits different parts of Earth’s shadow.

Lunar eclipses can cause a rapid drop in temperature on the lunar surface, potentially leading to a “thermal shock” that may cause lunar rocks to crumble and gas to escape from within the moon.

Studying lunar eclipses has helped scientists understand the Earth is spherical and measure the Earth-Moon distance.

Lunar Eclipses in a history

The full moon shines. “Why is it unusually bright tonight?” you think, glance up, and see: along the left edge of its silvery disk, as if someone had brushed it with red paint. The lunar eclipse has begun.

Within an hour, something round and red, like a large disk of tinted glass, gradually covers the night luminary until it is completely hidden in this redness. And for a long time, the Moon will remain in this form, then the red circle will begin to slide off its right edge.

A lunar eclipse evokes different feelings. You can admire the copper-red disk of the Moon, the bluish rim at the edge of the shadow, rejoicing at how bright and luminous this eclipse has turned out to be. In ancient times, a dark crimson, blood-red lunar “eclipse” was terrifying. Not to mention those cases when the Moon, to the astonishment and anxiety of witnesses, completely disappeared from the sky! What if forever?!

The ancient inhabitants of South America, the Incas, believed that the Moon had turned red due to illness, and if it died, it might fall from the sky. Knowing that the Moon was a great friend of dogs, the Incas pulled dogs by their ears, crying out: “Mother Moon, Mother Moon!” The poor Moon, hearing the cries and pleas, gathered all its strength to overcome the illness and return to its former brightness.

The Normans, on the other hand, imagined that the red wolf, Mangarm, had finished off his family affairs and attacked the Moon. The brave warriors, of course, understood that they could not harm the celestial predator, but knowing that wolves could not stand noise, they shouted, whistled, and beat drums. The noise attack sometimes lasted two, or even three, hours without interruption.

Meanwhile, in Central Asia, the eclipse passed in complete silence. People watched indifferently as the evil spirit Rahu swallowed the Moon. No one made noise or waved their hands. After all, everyone knew that the good spirit Ochirvani had once cut the demon in half, and the Moon, passing through Rahu like through a sleeve, would shine again.

In Russia, it was always believed that an eclipse foretold disaster: “The moon perished and became like blood… and after a short time, light returned (and after two hours, it brightened again).” And the chronicler recalls how wise “old people” shook their heads and said: “Such a sign is not good!”

The Apparent Motion of the Sun, Moon, and Planets

The cause of lunar eclipses became somewhat clear to Eastern sages many thousands of years ago. But, like all important knowledge about the sky, it was a priestly secret. Greek scientists comprehended and uncovered the Chaldean and Egyptian wisdom.

Lunar eclipses always occur during the full moon when the Sun, Earth, and Moon align in a straight line. The Sunlit Earth casts a shadow into space. This shadow forms a cone extending a million kilometers into space; its cross-section is circular, and at a distance of 360,000 kilometers from Earth, its diameter is 2.5 times larger than the Moon’s. When the Moon fully enters this vast shadow, a total eclipse begins, sometimes lasting over an hour and a half until our satellite emerges into the light again.

Thus, the round and red shape is the space of Earth’s shadow that the Moon crosses. Aristotle clearly formulated this truth and made a very important conclusion: since the shadow cone always has a circular cross-section during every eclipse, it means that our Earth is round and can only be a sphere. This was the first (but not the only) proof of Earth’s sphericity.

What happens during a lunar eclipse?

If the plane of the Moon’s orbit coincided with the plane of Earth’s orbit (the plane of the ecliptic), then lunar eclipses would occur every full moon, regularly every 29.5 days. However, the Moon’s path is tilted 5° to the ecliptic plane, so it crosses the “eclipse circle” only twice a month at two “risky” points. These points are called the lunar orbit nodes.

Thus, for a lunar eclipse to occur, two independent conditions must be met:

1. It must be a full moon.
2. The Moon must be at or near a node of its orbit at that time.

Depending on how close the Moon is to the orbit node at the time of the eclipse, it may pass through the center of the shadow cone, making the eclipse last as long as possible, or it may pass along the edge of the shadow, resulting in a partial lunar eclipse. The Earth’s shadow cone is surrounded by a penumbra. In this region, only part of the Sun’s rays are blocked by Earth.

Therefore, there are also penumbral eclipses. These are noted in astronomical calendars, but they are invisible to the naked eye—only a camera or photometer can detect the Moon dimming during the penumbral phase. If the full moon occurs far from the lunar orbit nodes, the Moon passes above or below the shadow, and no eclipse happens.

Eastern priests, not yet fully understanding all of this, spent centuries meticulously recording lunar and partial eclipses. At first glance, the eclipse schedule seemed chaotic. Some years had three lunar eclipses, while others had none. Moreover, a lunar eclipse is visible only on the half of the Earth where the Moon is above the horizon at that moment. Thus, from any specific location, such as Egypt, one can observe only slightly more than half of all lunar eclipses.

