Tag: Sun

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Nature Science Stargazing Universe

The Belt of Venus or the Anti-twilight Arch

Full moon rising underneath the Belt of Venus
Full moon rising underneath the Belt of Venus

You now know why sunsets and sunrises are red (if not, read this article and find out!). But did you know that another beautiful light phenomenon occurs at sunset and sunrise, besides the beautiful reddish skies? It actually occurs opposite of where the Sun is setting or rising, thus opposite of where all the beautiful reddish colors light up the sky! So, next time you have a clear sky, try looking away from the nice sunset, in order to see the anti-twilight arch! But what is this anti-twilight arch?

Let’s explain its name first

The Belt of Venus, which is a stylized name for the anti-twilight arch, is a pink glow above the horizon, right opposite of where the Sun sets/rises. This opposite place of the Sun is actually an imaginary point, which we will call from now on the antisolar point (anti means opposite).

The phenomenon takes place during twilight – thus before sunrise or after sunset respectively. It is represented by a pink glow that surrounds, just like an arch, the horizon opposite of where sunsets and sunrises occur.

So there you have it – the anti-twilight arch!

Concerning the name “Belt of Venus”, contrary of what you might guess, it’s got absolutely nothing to do with the planet Venus, or any of its belts or rings (…which do not exist anyway!). Planet Venus has a smaller orbit around the Sun than Earth does, and this makes Venus visible to our eyes only around sunsets and sunrises, similar to how the antitwilight arch becomes visible at sunset and sunrise. This is the only association that the Belt of Venus might have with the actual planet. The name Belt of Venus is, in fact, inspired from the girdle which was supposedly worn by the goddess Venus and which might resemble the pinkish arch around the antisolar point, at twilight.

So what exactly is this Belt of Venus?

After sunset (or before sunrise), the Sun is below the horizon, relative to an observer on Earth. In the figure below, the observer’s line of sight is represented by the thin grey line and the Sun is below this line of sight, thus below the observer’s horizon. The dotted circle around Earth represents our planet’s atmosphere. Even though the Sun is below the horizon, right after sunset, light rays from the Sun still make way to get to the observer and even further (red arrow), till above the antisolar point, where they get backscattered off Earth’s atmosphere (pink arrow). This region, where the backscattering takes place, has a belt shape, and this belt is nothing else but the antitwilight arch!

In this figure, notice that the backscattering “point”, at the tip of the red arrow, is a little above the line of sight for the observer. The small region between the backscattering point and the line of sight, is represented by a dark belt, which is our planet’s shadow.

What will you, as observer, see? Well, if you look right opposite where the Sun is setting, you will notice, right after sunset, a faint pinkish light, stretching around the antisolar point, like a belt, or arch. As time passes, this pinkish glow will rise. Right underneath it, you will see a darker belt, which is nothing else than Earth’s shadow! As time passes further, the pinkish glow will rise even more, as will our planet’s shadow, until night will take over entirely and it will become pitch black outside.

This effect is sometimes very faint, and in order to get a good view, you will need, first of all, a clear sky. Best is also to have a clear horizon above the antisolar point as well, in order to distinguish this effect as better as possible.

So, now that you know about the antitwilight arch, I dare you to ignore a beautiful sunset and look right opposite! But I promise that if you do, you will get to see another magnificent optical phenomenon, less known, but of equal beauty! Have you already seen the Belt of Venus?

The Belt of Venus. Image credit: Kent Duryee (https://commons.wikimedia.org/wiki/File:Belt-of-venus.jpg), „Belt-of-venus“, https://creativecommons.org/licenses/by/4.0/legalcode
The Belt of Venus.
Image credit: Kent Duryee (https://commons.wikimedia.org/wiki/File:Belt-of-venus.jpg), „Belt-of-venus“, https://creativecommons.org/licenses/by/4.0/legalcode
Categories
Nature Science Universe

Why are sunsets and sunrises red?

Beautiful sunset over the Dammen Pond on the Vadsøya island
Beautiful sunset over the Dammen Pond on the Vadsøya island

This period in Vadsø, as in much of the Arctic region, nights begin getting longer and longer. It’s not yet the Polar Night, which means that everyday, beautiful sunsets and sunrises mark the beginning and the end of the dark, cold Arctic nights. But what makes sunsets so beautiful? Why does the sky and the Sun turn red?

In order to answer this, we need to review the same concepts we took into account when answering the question “why is the sky blue?“.

