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Nature Science Stargazing Universe

The Lyrids Meteor Shower

Shooting Star
Shooting Star

Stargazers (almost) all around the world, get ready for an amazing stargazing event which starts tomorrow: the Lyrids meteor shower! Keep on reading to discover what a meteor shower is, and to find out how to see the Lyrids and other interesting facts about them! And don’t forget to prepare your wishes – maybe they will get granted, once you see the Lyrids!

What is a meteor shower?

A meteor shower on Earth usually occurs when our planet’s path intersects with the orbit of a comet. When a comet approaches the Sun, some of its ice vaporizes, leaving behind a stream of dust and debris, called a “dust trail” (which is different from a comet’s tail). When such debris – called meteoroids or micrometeoroids, in function of the size, and which is most of the time the size of a grain of sand -, enters Earth’s atmosphere at very high speeds (typically 70 km/s), it heats up because of the friction with the air in the atmosphere, which causes the particles to light up and glow. This streak of light crossing the night sky is called a meteor, or shooting star. So no, a shooting star is not a real “star” 😉

Meteors usually occur in Earth’s atmosphere at an altitude of above 50 km, and under 100 km. The glow can be fainter and shorter for smaller particles and it becomes brighter and longer as the size of the particle increases. The colour of a meteor can also vary, in function of the chemical composition of the particle!

And, by the way, a meteor that doesn’t burn up and which finally hits Earth’s surface, is called a meteorite!

The radiant

What is very interesting is the fact that the meteor particles in a meteor shower originate from a point called the radiant, and are all travelling in parallel paths.

But if we look at the sky, we see the meteors radiate in all directions. So how can this be? This is the effect of perspective! For example, if you sit in the middle of a straight railroad track and you look along it, you see that the two tracks converge at a single point, somewhere far away. This is exactly what happens with meteors in a meteor shower, but the effect is a lot more intense, due to the great distances where the meteor shower occurs!

The two parallel tracks seem to converge at a single point.

The Lyrids

The Lyrids are a meteor shower starting on April 16 and lasting until April 26 every year. This spring, its peak will be on April 22, so make sure you go out around this date, if you’d like to see this meteor shower in all its beauty; weather permitting, of course!

To locate the radiant of the Lyrids, you will need to find the Lyra constellation in the night sky. It’s not so difficult to find it, as Vega, the brightest star of this constellation, is one of the brightest stars in the night sky, with a magnitude of around 0, thus easy to see even in light polluted areas.

One way of easily finding Vega, is by drawing an imaginary line between two stars forming the well-known Big Dipper asterism, as shown in the below image:

Extend this imaginary line in the arrow’s direction, until you reach your first (very) bright star, which will be Vega. Be sure not to extend the line too long, as you will reach another quite bright star – Altair.

However, to see the actual meteor shower, you would need to find a place away from light pollution, as the shooting stars are not as bright as Vega! Their magnitude average somewhere towards the value +2, sometimes culminating with “Lyrids Fireballs”, which is the name given to some brighter meteors of this event. In addition, the Moon may make it more difficult to see this year’s Lyrids, so, if our natural satellite is troublesome, just wait for it to set, before trying to spot the meteor shower.

Naming and predicting meteor showers

Meteor showers are named in function of the constellation where they originate. So, the Lyrids seem to originate in the constellation of Lyra, hence their name!

The source of the dust creating the Lyrids comes from the C/1861 G1 Thatcher Comet – a long-period comet (415 years).

The Lyrids is a predictable event – that is, they occur because of the crossing of Earth’s path with the orbit of the aforementioned comet, which was last visible from Earth in 1861, when it was discovered by A. E. Thatcher (and is expected to be seen again in 2283!). The intersection of Earth with this comet’s orbit occurs each year in April, thus, the Lyrids meteor shower is then expected!

Did you know?

The Lyrids are the oldest reported meteor shower – since 687 BC!

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Nature Science Universe

The Polar Night

Polar Blue during the Polar Night in Vadsø
Polar Blue during the Polar Night in Vadsø

This period of the year means the beginning of the end of the Polar Night for regions in the Arctic. The polar night in Vadsø will end on the 17 of January, when the Sun will rise for the first time this year in the Arctic sky, for only 50 minutes. After this date, each day will mean the Sun will come out higher and higher in the sky and for longer periods. And this until May 17, when the Sun will never set for almost 2 months, marking the beginning of the Polar Day.

But what is the polar night?

Earth carries out two types of rotations: one around the Sun, during the course of a year, and the second around its own axis, during 24 hours. At the same time, Earth is inclined in respect with the Sun, at an angle of approximately 23°, and remains tilted at this angle during the whole year.

