#AstroMiniBR: what are dark nebulae?

Every Saturday, the TecMundo and #AstroMiniBR bring together five relevant and fun astronomical curiosities produced by the collaborators of the non-Twitter profile to spread the knowledge of this science that is the oldest of all!

#1: The sky is black, it’s going to rain!

Of the many curious and intriguing things that the Cosmos harbors, nebulae dark ones are certainly among them. Do the following exercise for a few moments: you are an astronomer from the early 20th century, you are sitting at the end of an observatory telescope cataloging objects in the sky when suddenly you see an apparently empty region, starless and black as the darkest night. dark. What would that be? It took some time to discover that these objects are dark nebulae, interstellar clouds that contain a very high concentration of dust. This is because these objects scatter and absorb all incident optical light, making them completely opaque at visible light wavelengths. Dark nebulae are easier to detect when they are located in front of a bright emission nebula.

One of the most famous examples in the southern hemisphere is the nebula shown in the image above, the Coal Bag Nebula, in Cruzeiro do Sul. The average temperature inside this nebula is very low, ranging from -260 to -170 degrees centigrade. Because of these low temperatures and high densities, a dark nebula usually forms hydrogen molecules that allow the formation of new stars!

#2: Lunar and solar eclipses are common, but not so

Celestial phenomena like the lunar and solar eclipses are spectacular, no one can deny it. If they happened on a monthly basis, would they lose that charm by becoming something commonplace? By the way, on second thought, if the Moon orbits the Earth approximately every 28 days, why wouldn’t that be the period during which an eclipse occurs?

The truth is that these phenomena are not as simple and linear as they seem. A lunar eclipse occurs when the Moon enters the Earth’s shadow, whereas a solar eclipse occurs when the Moon’s shadow falls on the Earth. The reason they don’t happen every month is linked to the fact that the Earth’s orbit around the Sun is not in the same plane as the Moon’s orbit around the Earth.

The Sun, Earth and Moon are not really perfectly aligned. If the Solar System were a flat disk, like the old CD and DVD disks, this would be the plane of the ecliptic and all the planets are arranged on that disk. But the Moon would be located in another disk, inclined at an angle of 5.14 degrees in relation to this first one. So, following the moon’s orbit as it revolves around the Earth, it is sometimes above the plane of the ecliptic and sometimes below. For this reason, this play of shadow and light does not always make an eclipse possible!

#3: The moon smile

In the first few days of this week, the Moon put on a show of its own in the sky. And we’re not even talking about a full moon day! Those who had clear skies at night could contemplate a smile lit up among the stars, generated by the crescent phase of the Moon.

As we remember from our basic science classes, in our entire Solar System, the only object that has a luminosity of its own is the Sun. The perception of different lunar phases is due to the fact that sunlight illuminates the surface of the Moon in different ways (as the Earth does) as it orbits around our planet. This light is then reflected towards us and we get to see it in different brightnesses throughout the month!

#4: The birth of a distant Jupiter!

Last Monday (4), NASA reported that the Hubble telescope observed evidence of a planet forming similar to Jupiter in a process described as “intense and violent”. This Jupiter-like planet is forming in a protoplanetary disk of dust and gas orbiting a young star about 2 million years old.

It may seem like a lot, but on an astronomical scale this is a very short time and, in fact, this instant represents the birth of the star system. Our Sun, for example, is 4.6 billion years old and the planets formed around it also during its first million years!

#5: The Star of the Beginning of the Universe!

On March 30th, NASA announced the discovery of the most distant and oldest star in the Cosmos. The star, affectionately known as Earendel (“morning star” in Old English), was also celebrated by Middle-earth fans for being namesake of a character in JRR Tolkien’s mythology who was a great half-elf sailor who was responsible for carry a star across the skies.

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