Light is an electromagnetic wave, just like radio waves, microwaves, and even the radiation resulted from radioactivity! The only difference between all these different electromagnetic waves is their wavelength.

Even the light that we actually perceive with our own eyes is made up of multiple wavelengths. And to each and all of these wavelengths of light corresponds a different colour! So, the light that comes to us from the Sun and which we see, is made up of multiple colours! Of all colours, to be exact!

Just like an ocean’s waves, light travels the same way: in waves! Blue light travels in shorter waves (with a shorter wavelength) and red light travels in longer waves (longer wavelengths).

When the sunlight, with all its colours, reaches Earth, it meets the planet’s atmosphere! Thus, it starts interacting with various particles in the air, such as tiny ice crystals, dust, water droplets and even gas molecules that make up the air itself! And once the light waves interact with these particles, it gets scattered!

For a wave to interact with a particle, the two must be of the same order of size. Smaller particles scatter short wavelength light (blue) stronger. Small air molecules, which make up the entire atmosphere, scatter the blue component of sunlight the most, and in all directions, because of its short wavelength! And this is why, during a sunny day, everywhere you look, the sky is blue!

At sunrise and sunsets however, the Sun, relative to us, finds itself at low positions in the sky. From these low positions in the sky, sunlight needs to travel longer distances, through thicker amounts of the atmosphere in order to reach our eyes.

At sunset and sunrise, sunlight travels a longer distance (pictured as the thick yellow arrow) through the atmosphere until it reaches our eyes.

Because of this, the light gets scattered more strongly by the atmosphere. Blue light, which gets scattered easiest, is in fact scattered so much, that it is mostly removed before it actually reaches our eyes. Which in turn means that there is more red light (which gets scattered the least) left for our eyes to see.

Me at sunset, on the shore of the beautiful Varanger fjord.
Categories
Nature Science Stargazing Universe

“Stargazing” during the day

Is a telescope useful during the daylight?
Is a telescope useful during the daylight?

The polar day has almost arrived in Vadsø and the night sky is almost as bright as during the daytime. Therefore, the stars, planets and other sky objects will not be visible anymore during “classical” stargazing sessions, under a dark night sky! But we at Aurora Labs, did find a possibility to enjoy the sky from an astronomical point of view nevertheless – even in daylight!

The International Space Station, or ISS as it is commonly known, is today the largest man-made object that flies in space, at around 400 km altitude above Earth. And because it has the size of a football field, it is big enough to be seen even from our planet!

The International Space Station orbiting Earth
The International Space Station orbiting Earth

Things are easier at night: if you look at the sky, the ISS will appear as a very bright star (approximately the same brightness as planet Venus). Because it is so bright, it should be seen even from urban areas! The bright dot suddenly appears on the horizon, moves steadily without changing speed or direction, and disappears again below the horizon. And it doesn’t blink as a plane does. If you’ve ever seen something like this, chances are that you’ve spotted the ISS! In addition, there are online tools and phone apps which calculate for you when ISS should be visible in your exact location – such as, for example, Spot the Station, provided by NASA.

You don’t need a telescope to see this show; however, to the naked eye, the ISS looks like a bright dot, with no other features. A telescope would permit you to see some features, as solar panels for example.

During the day, things are more difficult. At night, ISS is seen because it reflects the light of the already set Sun. During the day, however, a possibility to see ISS is when it passes across (or transits) the face of the Sun. And what a great sight that is! Be careful though, in order to see this great show, you need a properly equipped telescope with solar filters when you look at the Sun, otherwise the light of our star is so bright, that it can create even blindness!

Multiple photographers around the world have taken such photos of the ISS transiting the Sun or moon. ISS travels at a speed of around 28.000 km/h, so, can you imagine how precise you need to be in order to capture such a moment that only lasts less than half a second? Because – yes – the ISS transiting the Sun or moon lasts less than 0.5 seconds!

One of the most recent photos of this kind, is the one taken by the photographer Mack Murdoc from Los Angeles, which is a composite photo showing the ISS as it passed across the Sun.

"International Space Station Solar Transit." © Mack Murdoc - see the original publication on Mack Murdoc's Instagram: https://www.instagram.com/p/B_h851mHpah/
“International Space Station Solar Transit.” © Mack Murdoc – see the original publication on Mack Murdoc’s Instagram: https://www.instagram.com/p/B_h851mHpah/

During daytime hours, besides the ISS, it is possible to see even planets, such as Venus, transiting the Sun! In the photo below, the black dot is not a sunspot, as you might believe, but it’s no other than planet Venus!