However, persistent observers finally uncovered a great secret: over 6,585.3 days, exactly 28 lunar eclipses occur across the entire Earth. Over the next 18 years, 11 days, and 8 hours (which equals this number of days), all eclipses will repeat on the same schedule by simply adding 6,585.3 days to each occurrence. This “Saros” cycle, as the Greeks called it, allowed astronomers to predict eclipses 500 years into the future.

As the Moon’s orbital motion was studied more precisely, astronomers learned not only to determine the day of an eclipse (as was done using the Saros cycle) but also to calculate its exact start time.

Christopher Columbus was the first navigator to take an astronomical calendar on his voyages to determine the coordinates of discovered lands using lunar eclipse timings. His guide was the famous Regiomontanus tables, which predicted eclipses until 1506.

During his fourth voyage across the Atlantic in 1504, a lunar eclipse caught Columbus on the island of Jamaica. The tables indicated the eclipse would begin on February 29 at 1:30 AM Nuremberg time. Lunar eclipses start simultaneously everywhere on Earth. However, local time on Jamaica lags several hours behind German time because the Sun rises much later there than in Europe. The difference in time readings between Jamaica and Nuremberg exactly corresponds to the difference in longitude between these two places, measured in hours. At that time, there was no other method to determine the longitude of West Indian cities with any accuracy.

Columbus began preparing for astronomical observations on the shore, but the natives, already wary of the sailors, found their solar observations suspicious and refused to provide food supplies. So, Columbus waited a couple of days and then declared that he would deprive the islanders of moonlight that evening if they did not comply. Of course, when the eclipse began, the terrified Carib people were ready to do anything to make the foreigner restore the Moon.

The “miracle” began at 7 PM local “Jamaican” time, determined by Columbus’ solar observations.

A curious reader, upon reflection, will determine the longitude of the island as obtained by Columbus and, by consulting a map, will even find out how much the great admiral erred in measuring longitude.

A Blood Moon: What causes the red color during the lunar eclipse?

During an eclipse, the Moon hides in the Earth’s shadow and, it would seem, should completely disappear from view each time since the Earth is opaque. This would indeed happen if the Earth had no atmosphere. In reality, however, sunlight grazing the surface of the Earth passes through the atmosphere, scatters, and reaches the Earth’s shadow. Red and orange rays penetrate best through the thick air, and it is they that color the Moon’s disk crimson, brick-red, or copper, depending on the state of the Earth’s atmosphere.

A camera (preferably with a telephoto lens) loaded with color film will capture impressive images of the lunar eclipse as a keepsake. For the initial stage of the eclipse, shoot with an aperture of 8 and a shutter speed of 1/100 s for 65-speed film. When half of the Moon’s disk is in shadow, open the aperture to 4. During total eclipse, use an aperture of 4 and a shutter speed of 1–5 s, depending on the darkness of the Moon’s color.

Can lunar eclipses be seen from anywhere on Earth?

Lunar eclipses can be seen from anywhere on the night side of Earth, unlike solar eclipses which are only visible from specific locations. This means that more than half of the Earth can potentially view a given lunar eclipse.

The visibility of a lunar eclipse depends on two main factors:

1. Whether the Moon is above the horizon in your location.
2. Whether it’s nighttime in your area during the eclipse.

If both these conditions are met, you can observe the lunar eclipse. This wide visibility is because the Earth’s shadow on the Moon is much larger than the Moon’s shadow on Earth during a solar eclipse.

Lunar eclipses typically last between one to two hours, including both partial and total phases. This extended duration allows for a significant portion of the Earth to rotate into a position where the eclipse becomes visible, further increasing the number of potential observers.

It’s important to note that while lunar eclipses are visible from a large area, the exact appearance and timing of the eclipse will vary slightly depending on your specific location on Earth.

Materials we used to write this article:

1. Astronomy. Encyclopedia for children. 1997. ISBN 5-89501-008-3
2. https://en.wikipedia.org/wiki/Lunar_eclipse
3. https://sci.esa.int/web/observational-astronomy/-/38834-overview
4. https://www.space.com/30669-10-surprising-lunar-eclipse-facts.html
5. https://www.space.com/15689-lunar-eclipses.html
6. https://science.nasa.gov/moon/eclipses/
7. https://www.pbslearningmedia.org/resource/buac19-68-sci-ess-luneclipseexplain/lunar-eclipses-explained/
8. https://www.treehugger.com/things-you-didnt-know-about-lunar-eclipses-4863733
9. https://www.usi.edu/solarpalooza/educational-resources/science-of-the-eclipses