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Practice English Speaking&Listening with: Stunning eclipses on celestial bodies in the solar system

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We all know about, and may even have seen a solar eclipse on Earth. A solar eclipse

is a beautiful and spectacular phenomenon where our Moons orbit takes it directly

between our viewpoint on Earth and the Sun. The moon, purely coincidentally, is the right

size and distance from us that its angular diameter is almost identical in size and shape

to the angular diameter of the Sun in our sky. This leaves for an impressive spectacle,

where the corona of the Sun, or in other words the Suns upper atmosphere, creates a ghostly

aura around the Moon. The corona, normally too dim to see, extends for hundreds of thousands

of kilometres into space. Looking closely around the edge of a total solar eclipse,

and you will also see the silhouette of the Moons craters along the outside, plus these

reddish wisps coming off from the Sun. These are prominences, millions of tonnes of charged

particles, suspended in the Suns atmosphere by powerful magnetic fields. But is Earth

the only place in the solar system to experience such solar eclipses? Where can eclipses be

seen? Im Alex McColgan, and youre watching Astrum, and together we will look at the breath-taking

spectacle of eclipses in space. Firstly, Ill quickly explain some of the terminology to

do with eclipses. A total solar eclipse is when an object moves in front of the Sun,

completely obscuring it, also known as an occultation of an object. This is the typical

kind of eclipse we see on Earth, when at certain points in Earths orbit; the orbit of the

Moon aligns with the Sun. The Moon casts a shadow on Earth about 250km in diameter, which

moves across the Earth as the Moon orbits. The Sun will only be totally obscured within

the diameter of this shadow, outside of that the Sun is only partially obscured from the

viewers perspective. This viewer is witnessing an annular or partial eclipse, also known

as a transit. These terms occultation and transit will be important for later in the

video. The shadow moves across the Earth extremely fast, at roughly 1km a second. Witnessed from

a high altitude, it is a majestic sight as the shadow shifts across the landscape. Satellites

have also witnessed the movement of this shadow. The shadow isnt as sharp as you might expect,

and this is due to the angular diameter of the Sun and the Moon, and their distance apart.

The Sun itself is huge, a whopping 1.4 million km across. The Moon is much smaller, at only

3,400km across. Now this image isnt to scale, but it shows visually why the shadow

isnt sharp. The umbra is the shadow where the Sun is completely obscured, and the penumbra

is the shadow where the Moon only partially obscures it. This part of the shadow is much

wider than the 250km wide umbra shadow. So why doesnt the Moon create eclipses every

month when it orbits in front of the Sun? Well this is because the Moons orbit is

not in line with Earths orbit around the Sun. This means there are only a couple of

times per year when the alignment is right. This alignment of three celestial objects

is known as a syzygy, a very cool word but not something youll need to remember for

this video, just thought you would find that interesting! So now you know the mechanics

of an eclipse, we can have a look at where other eclipses take place in the solar system!

Firstly, well stick close to Earth. Because it would make sense that if the Moon can occult

the Earth, then surely the Earth can occult the Moon. And the answer is yes, but its

not the shadow thats the really visually appealing part of this, from Earth anyway.

That is because the Earth is four times as big in the Moons sky as the Moon is on

Earths, so when the Earth fully obscures the Sun, the whole Moon is in the umbra. At

first the shadow of the Earth creates a crescent shape (explain that flat earthers). But what

is different this way around is that unlike the Moon, the Earth has an atmosphere. This

means that when the moon is totally eclipsed, the Earths atmosphere refracts the Suns

light around the planet, gently illuminating the Moon in a reddish hue. This makes for

a beautiful but almost spooky view. The colour is caused by Rayleigh Scattering, a topic

Ive discussed in another video. Rayleigh Scattering is the same process that makes

our sky blue and our sunsets red. This image is beautiful in that you can see the different

wavelengths of light being scattered through the Earths atmosphere, from deep red from

this side through to blue on this side. From the moons perspective, none of the Sun

would be visible during a total eclipse, but the atmosphere on Earth would be illuminated

so you would see a ring around it. This is an actual view of a lunar eclipse on the Moon

by one of the JAXA probes in 2009. It is quite the awe inspiring sight! The Earth and Moon

arent just getting in the way of each other either. Here is the Earth eclipsing the Apollo

12 spacecraft in 1969 while it was on its way back home. And heres the Moon getting

in the way of the Earth from the perspective of the DSCOVR satellite. Interestingly, this

is the side of the Moon you never see, as the Moon is tidally locked to the Earth which

means the same face is always looking towards Earth. From this perspective, the Moon looks

very foreign, but it is indeed a real video of our only natural satellite transiting the

Earth. From another satellites perspective, but this time looking at the Sun with the

SDO satellite, the moon often makes an appearance. This satellite, unlike DSCOVR, orbits around

the Earth, which means the Moon can block the Sun occasionally. And heres the Moon

again, this time from the perspective of one of the STEREO satellites. The Moon isnt

the only thing that orbits between us and the Sun. Mercury often transits across the