This means that the Earth is illuminated by the Sun differently during one year. At and around the winter solstice (sometime around 22nd December each year), Earth is inclined in such a way that the North Pole and the region around the North Pole, points away from the Sun, meaning it is not illuminated by our star, which translates into a continuous night – phenomenon which we call the Polar Night.

Just take a look at the first part of this video from the California Academy of Sciences, and see how Earth is illuminated by the Sun during a whole year.

You can see that the length of the polar night varies in function of latitude: closer you are to the North Pole, longer the polar night is. At the exact location of the North Pole, the polar night lasts no less than 6 months! At lower latitudes, but still above the Arctic Circle, the Sun never rises for shorter periods. The shortest polar night occurs on regions exactly on the Polar Circle (at 66°N), where the Sun never rises for only 1 day, which is exactly the day of the Winter Solstice!

Moreover, in function of latitude, the Polar Night may be experienced differently, concerning the position of the Sun below the horizon. This means that during the polar night, closer to the Arctic Circle, the Sun will still be near the horizon (but still below it) during the normal “day” hours. Which means that twilight occurs – thus indirect light from the Sun beautifully illuminates these regions, and you are able to see the landscape and the surroundings. And it does it in a surreal blue lighting – which is what the amazing polar blue is! Vadsø in Northern Norway experiences this phenomenon during the whole period of the polar night.

Me during the Blue Hour outside of Vadsø, during the polar night
Dogsledding in the Varangerhalvøya National Park, during the Polar Night

Further up from the Arctic Circle, the Sun does not have time to get so close to the horizon, which means that no indirect light will illuminate these regions at all, which leads to a 24-hour long pitch-black night, which can last for months!

And the best part about the Polar Night? You can see the Northern Lights even during the “daytime”!

Regions below the Polar Circle experience a normal day/night cycle, which varies also in length, in function of the exact latitude.

Categories
Nature Stargazing Universe

See the “Bethlehem Star” in the Night Sky

The Great Conjunction of Jupiter and Saturn occurs on 21 December 2020.
The Great Conjunction of Jupiter and Saturn occurs on 21 December 2020.

In astronomy, a conjunction means the “meeting” of two planets in the night sky. Jupiter and Saturn, the biggest planets in our Solar System, can meet as well, but when they do, their conjunction is a “great” one – hence the term Great Conjunction!

Jupiter and Saturn are one of the brightest objects in the night sky. They look just like two very bright stars – but don’t mistake them for stars! They are planets, so they don’t create light themselves just like the stars (like our Sun does for example). They are “lit” only because of the reflection of the sunlight. Which is the same reason why the Moon shines in the night sky!

The Great Conjunction of 2020

In their perpetual movement around the sun, it happens sometimes that planets “meet”. The word “meet” is quoted because the planets don’t actually meet in reality. It is just how we see things from here on Earth. In fact, the two planets are aligned in such a way in their orbits, that from Earth, we see them as if they came into contact with eachother. In reality though, they’re some million kilometres apart!

And why is this conjunction “great” you may ask? Well, this is because Saturn and Jupiter, due to their size, they are already bright even when they’re “apart”. When two bright lights touch each other, they are seen like only one light, even brighter! The same happens with the conjunction of Jupiter and Saturn.

When does it happen?

Jupiter and Saturn are already close in the night sky since quite some time now. But on December 21 (thus tomorrow!), the two planets will be so close (less than 0.1 degrees) that they will look like an elongated, very bright star. So, stargazers, get ready for a Christmas treat!

Why is the Great Conjunction so special this year?

The Great Conjunction occurs regularly, roughly every 20 years. But why is it so special this year?

In function on the position of the “meeting” with respect to the position of the Sun, the conjunction may be more or less bright. If this meeting place is too close to the Sun, the brightness diminishes. This year, the position is ideal for a very bright Great Conjunction!

Another thing to take into account is how close the two planets will appear to be. Not every 20 years the planets have such an apparent closeness! In fact, to get an idea of how rare this occurs, know that last time Jupiter and Saturn appeared so close, was in year 1226! It actually happened in 1623, but it was rather close to the Sun, which made it actually less visible.

Where and how to look?

You need to look in the night sky about 1 hour after sunset, almost anywhere on Earth, even in light polluted areas! In the Northern hemisphere look towards south-west. As for the Southern hemisphere, look towards the west. Needless to say that you will need a clear sky!

It will be impossible to miss such an impressive sight so, don’t worry, it will not be difficult to spot it!

