Tag: Sun

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Science Stargazing Universe

Solar Eclipses

Solar eclipses are dramatic events
Solar eclipses are dramatic events

A solar eclipse occurs when the Moon, in it’s own movement, finds itself between the Earth and the Sun. One of the consequences of this alignment will be the blocking of a part (or all) of the Sun’s light here on Earth, in areas where the eclipse is visible. This is due to the fact that the Moon covers the Sun’s disk partially, or sometimes even totally.

Solar eclipses can thus be of two types: partial (when the Moon covers only part of the Sun’s disk) or total (when the Sun’s disk is covered completely by the Moon).

Total Solar eclipse

A total solar eclipse, which is the most dramatic – because the sky turns dark just like at night for a few minutes during mid-day – is much more rare, as the conditions needed for such an eclipse to occur, are much more strict.

For a total eclipse to occur, the Moon needs to be closer to the Earth on its elliptical orbit, so that its apparent size can be large enough to cover the Sun’s disk. In addition, the totality (the period of only a few minutes when the Sun is completely covered by the Moon) occurs only along a very narrow path along the Earth’s surface.

Annular and partial Solar eclipses

So, most of the Solar eclipses are not total!

But even if the Sun’s disk is not covered completely by the Moon, the concentricity of the two disks can create another beautiful Solar eclipse – an annular one, when the Sun is visible around the moon, just like a ring – hence its name!

However, most of the times a Solar eclipse will be partial, when the Sun’s disk will be partially covered by the Moon, and not in a concentrical manner. This is the most common type of Solar eclipse that we see.

Visibility of a Solar eclipse

One solar eclipse (be it partial, annular or total) can’t be visible from everywhere on Earth. The Sun needs already to be visible – which narrows down the visibility of an eclipse to less than half of our planet! As the relative positions of the Moon and Sun in the sky, seen from our planet, are always changing, the alignment of the two for an eclipse to occur, narrow its visibility down even more.

Sizes of the Sun and the Moon

The Sun is much bigger than the Moon, that’s for sure. So how can it be completely covered by the Moon then?

To answer this question, we need to look at the distance of the Sun and Moon, from us, from our planet. The Sun is much more far away from Earth than the Moon is! Which makes it have an apparent size more or less equal to the apparent size of the Moon! The Moon moves along an elliptical orbit around Earth, which makes it, at times, be closer to our planet. Which translates itself into a bigger apparent size of the Moon, which actually becomes slightly larger than the Sun’s apparent size. Which finally, can lead to a total Solar eclipse, if the other conditions for this event to occur, are met!

Looking at an eclipse

Warning! Never look at a solar eclipse with the naked eye. Not even sunglasses aren’t enough! In order to see a solar eclipse, you need a special solar filter, which makes it safe to look directly at the Sun. Otherwise, you risk getting extreme eye damage, and even blindness!

The Annular eclipse of 10 June 2021

On June 10 this year, an annular solar eclipse is scheduled to occur! The actual annular eclipse will be visible from a narrow band along Earth, which crosses the North Pole and a few far-North regions of Canada and Russia.

In the rest of the Northern Hemisphere, the eclipse will be a partial one and will be visible from places such as the Eastern part of the US, almost the whole of Europe and parts of Asia.

If, by any chance, you’ll find yourself in Vadsø, you will see a partial Solar eclipse, with a maximum obscuration of 51%, occuring at 13:09, Norway time.

For other location and times, check out this map from NASA to see exactly where on Earth the eclipse will be visible from, in 2 days!

And by the way, did you know that with Aurora Labs you can discover the mysteries of our own Sun by observing it through our telescope? The eclipse seen through a telescope (with a special solar filter, of course!) is a magnificent sight!

A partial solar eclipse.

Update June 10, 2021:

The beginning of the partial solar eclipse on June 10, 2021.

Categories
Nature Science Universe

The Polar Day

The Midnight Sun shines 24/24h during the polar day
The Midnight Sun shines 24/24h during the polar day

Regions way above the Polar Circle, in the High Arctic, have already started to experience the polar day. Other Arctic regions are going to experience the phenomenon in the coming days. In Vadsø, the polar day already started on May 17 this year, and the Midnight Sun has been visible since, as well.

But what is the polar day?

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 summer solstice (sometime around 22nd June each year), Earth is inclined in such a way that the North Pole and the region around the North Pole, points towards the Sun, thus it is illuminated more and longer.

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

The Midnight Sun

The Midnight Sun is a wonderphul phenomenon. It is what makes the sky bright at “night time” during the polar day, just like the Northern Lights brighten the sky during the dark period. It is a typical Arctic (and Antarctic) phenomenon, which occurs only during the polar day.

As the name suggests, here in the Arctic, the sun is visible in the sky at midnight, as well as the whole night and day, and it never sets below the horizon during this period. In Vadsø, the Midnight Sun will be visible this year until July 26.

And did you know that Aurora Labs has a special activity dedicated to discovering the midnight sun differently? Check it out here!

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

And, by the way, the opposite of the polar day is the magnificent polar night! Have you ever experienced one or the other?

During the polar day, the Sun never sets below the horizon.
Categories
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 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!