Astronomy – Super Facts

Pulsars the Cosmic Lighthouses

Super fact 108 : A Pulsar is a rapidly rotating neutron star that emits beams of electromagnetic radiation from its magnetic poles. The radioactive beam from a pulsar that is located where the sun is located would heat earth’s surface to tens of thousands of degrees. The pulsar may rotate hundreds of times per second, and we only detect the beam when it crosses our line of sight. A neutron star, or a pulsar, is vastly denser than the Sun, typically hundreds of trillions of times denser.

As mentioned, a pulsar is a rapidly rotating neutron star that emits beams of radiation from its magnetic poles. A neutron star is an ultra-dense remnant left behind when a massive supergiant star runs out of fuel and collapses. You can read more about neutron stars in my post here and you can read about neutron stars that act like super magnets called magnetars here. This web page feature a calculation of what the intensity of a pulsar beam would be if it hit Earth and the pulsar is located where the sun is.

A blue pulsars / neutron star directs a beam toward earth and burns the surface. — The beam from a pulsar hits earth causing destruction. This is an AI picture generated by me and ChatGPT.

I consider this a super fact because pulsars are a very extreme type of star, which existence I believe comes as a surprise to many people.

Blue neutron star on black background with two bright blue beams. Compact supermassive object. | Pulsars the Cosmic Lighthouses — Pulsar with energetic jets in space. Shutterstock asset id: 2697475389 by Nazarii_Neshcherenskyi

Below is a one and a half minute NASA video explaining what a pulsar is. It is taken from this website.

Different Types of Neutron Stars and Different types of Pulsars

At top there is some text stating “A neutron star is a dense core left behind after a massive star goes supernova and explodes. Though only about 10 to 20 miles (15 to 30 kilometers) wide, they can have three times the mass of our Sun, making them some of the densest objects in the universe, second only to black holes. A teaspoon of neutron star material would weigh 4 billion tons on Earth. There are several types of neutron stars.” : Below the text at the top there is a picture of a magnetar, a pulsar and a magnetar plus pulsar. The text for each picture says: Magnetar - A magnetar is a neutron star with a particularly strong magnetic field, about 1,000 times stronger than a normal neutron star. That's about a trillion times stronger than a normal neutron star. That's about a trillion times stronger than Earth's magnetic field and about 100 million times stronger than the most powerful magnets ever made by humans. Scientists have only discovered about 30 magnetars so far. Pulsar - Most of the roughly 3,000 known neutron stars are pulsars, which emit twin beams of radiation from their magnetic poles. Those poles may not be precisely aligned with the neutron star's rotation axis, so as the neutron star spins, the beams sweep across the sky, like beams from a lighthouse. To observers on Earth, this can make it look as though the pulsar's light is pulsing on and off. Magnetar + Pulsar – there are about six known neutron stars that are both pulsars and magnetars. — Courtesy NASA/JPL-Caltech, Attribution, via Wikimedia Commons

Neutron stars are extreme stars. They are small super dense stars with extreme gravitational fields. They are in a sense like a gigantic atomic nucleus. Perhaps it is not surprising that they are extreme in other ways as well. There are pulsars, neutron stars which emit twin beams of radiation from their magnetic poles. Those poles may not be precisely aligned with the neutron star’s rotation axis, so as the neutron star spins, the beams sweep across the sky, like beams from a lighthouse. To observers on Earth, this can make it look as though the pulsar’s light is pulsing on and off.

There are different types of pulsars. Some spin extremely fast. They rotate hundreds of times per second, even 700 times per second. They are called Millisecond Pulsars. There are pulsars that emit beams of radio waves and pulsars that emit only gamma rays. A black widow pulsar a star system consisting of a rapidly spinning pulsar and a companion star that is being consumed by the pulsar like a black widow spider eats its mate. This link feature animation videos from NASA showing a star being consumed by a black widow pulsar.

Finally, there are magnetars, neutron stars with extremely powerful magnetic fields trillions and quadrillion times stronger than Earth’s magnetic field at the surface. You can read about them here.

Other extreme Celestial objects

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The Sun is White but the Sky steals its Blue

Superfact 105: The Sun is white, but the Sky steals its Blue is a poetic way of saying that the sun’s light is scattered by the atmosphere giving the Sun a yellowish tint as well as giving us our blue sky. From space the sun looks completely white.

Viewed from space the sun is entirely white. White light consists of a mix of all the colors of the rainbow. However, viewed from earth the sun has a yellow tint, which gets more pronounced, it even dips into orange, as the sun nears sunset. That does not happen in space as can be seen below in the one minute sunset timelapse video taken from the International Space Station.

