Magnetic Fields: From the Sun

It’s not just the planets that have magnetic fields. The Sun also has a very large and dynamic magnetic field.

The sun’s magnetic field is formed much like on Earth and Jupiter. There are convection cells that bring heat from the sun’s heat sources to the surface. These convection cells, and the sun’s rotation period of 25.4 Earth days produce the sun’s magnetic fields. However, there are many notable differences.

These granules on the sun are convection cells.

The sun is over 12,000 times larger than the Earth, which means that its magnetic fields are larger as well. It’s so large, it extends past the orbit of Pluto. However, it isn’t a solid object, like Earth. The sun’s material is mostly plasma, which works like a gas; like Jupiter. This means that the sun experiences differential rotation, where the equator rotates faster than the poles. On the sun, its Equator rotates every 25.4 days, but its poles rotate every 29 days. This video will demonstrate what that does to the sun.
When the sun rotates, the equator stretchs the magnetic field lines towards the sun’s direction of rotation, and it will keep stretching it until they snap like rubber bands. When they snap, they release the energy in the magnetic field and the magnetic field lines pop out of the sun. These magnetic field lines cause the charged particles from the surface to become trapped along the magnetic field lines. Those trapped particles are called prominences. In addition, Sunspots are formed where the magnetic field lines poke out and in, when the charged particles are lifted from its surface. That is why sunspots are common during periods of high solar activity, like the Solar Maximum.

Eventually, the magnetic field lines will reconnect with each other, and release a lot of energy, leading to large solar flares, and coronal mass ejections. At the same time, the polarity of the magnetic fields will reverse. When the flip is complete, the sun’s magnetic field will drop to zero, reappear in its reversed polarity, and start the process again. This process occurs every 11 years and after each cycle, the poles reverse.

Today, there is evidence that the Sun’s magnetic field is in the process of flipping after a chaotic solar maximum. Once the flip is complete, the process starts again.

Here is a video that talks about the sun and its solar cycle by NASA:



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Coursera Lecture 6.6






Magnetic Fields: Its Purpose on Earth

Hi everybody,

If you have used a compass, then you have used one of Earth’s key features to find your way. That feature is Earth’s magnetic field.

Earth is a giant magnet. This is because the core generates the magnetic field using the process called the geodynamo. The geodynamo process works like this: the outer core is full of conductive metals that is heated from below by the inner core. This drives the convection. The convection in the outer core is maintained by the heat in the inner core, and chemical differentiation. With help by the rotation of the Earth, this drives convection, and creates an instability that forms the magnetic field, and this process aligns the magnetic field to the rotational axis of the planet.

The Geodynamo Process

Magnetic fields are essential for life on Earth. That is because the magnetic field protects the planet from cosmic rays and charged particles from solar flares. When the charged particles hit the magnetic field, they become trapped and slide along the field lines moving towards the poles. The strongest areas of the magnetic field are near the poles, and if the particles are not strong enough, then they are repelled and they bounce back and forth along the field lines and that creates the Van Allen Radiation Belts. There, the magnetic field has trapped the charged particles to prevent them from reaching the atmosphere. If we didn’t have the magnetic field protecting the Earth, then the atmosphere would become stripped of its atoms and the radiation from the solar wind would irradiate all life on Earth.

Van Allen Radiation Belts

However, the charged particles also interact with the magnetic fields. The motions of charged particles in circles form magnetic fields of their own. As a result, when both magnetic fields collide with each other, Earth’s magnetic field absorbs the momentum of the charged particles, and that pushes Earth’s magnetic field back. The Earth wants to make an even magnetic field, but the Sun is pushing the magnetic fields away from the sun. It’s not an even bombardment, due to the variations in solar output.

There are times when the solar wind is strong enough to overcome the magnetic field. The charged particle slides along the field into the poles, and when it is strong enough, it enters the atmosphere near the Earth’s poles, and ionizes the atmosphere. This leads to a beautiful sight called the Aurora Borealis/Australis.

Auroras over the landscape

Earth is not the only planet with a magnetic field though.

Stay tuned for my next post.



Coursera Lecture – Week 5.8





Movement of Planet Earth

Hi Everybody,

Did you know that you would weigh 0.3% more if the Earth was standing still? Probably not, but it doesn’t matter because the Earth does spin. If you look at something on Earth, like a tree, or a house, it seems stationary. However, those objects, like everything else on Earth, are in constant motion. This is because the Earth, and everything on Earth, rotates every 23 hours, 56 minutes, and 4 seconds.