Gestrgangleri (https://commons.wikimedia.org/wiki/File:20040608_Venus_Transit.JPG), „20040608 Venus Transit“, marked as public domain, more details on Wikimedia Commons: https://commons.wikimedia.org/wiki/Template:PD-self
Gestrgangleri (https://commons.wikimedia.org/wiki/File:20040608_Venus_Transit.JPG), „20040608 Venus Transit“, marked as public domain, more details on Wikimedia Commons: https://commons.wikimedia.org/wiki/Template:PD-self

And here, meet Mercury as the small black round dot (you can also see sunspots in this picture, and how different they look compared to the perfect round shape of a planet):

Elijah Mathews (https://commons.wikimedia.org/wiki/File:Transit_Of_Mercury,_May_9th,_2016.png), „Transit Of Mercury, May 9th, 2016“, https://creativecommons.org/licenses/by-sa/4.0/legalcode

The Moon is also sometimes visible in the sky during the daylight, and with a properly equipped telescope, you can see its features really well, too!

The Moon seen during the day
The Moon seen during the day

Last but not least, our Sun is a star, just like the million others out there that you can see in the night sky! Therefore it can be observed with a telescope as well! A specially equipped telescope with solar filters, of course, to protect your eyes from the extremely bright light! If you visit me here in Vadsø, I offer this activity as part of the Cloud Spotting under the Midnight Sun activity and we’ll have a look at our star and at its sunspots!

The Sun and a few sunspots
Categories
Nature Science Universe

Why is the sky blue?

Sunny blue sky
Sunny blue sky

Now that the polar day starts to make itself felt more and more in high latitudes, we’ll experience daylight round the clock here in Vadsø in less than 2 weeks! More daylight means more blue skies! But do you know why the sky is blue? Keep on reading to find out!

Light is an electromagnetic wave, just like radio waves, microwaves, and even the radiation resulted from radioactivity! The only difference between all these different electromagnetic waves is their wavelength.

Even the light that we actually perceive with our own eyes is made up of multiple wavelengths. And to each and all of these wavelengths of light corresponds a different colour! So, the light that comes to us from the Sun and which we see, is made up of multiple colours! Of all colours, to be exact!

Just like an ocean’s waves, light travels the same way: in waves! Blue light travels in shorter waves (with a shorter wavelength) and red light travels in longer waves (longer wavelengths).

When the sunlight, with all its colours, reaches Earth, it meets the planet’s atmosphere! Thus, it starts interacting with various particles in the air, such as tiny ice crystals, dust, water droplets and even gas molecules that make up the air itself! And once the light waves interact with these particles, it gets scattered!

For a wave to interact with a particle, the two must be of the same order of size. Smaller particles scatter short wavelength light (blue) stronger. Small air molecules, which make up the entire atmosphere, scatter the blue component of sunlight the most, and in all directions, because of its short wavelength! And this is why, during a sunny day, everywhere you look, the sky is blue!

Do you know why sunsets are reddish? If not, read this article to find out!

Categories
Northern Lights Space weather Universe

Solar Minimums

The 11-Years Long Solar Cycle
The 11-Years Long Solar Cycle

This year is a solar minimum. What does that mean? Can we see the Northern Lights during a year of solar minimum, such as 2020?

Scientists have been monitoring our Sun’s activity since hundreds of years and have observed that it varies periodically. More exactly, the number of the visible sunspots on our star’s surface, increases then decreases periodically, during a period of 11 years. When this number is on the low side – that’s a solar minimum, and we are currently there in 2020. The next solar maximum is expected towards 2025-2026.

Sunspots are associated to high solar activity (solar flares, coronal mass ejections) – which is necessary for Auroras to form here on Earth. But solar activity can also be due to other phenomena, such as coronal holes, which can occur even at solar minimums, and do not depend on the number of sunspots!

So, to answer the last question is the introductory paragraph – “yes”, the Aurora can be seen during years of solar minimums, too! And very well even, as coronal holes can lead to powerful geomagnetic storms!

In addition, places located on the Kp=0 Auroral Oval, such as Vadsø, need a considerably little activity in order to display beautiful Auroras. So, here in our region, the Northern Lights are seen in amazing displays, even in solar minimum years.