Sunset Timelapse from the International Space Station

On earth the sunset looks more like something in the picture below.

The sun is setting over distant mountains. There are some clouds, a forest, and field in the foreground. The sun has a yellow tint; the clouds are slightly yellow-orange and sky above is blue. | The Sun is White but the Sky steals its Blue — The sky dusk has a dramatic background featuring a summer season golden sunset landscape. The light is at the horizon is an orange and yellow color with blue sky above. Shutterstock asset id: 2670235703 by Nature Peaceful

The sun is a so called yellow dwarf star, or a G-type main-sequence star. The term yellow dwarf is a bit of a misnomer, because they range in color from white, for more luminous G-types like the Sun, to only very slightly yellowish for less massive and less luminous G-type main-sequence stars. The sun emits all the colors of the rainbow simultaneously, but the most dominant color is green. However, this looks white to us.

When sunlight enters Earth’s atmosphere, tiny air molecules scatter shorter, blue wavelengths of light in all directions. This scattering is what makes the sky look blue. This is called Rayleigh scattering. Because much of the blue light is removed, the remaining wavelengths of light that reach your eyes combine to make the sun appear yellow. This is a super fact because it is a basic but surprising fact, and we know it is true.

Rayleigh Scattering

The blue color of the sky is caused by Rayleigh scattering of sunlight by the gases in the Earth’s atmosphere. The image below shows the degree to which Rayleigh scattering occurs at different wavelengths / frequencies of light. Blue has the shortest wavelength (highest frequency) for visible light and red the longest (lowest frequency). The curve shows that blue light scatters more than red light. It should be noted that UV light (not shown) scatter even more. The scattering curve shown is calculated for sunlight passing vertically through the atmosphere.

The graph shows the amount of scattering going from shorter wavelengths (higher frequences) on the left, to longer wavelengths (lower frequences) on the right. Blue has shorter wavelengths and red has longer wavelengths. The graph shows that blue scatter the most. — Figure showing the greater proportion of blue light scattered by the atmosphere relative to red light. Robert A. Rohde derivative work:KES47 (talk) (converted to SVG)., CC BY-SA 3.0 http://creativecommons.org/licenses/by-sa/3.0/, via Wikimedia Commons.

To see the Other Super Facts click here

The Moon has a Far Side but not a Dark Side

Super fact 103: The moon is always turning the same side towards us. This side is often referred to as the near side of the moon. The back side, which we can’t see from Earth, is often referred to as the far side of the moon. However, there is no side of the moon that is always dark. The near side of the moon and the far side of the moon both have day and night (in a 29.5 day cycle). Another interesting fact is that even though the near side and the far side of the moon get the same amount of light they are very different.

Below is a youTube video showing an animation composed of actual satellite photos by NASA. It shows the far side of the moon, illuminated by the sun, as it crosses between the DSCOVR spacecraft’s Earth Polychromatic Imaging Camera (EPIC) and telescope, and the Earth – one million miles away.

The video has frequently been shown on social media, and I’ve seen many comments stating that it is fake because the back side / far side of the moon is not dark in the video. However, the sun is behind us in the video and shining on both Earth and the far side of the moon. The far side is not always dark.

This is a super fact because many people mistakenly think there is a permanently dark side of the moon, which we know is incorrect and understanding the basics about the moon, the most prominent celestial object in the sky, aside from the sun, is kind of important.

Moon Photos

This is a close up photo of the near side of the moon. It is a full moon. Free picture from Pexels by Jay Brand.

A close up photo of the near side of the moon, but it is a crescent. — This is also a close up photo of the near side of the moon, but it is a crescent moon, which means that the far side, or the back side, is the side that is mostly lit up. In other words, the far side of the moon has day. Free picture from Pexels by Sevde.

I took the photo below with my phone a few minutes ago this evening. The little dot on the left (it is not twinkling) is the planet Venus. The moon is currently a crescent, which means that at the moment of my writing this the back side / far side of the moon has day. The sun is shining down on the far side, and it is reflecting light back into space. The back side / far side is almost a full moon right now, but we can’t see that from Earth.

It is a dark photo with a bright dot on the left and the moon crescent on the right. | The Moon has a Far Side but not a Dark Side — The dot on the left is Venus. On the right is the crescent moon. This photo is taken with my phone a few minutes ago (as of this posting).