“Christmas Star”

As the Great Conjunction this year happens very close to Christmas, it is also called the “Christmas Star“, or the “Bethlehem Star“. To go even further, some astronomers believe that the Star of Bethlehem which led the Three Wise Men to the place where Jesus was born, might have actually been a Great Conjunction! But there are other theories that suggest that a supernova might have occurred that time. Or, was it indeed a divine miracle?

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Nature Science Stargazing

Twilight Occurrence

Civil twilight in Vadsø
Civil twilight in Vadsø

In a previous article we saw what is twilight and what are the main types of twilight. As a reminder, twilight is the period of the day when a certain point on Earth is illuminated indirectly, by sunlight scattering, when the Sun is below the horizon, but not more than 18°, thus its rays are still visible, indirectly, for an observer located at that certain point.

Now, we’re going to look at how twilight occurs on Earth, when it occurs and… how it doesn’t occur at all in certain places!

Standard twilight occurrence

A standard twilight occurrence was described in our previous article:

During the course of a day, at sunrise, the Sun appears in the sky from the right (East) and, during the whole daytime, it shines its light directly onto the place on Earth where the observer is located. In the evening, at sunset, the Sun will again reach 0° on the left side (West) and it will slowly disappear under the horizon. This moment the evening twilight starts. Due to earth’s rotation, the Sun will continue to descend more and more under the horizon. But before our star reaches 18° under the horizon, there will still be distinguishable light from the Sun for the observer. When the Sun reaches 18°, dusk occurs, and the observer will not distinguish any indirect sunlight anymore and the astronomical night starts.

Because of Earth’s rotation, the Sun continues its trip and, very early in the morning, before it rises, it will reach again 18° under the horizon. At this moment, dawn occurs, and twilight starts again – this time we’re talking about the morning twilight. As time passes more, the Sun will ascend more, until it reaches again 0° and it rises the next day.

Twilight occurs thus during both periods of the day when the Sun is between 0° and 18° under the horizon.

This scenario is true for people living on Earth between approximately 50° North or South of the Equator at any time of the year. This is also valid for higher latitudes, but not around the summer solstice, when the Sun does not descend more than 18° under the horizon during the “night”, and thus there’s no real astronomical night between dusk and dawn.

Continuous twilight between sunset and sunrise

As written in the previous paragraph, above latitudes of approximately 50°N/S, around the date of the summer solstice, the Sun does not descend lower than 18° under the horizon, which means that, even if the Sun is under the horizon, its rays can still be seen, indirectly, during the whole night, which translates itself into a continuous twilight during the whole “night” hours.

In function of the latitude, there can be a continuous astronomical twilight, a continuous nautical twilight, or a continuous civil twilight between sunset and sunrise. This actually occurs in very popular and accessible places around the world, such as:

  • Continuous astronomical twilight: many European countries, such as northern UK, Ireland, the Netherlands, Germany and many other in the Northern Hemisphere or the Falkland Islands in the Southern Hemisphere;
  • Continuous nautical twilight: a great part of Russia and Canada, northern Denmark in the Northern Hemisphere or Ushuaia in Argentina in the Southern Hemisphere;
  • Continuous civil twilight: more northern parts of Russia (such as Sankt Petersburg), Northern Norway, Northern Sweden, Northern Finland.

White nights

A continuous civil twilight between sunset and sunrise is called a white night. The term white night also applies if a certain place does enter nautical twilight also, but if the Sun does not descend lower than 7°.

The white night constitutes a popular symbol for Sankt Petersburg in Russia, where, around the summer solstice, the Sun never goes lower than 7° under the horizon for several days.

A continuous nautical or astronomical twilight does not mean a white night occurs.

No astronomical day between morning and evening twilight

Within the two Polar Circles – Arctic and Antarctic – in wintertime, Polar Night occurs. The polar night means that the Sun does not rise above the horizon at all during 24 hours. But it may approach the horizon, above 18°, thus its rays are seen indirectly and twilight occurs during the “daytime” hours.

Again, in function of the actual latitude, during the normal “daytime” hours, there may be a continuous civil, nautical or astronomical twilight. Vadsø experiences a continuous civil twilight between approximately November 25 and January 17.

Church of Arctic Sea in Vadsø, at noon, during the Polar Night
Church of Arctic Sea in Vadsø, at noon, during the Polar Night’s daytime civil twilight

No twilight at all

In polar regions, around the summer solstice, the Sun is up in the sky 24 hours a day, a period known as the Polar Day. The Sun that never sets for more than 24 hours is called the Midnight Sun, and it never disappears under the horizon for several days in a row. Higher the latitude, longer the period the Midnight Sun occurs.