Hold On! We know that a day is 24 hours. How can approximately 4 minutes be missing from a day? Before we answer that, what is this day that has 23 hours, 56 minutes, and 4 seconds? This is called the sidereal day. Sidereal days have 24 sidereal hours which corresponds to a 15 degree movement of the stars per hour with respect to the Earth’s rotation. Basically, a sidereal day is a day with respect to the stars’ fixed positions. For example, if you take the star Deneb, and track its motion for a whole day, it would’ve made a complete 360 rotation after a sidereal day. This has been used since antiquity to determine time. However, why is it that we have 24 hour days, and not sidereal days?

As the Earth rotates, and sidereal days pass, it also moves along its orbit around the sun. If the Sun and Earth were aligned at noon, and a sidereal day passed, the Earth would be out of alignment with the sun. It would need an extra four minutes of rotation to realign it to the sun and reach noon. This is a solar day, and a solar day has 24 hours.

Sidereal vs Solar Day

Sidereal vs Solar Day

Another way to think about it is, as the Sun moves along the celestial sphere(the sky) from east to west, it trails by 4 RA minutes every day. The reason that we have these two standards of time is because, one clock runs 4 minutes fast. If September 21 is our start point, where midnight is 0 hr, 6 months later, on March 21, midnight is 12 hr, or noon. It creates an imbalance in time. It is simpler to have a 24 hr day where noon is noon every day of the year. It is easier to plan your daily events without taking into account the imbalance of time. It’s clear that the orbit of Earth has a profound impact on our day in many ways.

Earth orbits around the sun for one year or 365.25 days. During that orbit, it travels a total of 940 million km in space. Almost all orbits are not circular, but are ellipses. That is true for Earth as well. There are two points in any orbit called: Periapsis, and Apoapsis. (Each body has a different name for their orbital points, e.g. for Sun, Perihelion, and Aphelion). Earth has a perihelion of 147,098,290 km (0.98329134 AU) and an aphelion of 152,098,232 km (1.01671388 AU). On average, Earth has a semi-major axis of 149,598,261 km, which is 1.00000261 AU. This means its orbital eccentricity is 0.01671123, where an eccentricity of 0 is a perfect circle, anything between 0 and 1 represents an elliptical orbit, and anything 1 or greater is a parabolic orbit, or a hyperbolic orbit, respectively. While the orbit is slightly eccentric, this eccentricity doesn’t have much effect on the climate of Earth. It is seen in the fact that when the Earth is at aphelion (farthest point from the sun) in July, the Northern Hemisphere experiences summer, and when the Earth is at perihelion (the closest point to the sun), in January, the Northern Hemisphere experiences winter. The reverse is true for the southern hemisphere. The main reason why there is winter and summer is because of the tilt of the Earth.

During the year, there are four major events that occur: The Winter and Summer Solstices, and the Autumnal and Vernal Equinox. Imagine two lines on Earth, the equator, and the ecliptic. The ecliptic is 23.5 degrees tilted with respect to the equator. This simulation will help you imagine both lines. The equinox occurs when the sun reaches the point where the ecliptic and the equator intersect. At this time, both the Northern and Southern Hemispheres have an equally long day and night. The Solstices occur when the sun, on the ecliptic, is at the highest point away from the equator. At that point, it is angled towards one hemisphere and away from the other. For example, An observer in Canada, on June 21, will see the sun at its highest inclination, whereas an observer in Chile will see it at its lowest inclination. This means that the hemisphere that is tilted towards the sun will experience longer days and shorter nights, whereas the other hemisphere will experience shorter days and longer nights. Click here to see the seasons in action. This process repeats every 365.25 days, but not quite.

While an Earth year is 365.25 days, the definition of a year has been refined over the centuries. Earth has a sidereal year of 365.2564 days. This is the time it takes for the Earth to return to the same position with respect to the sun. For example, starting September 21, 1 sidereal year later, it will be in the same position. Our modern calendar year is 365 days. This is problematic because as these additional 1/4 days accumulate, it will add up and cause problems. Every four years you are off by day. After 720 years, you have 180 extra days, and that means January is summer in Northern Hemisphere, which is a problem if you are keeping time. Luckily, Julius Caesar was able to figure that out and is able to legislate the leap year. He has introduced the leap year, and as a result, we never drift more than a day. However, that is not enough.

Our calendar doesn’t drift more than a day, but it still doesn’t match the seasons. The calendar does take into account the length of the year, and the tilt of the Earth, but it doesn’t take into account the precession of the axial tilt. This precession causes the Earth’s tilt to rotate westward ever so slightly. This means that Polaris won’t be our north star forever. This precession completes its rotation every 26,000 years. While the effect is quite insignificant, it does affect our calendar, because year after year, the precession shortens the time between seasons. This results in the tropical year, which has 365.2422 days, which is slightly shorter than a sidereal year. As a result, to account for the axial precession, Pope Gregory XIII, in the 16th century, corrected for the difference between the sidereal year and tropical year by removing the leap years of centuries not divisible by 400. For example, years 1700, 1800, 1900 do not have leap years, but 1600, 2000 do have a leap year. This correction, and the tropical year is what the Gregorian calendar is based on, and this calendar allows our timekeeping to remain consistent for many years to come.