Venus and the crescent moon are in the lower right corner and Jupiter in the upper left corner. — This is a zoomed out photo taken at the same time as the photo above. I zoomed out to capture a second dot up in the left corner. That’s another planet, the planet Jupiter (also not twinkling).

Interesting Moon Facts

I thought I might as well mention a few interesting facts about the moon.

On the left is the near side of the moon, and you can see the flat-lying basins called maria. On the right is the far side of the moon, and it does not have the maria. | The Moon has a Far Side but not a Dark Side — The Moon’s nearside and farside Image: NASA LRO / Jatan Mehta

The far side of the moon is different. As you can see in the YouTube video and photo above, the far side looks different from the nearside and it is different in appearance and terrain. The near side of the moon has large, dark, flat-lying basins called maria. They look like oceans. The far side is a lot more rugged and covered by lots of craters. Another difference is that the far side of the moon has a much thicker crust compared to the near side.

The sun is 400 times wider than the moon. They appear to be roughly be the same size in the sky because the moon is 400 times closer.

The moon is drifting away from earth at about 3.8 centimeters per year. The moon is moving away from earth due to the gravitational forces between the moon and earth, which also causes tidal bulges in the Earth’s oceans and the moon. Back in high school I took a difficult physics test for a competition and one of the questions was to show that the moon was moving away from earth due to gravitational forces and calculate by how much. I did not solve that one.

The moon was likely created by a celestial collision. The most widely accepted explanation for the existence of the moon is that the Moon was created when a planet-like object, the size of Mars slammed into Earth, soon after the solar system began forming. That was about 4.5 billion years ago.

NASA found water on the moon. In 2020, NASA announced the discovery of water on the surface of the Moon. The NASA video below features more interesting facts about the moon.

If you visit this link you’ll find an interactive 3D animation using the NASA Visualization Technology Applications and Development (VTAD) technology. By using your mouse, you can view the moon from many different angles and positions (both the near side and the far side of course).

To see the other Super Facts click here

Stars Twinkle but Planets Do Not

Super fact 102: Stars twinkle but planets do not. Planets reflect sunlight, like the moon, whereas stars emit intense light like the sun. However, stars are thousands of times further away.

The Sun and the Moon appear to have roughly the same sized disk in the sky, about 0.5 degrees of arc, because the Sun is roughly 400 times wider than the Moon but also about 400 times farther away. However, the moon, which reflects sunlight but does that emit any, is much fainter than the sun in our sky. The Sun provides approximately 400,000 times more light to Earth than the full Moon. If you were to move the sun farther away until it provided the same amount of light as the moon you would have to move the sun 632 times farther away until it became a tiny point in comparison to the moon.

The planets in our solar system, Venus, Jupiter, Mars, Mercury, Saturn, etc., appear in the sky as small discs reflecting light whereas the stars appear as intense points of light with a disc diameter that is thousands of times smaller than that of the planets. However, we can’t see the difference with the naked eye. Both planets and stars appear like points of lights to us, but the difference in disc size in the sky is very big.

The picture shows a big bright star (but much smaller than the sun) shining down on planet Earth lighting up the planet a bit. The light from the star is intense. | Stars Twinkle but Planets Do Not — Planets reflect light whereas the stars appear as intense points. Shutterstock asset id: 2709145593 by buradaki

Because stars are tiny intense points of light Earth’s atmosphere can easily refract (bend) their light. This is known as scintillation. I can add that the light from stars that are low in sky go through more atmosphere and therefore twinkle more. Since planets appear as tiny discs rather than tiny points, planets create a steadier beam of light, which averages out atmospheric turbulence. In addition, dust particles in space and in the atmosphere can more easily block the light from stars compared to that of planets, because the planets have much larger discs in the sky (thousands of times larger).

In the picture there is a disc representing a planet and a little yellow star and a small piece of space dust. The text says, “In a telescope the planet looks like a little disc whilst the star is still a bright point. However, to the naked eye both look like a star. Guess which one the space dust can make to twinkle by passing in front of it.” — To the naked eye a planet and a star point look light points of light. In a telescope the planet will turn into a disc, but the star will remain a bright point of light. For example, a piece of space dust can easily make the star twinkle by moving in front of it but won’t do that to the planet. Note: planets are much smaller than stars, but they are much closer and can look bigger.

Since this fact is not scientifically under question, a lot of people don’t know it, and it is kind of important to anyone interested in the night sky, I consider it a super fact. I should say that I borrowed this super fact from Jacqui Murray’s blog worddreams.

Planets Reflect Light like the Moon

Planets reflect light. They don’t shine and emit light like the sun or the stars.