As the Sun never goes under the horizon, these places experience no twilight at all during all these days.

This condition occurs here in Vadsø during the Midnight Sun period, and lasts more than 2 months, between approximately May 16 and July 26 each year.

Categories
Nature Science Stargazing

Twilight

Me on the shore of the Varanger Fjord, during twilight
Me on the shore of the Varanger Fjord, during twilight

This is not an article about the famous TV show with vampires! In the next few minutes we’ll talk about what the actual twilight period of the day is, when and how it occurs, and what each type of twilight looks like.

What exactly is twilight?

Twilight is the period of the day when a certain point on Earth is illuminated indirectly, by sunlight scattering, when the Sun is below the horizon, but not more than 18°, thus its rays are still visible, indirectly, for an observer located at that certain point. The lower the Sun is below the horizon, the dimmer the twilight. When the Sun reaches 18° below the horizon, the sunrays’ brightness is gone completely and the “real” pitch-black nighttime starts. (Of course, when talking about the Sun being “18° under the horizon”, we mean its “geometrical centre!”)

The image below presents schematically an observer, his line of sight and the position of the (geometrical centre of the) Sun, at various times of the day:

During the course of a day, at sunrise, the Sun appears in the sky from the right (East) and, during the whole daytime, it shines its light directly onto the place on Earth where the observer is located. In the evening, at sunset, the Sun will again reach 0° on the left side (West) and it will slowly disappear under the horizon. This moment the evening twilight starts. Due to earth’s rotation, the Sun will continue to descend more and more under the horizon. But before our star reaches 18° under the horizon, there will still be distinguishable light from the Sun for the observer. When the Sun reaches 18°, dusk occurs, and the observer will not distinguish any indirect sunlight anymore and the astronomical night starts.

Because of Earth’s rotation, the Sun continues its trip and, very early in the morning, before it rises, it will reach again 18° under the horizon. At this moment, dawn occurs, and twilight starts again – this time we’re talking about the morning twilight. As time passes more, the Sun will ascend more, until it reaches again 0° and it rises the next day.

Twilight occurs thus during both periods of the day when the Sun is between 0° and 18° under the horizon.

In function of the position of the Sun below the horizon during twilight, due to the difference of indirect illumination, we distinguish three types of twilight:
● civil twilight – when the Sun is between 0° and 6° under the horizon,
● nautical twilight – when the Sun is between 6° and 12° under the horizon,
● astronomical twilight – when the sun is between 12° and 18° under the horizon.

Civil twilight

Civil twilight at the border of Vadsø Municipality

Evening civil twilight occurs right after sunset and it lasts until the Sun reaches 6° under the horizon. Morning civil twilight occurs before sunrise, when the Sun is 6° and less under the horizon.

During civil twilight, there’s enough indirect light from the Sun so that artificial illumination is not needed. Objects and landscapes are still visible to the unaided eye. This period is especially sought for by photographers, as the lighting creates an amazing effect in pictures. In polar regions, this is when you can experience the beautiful polar blue.

The first bright stars and planets appear in the sky during civil twilight. Venus is usually seen at this time, hence its name “evening star” or “morning star”.

Nautical twilight

Long exposure photo during nautical twilight

Evening nautical twilight occurs when the evening civil twilight ends, thus when the Sun is lower than 6° below the horizon, and it lasts till our star reaches 12° under the horizon. In the morning, nautical twilight occurs when the Sun is 12° below the horizon and until morning civil twilight starts.

The name “nautical twilight” comes from the fact that sailors could still distinguish a visible horizon at sea, and they were still able to navigate thanks to the brightest stars that are perfectly visible in the sky during the nautical dusk. When not at sea, in places where light pollution is absent and when certain atmospheric conditions are met, the unaided human eye may still distinguish shapes or silhouettes of objects.

Long exposure of a nautical twilight scene, on one of Vadsø’s streets

Astronomical twilight

Evening astronomical twilight occurs when the Sun is below 12° relative to the horizon and just before the astronomical night starts – thus when the Sun reaches the 18° point under the horizon. In the morning, astronomical dawn marks the time when the first indirect sunrays appear and until the morning nautical twilight starts.

The end of the evening astronomical twilight marks the moment when the faintest stars and other faint astronomical objects become visible. And, of course, they will stay visible until astronomical dawn. The unaided human eye will generally not be able to detect any light however, and it will consider the sky entirely dark.

***

In the next part, we will look at how twilight occurs in different locations on Earth. Did you know that, here in Vadsø, when the Polar Night starts (around 25 November each year), we experience a continuous civil twilight from around 8 o’clock in the morning and till around 14h? Find out other cool twilight facts here!