Sun, a tiny minnow compared to the solar systems giant. The next time this will happen is on

the 11th Nov 2019, so if you get an opportunity, take a look! Otherwise you will have to wait

until 2032. Venus also orbits between us and the Sun, and as it is much closer to us and

bigger than Mercury, its silhouette appears much larger. Its last transit was in 2004

and 2012, but sadly if you missed those two, chances are that you will never see it. These

transits happen in pairs, and then there is a 100 year gap until the next one, in other

words the next transit will be in 2117. This happens for the same reason the Moon doesnt

eclipse us every month; the orbits just dont often align. Still, we have HD videos of the

last one, and it is quite the sight to behold. Moving to another planet now, we can go to

Mars which has plenty of unmanned robotics either in orbit or on the surface. Mars also

has two moons, Phobos and Deimos. They are both pretty small, Phobos is 22km across and

Deimos is only 13km across. They both orbit very close to the planet though, Phobos is

only 9,000km above the surface and Deimos is 23,000km, which means although tiny, you

can still easily see them from the surface of Mars, especially Phobos. The Curiosity

rover was able to capture a moment where incredibly, Phobos eclipsed Deimos. This video is captured

in real time and shows the size differences of the moons in the Martian sky. And this

is not all the Curiosity Rover captured; it was also able to see a transit of Phobos in

front of the Sun. Due to the distance of Phobos to Mars, it moves across the sky fairly quickly,

only taking about 7 hours to orbit once. This means that this video you are watching is

in real time, and these solar eclipses on Mars dont last for more than about 30 seconds.

The surrounding ground does get noticeably darker during an eclipse by Phobos as can

be seen from the rovers perspective, but it can also be seen from space. Phobos

shadow here can be seen by the Viking 1 orbiter, and also here more recently by the Mars Global

Surveyor. The Opportunity and Spirit rovers have also seen a transit of Deimos, but it

appears much smaller, just a dot passing in front of the Sun. It doesnt cause a noticeable

decrease in brightness. Mars is pretty impressive, but thats not all the solar system has

to offer. Have a look at this video captured by the Hubble Space telescope, looking at

Jupiter. Jupiter has four large moons, three of which at certain points can transit the

planet at the same time, leaving three big shadows. The moons in question in this video

are Io, Callisto and Europa. Interestingly, like we talked about before with the umbra

and penumbra, you can see that because Io is closest to the planet, its shadow is the

sharpest. Whereas you can see with Callisto, the furthest away of these three moons, the

penumbra is much larger, causing a blurry shadow. And in this video, Hubble spies the

occultation of Ganymede, the largest moon of Jupiter. Cassini saw some incredible transits

and occultations of Saturns many moons. Here is one of Epimetheus passing in front

of Titan, with Dione coming in from the side. This little white dot coming in from the left

just under the ring is in fact a bright background star. And this Hubble view is magnificent,

here are Enceladus, Mimas, Dione, and Tethys orbiting Saturn. Once every 15 years, Saturns

rings and moons are aligned just right so that the Moons shadows stream across the

rings as well as on the planet. This video is a timelapse that lasted 9 ½ hours. Amazing.

Going a bit further out, we come to Neptune and its biggest moon Triton. Sadly we dont

have video, but this image captured by Voyager 2 is gorgeous. Three days after passing by

Neptune, Voyager was able to capture the crescents of Neptune and Triton before Neptune slipped

in front of Voyagers view of Triton. Going further out again, we come to the furthest

celestial object explored in our Solar System, Pluto. As New Horizons whizzed by Pluto in

2015, it turned its camera back towards Pluto to capture the dwarf planet totally eclipsing

the Sun. What it saw was dazzling, the sunlight streaming through and illuminating the atmosphere

and its haze layers, with the ridges and mountains on Plutos surface highlighted by the stark

contrast of Plutos night side. Occultations and transits may be breathtakingly beautiful,

but are they actually useful to us scientifically? Well did you know that Uranus was discovered

to have rings because of an occultation of a background star? As the planet orbited in

front of the star from our perspective, the star dimmed before and after the planet obscured

it. With this information, we were able to count how many rings Uranus has. Did you also

know that transits of exoplanets in front of their stars are actually how we can detect

exoplanets? We have telescopes like Kepler that measure the brightness of stars in the

sky. If a star dims, it could be because one of its planets just passed in front of it.

If the star continually dims in a pattern, for instance once every 100 days, then we

know that a planet orbits that star and takes 100 days to do so. And lastly, did you know

the Greeks were able to find out the distance of the Earth from the Sun using eclipses and

shadows? If you want to try this out for yourself, offers a great course on detecting

exoplanets in faraway star systems, and also follows the same mathematical process Aristarchus

took when he discovered the distance of the Earth from the Sun. Astronomy doesnt have

to be a far away and out of reach subject, as actively grappling with these puzzles will

really help you understand the science better, and Brilliant is a great teacher which will

ease you into the maths to make science that much more enjoyable for you. If you go to, you can sign up for free to have a sample of their courses, and

by using that link, the first 200 people will get 20% off the annual Brilliant premium subscription.

If you want to support my channel and also expand on your own knowledge, I highly recommend

this website. Thanks for watching! If you liked the video, the most important thing

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best and see next time.

The Description of Stunning eclipses on celestial bodies in the solar system