A travel guide to Mars
The Hindu in school, 22/09/2014

Imagine a vast barren desert of red dust and rocks, sand dunes swept by the winds, incredible canyons and the tallest mountain of the Solar System. Imagine a world where you could effortlessly jump 3 meters high, climb down steep craters, and set foot on everlasting carbon dioxide ice, that turns into vapour instead of melting. Welcome to planet Mars, one of our nearest neighbours!

Like Earth, Mars orbits around the Sun. But Mars is further away from it, so the Sun appears smaller in the Martian sky. It would take around nine months to reach Mars from Earth, and communications with Earth would be delayed... [READ MORE][PDF]

Faraway, so close
The Hindu in school, 29/09/2014

Have you ever tried to count the stars in the night sky? Have you ever wondered how many worlds like our Solar System could exist in the vastness of the Universe?

Most shining dots you see in the night sky are stars like our Sun. Some are bigger, some are smaller. But they are all part of our Galaxy, the Milky Way. A galaxy is a group of many stars, dust and gas held together by the gravitational force. The same force that holds you to the ground and prevent Earth to escape from the vicinity of the Sun. There are more than hundred billion stars in the Milky Way! [READ MORE][PDF]

Island world in the vastness of the Universe
The Hindu in school, 06/10/2014

All the stars you see in the sky belong to our Galaxy, the Milky Way. But our naked eyes can't see everything: if you point a powerful telescope to any seemingly empty region of the sky, it will uncover hundreds and hundreds of other galaxies! Each of these galaxies is a world in itself, containing billions of stars and planets. Our Milky Way may be huge, but it is only one galaxy amongst hundreds of billions!

The Andromeda Galaxy is one of the nearest galaxies to the Milky Way. But it is already two million light-years away, which means it took two million years for its light to reach us... [READ MORE][PDF]

The earliest light
The Hindu in school, 17/11/2014

When we look at the universe with our telescopes today, we can see stars, galaxies, clusters of galaxies and huge voids between them. As matter gathers around galaxies and leaves big empty regions, the universe is highly inhomogeneous. Have you ever wondered what the universe looked like in its earliest stages?

What we call the Cosmic Microwave Background is the closest we can get to an image of the universe as it was right after the Big Bang, more than 14 billion years ago. It is a light which is not associated to any star or to any other astrophysical object, but rather bathes the entire universe in a background glow. [READ MORE][PDF]

Drifting away from us
The Hindu in school, 01/12/2014

The milky white glow you can see across the sky during dark moonless nights is our Galaxy, the Milky Way. It is made of a myriad of stars held together by the gravitational force, our Sun being only one of them. Although philosophers and scientists had imagined the possibility of a multitude of island worlds like our Milky Way far away from us, it is only in the beginning of the 20th century that this possibility became a scientific fact. All at once, the Universe appeared much wider than initially thought.

Galaxies outside of the Milky Way have in common the fact that the farther they are... [READ MORE][PDF]

The dark side of the Universe
The Hindu in school, 22/12/2014

We are all made of the same building blocks: particles such as protons, neutrons and electrons. All the matter we can see is made of these particles. But what if they were only a small portion of all the matter in the Universe? What if there were other forms of matter? As strange as it may seem, the current model describing the Universe assumes the existence of an unseen type of matter.

Gravity is the invisible bound that makes apples fall towards the ground and satellites like the Moon orbit around the Earth instead of flying away. The Moon is indeed always falling towards us... [READ MORE][PDF]

A nursery for stars
The Hindu in school, 05/01/2015

The Orion Constellation is one of the easiest constellations to identify in the winter night sky, because of three aligned stars that constitute Orion's belt. It represents a giant hunter with broad chest and strong feet from Ancient Greek mythology, whom the gods placed amongst the stars at his death.

Below Orion's belt is an alignment of stars that could represent his sword sheath. This is where one of the most magnificent astronomical objects lies: the Orion Nebula. It can be visible to the naked eye or with binoculars as a faint red glow, but one need a powerful telescope such as... [READ MORE][PDF]

Life and fate of a star
The Hindu in school, 02/02/2015

The warm light of the Sun that basks the Earth has enabled life to bloom on our planet. Our fate is inevitably tied to the fate of our star.

The Sun is an incredibly hot sphere of gas, mainly made of hydrogen, and the temperature in its core can reach millions of degrees. In this unbearable furnace, hundreds of millions of tons of hydrogen atoms fuse together each second to form heavier elements like helium through powerful nuclear reactions. These fusion reactions are very energetic and emit the intense light that would blind you if you were to stare at the Sun for too long. [READ MORE][PDF]

The grand finale of a giant star
The Hindu in school, 16/02/2015

During the summer of the year 1054, Chinese and Japanese chroniclers recorded the apparition of a new object in the sky. It looked like a very bright star, so bright it was even visible during daytime for a couple of weeks. Its luminosity then slowly faded, although the new object remained visible to the naked eye during the night for about two years. Some American Indians carved the event in stone, while a doctor from Baghdad saw it as bad omen and related it to the plague epidemics that had burst in Constantinople and Cairo. In this epoch, people often tried to interpret astronomical events in the light of their own history. [READ MORE][PDF]

An irresistible attraction
The Hindu in school, 09/03/2015

Black holes are among the most fascinating objects in the Universe. How would a journey towards a black hole look like?

When you throw a ball up in the air, it always falls back down to the ground because of the Earth's gravitational attraction. If you throw the ball harder, it will get higher but will still fall down afterwards. The ball can't easily escape the Earth's gravity!

If you could throw the ball at an extremely high speed though, it would escape the Earth's gravitational attraction and continue... [READ MORE][PDF]

A glimpse at the formation of our Solar System
The Hindu in school, 13/04/2015, together with Emmanuel Jacquet

The history of our Solar System probably started 4.57 billion years ago when a fragment of a huge cloud of gas and dust started to contract because of its own gravity, somewhere in interstellar space. While contracting, it became denser and denser, until its core became a star – our Sun. But not all the matter went straight to the Sun...

Rotation plays an important role in the formation of a planetary system like our Solar System. In all likelihood, our parent cloud fragment had some rotation, and this rotation accelerated upon contraction. Have you ever tried spinning on a rotating chair? [READ MORE][PDF]

Meteorites: witnesses of the solar system’s birth
The Hindu in school, 31/04/2015, together with Emmanuel Jacquet

Have you ever seen shooting stars streaking across a clear night sky? These flashes of light often disappear as fast as they appeared, in the blink of an eye... But they actually have nothing to do with stars! Shooting stars, or meteors, are small solid grains entering our atmosphere at high speeds. They are going so fast that the air around them heats up, makes them shine, and usually burns them up.

During its orbit around the Sun, the Earth is constantly bombarded by particles of all sizes, and extraterrestrial stones that make it to the ground are called meteorites. Videos of meteorite falls... [READ MORE][PDF]

Ripples in the fabric of the Universe
The Hindu in school, 16/02/2016

Hundred years after the publication of Albert Einstein's general relativity theory, gravitational waves have been detected directly for the first time. The observed ripples in the fabric of space-time come from the merger of two black holes and open a new window on the Universe.

Our attraction towards the Earth, which makes us stick to the ground instead of flying away, the movements of planets around the Sun or of the Moon around the Earth all have a common origin. While classical mechanics describes it as an invisible, gravitational force, Albert Einstein's general relativity theory explains it as a property of space-time itself... [PDF]

For more informations, contact me at jonathan.freundlich at mail.huji.ac.il