The path of Earth’s axial precession

What the precession looks like.

So what did we learn today? We learned a lot about the movement of Earth. We learned about what is a sidereal day, and what makes it different from a solar day. We learned about the orbit of Earth and what occurs during that orbit. We also learned about what makes our calendar the way it is today. I hope you all found this interesting.

Stay tuned for more blog posts…



Coursera Lecture – Week 1.4 – 1.7, 1.10


VIDEOS USED – NASAEarthObservatory

About Our Planet Earth

Hi everybody,

It’s an amazing thing to look into the sky and look at the other worlds that exist. However, it all starts on the planet that we know the most about: the planet Earth.

Earth from Apollo 8

Earth from Apollo 8

Earth is a rocky planet located in the Solar System. It is the third planet from the sun. It is the most dense planet in the solar system, and the only planet to support life. It has one natural satellite, The Moon, and many other artificial satellites sent up by humans. It has a mass of 5.97219E24 kg, and orbits 1 AU or 149,597,870,700 m from the Sun.

Believe it or not, Earth is the only object with a name that doesn’t originate from Greek/Roman mythological figures. If it were, it could’ve been called Tellus (not Telus!) or Gaia, using Roman or Greek names respectively.

Planet Formation

Earth was formed during the formation of the Solar System. It is 4.5 billion years old. During its formation it accreted many smaller asteroids and planetesimals to form a protoplanet. In Earth’s early history, it is conjectured that a mars-sized protoplanet collided with the Earth and released all kinds of silicates into orbit which accreted to form the Moon. When the moon formed, it was really close to the Earth. As the system orbited the Sun, the Earth and Moon exchanged angular momentum, which slowed Earth’s rotation period and pushed the moon’s orbit outwards. This resulted in today’s Earth and Moon system.

Formation of a Moon

Atmosphere of Earth with Moon in the background

The planet’s atmosphere is 77% Nitrogen (N2), and 21% Oxygen (O2), with traces of other gases. Earth has a lot of free N2 in the atmosphere because it couldn’t form rocks with Silicon, Calcium, Sodium, and other elements to form rock, unlike O2 which formed rocks with these elements. In addition, N2 is quite stable, even under the influence of solar radiation. It has built up over time, unlike O2, which is consistently being recycled in Earth. In the past, the atmosphere, most likely, had a lot more Carbon Dioxide (CO2) than now. This was due to Earth’s formation. However, when water was introduced in the atmosphere, the raindrops was able to lock the CO2 in carbonate rocks, absorb inside the ocean, and eventually was used in photosynthesis. Now, there are traces of CO2 and it is increasing due to industrial processes, however, these traces (before and after human pollution) help trap heat to keep the climate in check using the greenhouse effect. It is also that same reason why Venus is the hottest place in the Solar System.

Earth’s Interior

The Earth has many layers. Earth has a crust, upper mantle, lower mantle, an outer core and an inner core. We learned about these layers by using sound waves. As one goes downards to the core, it gets hotter and denser. The reason the core is so hot is because the core generates heat using radioactive decay 80% of the time, and Kelvin-Helmholtz processes 20% of the time. The heat is transferred to the top by using circulation cells in the mantle. The core and outer core are made up of heavier elements, like iron, and nickel, whereas the mantle and crust is made up of lighter silicate materials. This is because, when Earth, during its formation, accreted enough mass, the heat of collisions and radioactivity causes the Earth to melt, and then the process of chemical differentiation takes place. The heavier elements sink towards the centre, whereas the lighter elements float to the top. This occurs when planetesimals becomes protoplanets. Today, due to plate tectonics, erosion, and other processes, most of Earth’s geologic history has been erased.


As far as we are concerned, Earth is the only planet that can support life. It is predicted that Earth’s biosphere started to form 3.5 billion years ago. Once life moved into land, the biosphere became divided into different biomes. The type of biome depends on its latitude, height from sea level, and humidity of area. For example, humid lowlands at equatorial latitudes produce very diverse biomes whereas extreme latitude, high height, and extreme humidity produce different biomes. In Earth’s history, there have been five major extinction periods, with the most recent occurring 65 million years ago, killing off all the dinosaurs. Eventually, the mammals diversified and a certain ape-like species of animal evolved to stand upright, and it eventually led to the evolution of humanity. Today, humans have evolved greatly with various innovations and technological advancements. In addition, the search for life beyond our solar system is increasing at a rapid pace. Astronomers, scientists, and looking at other stars and finding exoplanets that have the potential to support life.

Stay tuned for more information about our planet Earth.


Images used