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

Astronomical Events for March 2014

Hello everybody,

Here are the astronomical events occurring in the month of March: (All times are given in UTC format)

       Astronomical Events

  • Unlike February, where there was no New Moon, this March there will be two new moon. The second new moon of the month is a Black Moon. It is the opposite of a Blue moon, which is when two full moons occur during the same month.
  • March 7: Asteroid 9 Metis will occult a +7.9 magnitude star. It will be visible in Europe at 3:14 UTC.
  • March 9: Daylight Saving Time begins. Time to move clocks forward 1 hour.
  • March 10: The Waxing Gibbous Moon occults the +3.6 magnitude star Lambda Geminorum for North America in the evening sky.
  • March 14: Mercury reaches its greatest morning elongation at 27.5 degrees west of the Sun shining at magnitude +0.1. Mercury will look its best at this day during 2014 for observers in the southern hemisphere. It will start to descend again at this time.
  • March 16: A double shadow transit of Jupiter’s moons will occur from 21:20 to 21:30 UTC. This will be visible from Atlantic Canada after the sunset.
  • March 20: The Vernal Equinox will occur at 16:57 UTC. Both hemispheres will experience equal day and night. The northern hemisphere is heading into summer. The southern hemisphere is heading into winter.
  • March 20: GEO satellites will start to be eclipsed by the Earth’s shadow, during the equinox.
  • March 20: This is a very rare sight indeed. An asteroid 163 Erigone will pass in front of the bright star Regulus. It’s easily visible in many places unless it is heavily light polluted. During this time, the asteroid will pass in front of the star, blocking the light from the star for up to 14 seconds. It’s a subtle event, but rare indeed. This will occur at around 6:07 UTC. It will be visible for observers in Eastern US and Ontario, Canada. For Canadian and American observers, it is going to occur around 2:00 am EST. Get there early to set up, for you might miss it completely.
    In addition, some might try to see if 163 Erigone has any moons. To try and find moons, one would need to be at the edge of the shadow, and look for secondary dips in light. To see the map of the shadow’s path, go to:
    For more information about the occultation, go to
  • March 21: The Moon will occult Saturn at approximately 3:18 UTC. This will be visible from the South Atlantic.
  • March 22: Venus reaches its greatest morning elongation, at 47 degrees west of the sun. This will be the best time to view Venus before starts to descend towards the sun.
  • March 24: A double shadow transit of Jupiter’s moons will occur from 1:08 to 1:28 UTC. It is best seen in Eastern North America.
  • March 24: Asteroid 172 Baucis will occult a +6.7 magnitude star. It is visible from South America at approximately 9:27 UTC
  • March 28: Asteroid 51 Nemausa occults a +7.7 magnitude star. It will be visible in Africa at 20:02 UTC.
  • March 30: The Black Moon will occur at this time. This will be the second new moon of the month.

         RASC Toronto Centre Events (These times will be written as EST or EDT)

  • March 3, 2014 – March 6, 2014: There will be a city star party in Toronto. This event allows people living in the city to get a chance to see the planets, stars, and other celestial objects in the sky. It usually takes place in Bayview Village Park, but sometimes it occurs in High Park. Telescopes are not mandatory. Come with an eager interest to see the heavens. This event is weather-dependent though. Go to to look for the GO/NO GO Call the day of the event. During the days posted, there will be a GO/NO GO call. If it is a NO GO call, the event is deferred until a GO call is given. If there is not a GO call given, then the event is cancelled until next month. Otherwise, it is a GO.
  • March 5, 2014 – 7:00 to 10:00 pm: There will be a lecture at York University about the Square Kilometer Array Telescope. The speaker is Dr. Michael Bientenholz. Anyone can attend, and it is free.
  • March 8, 2014 – 6:00 – 10:00 pm: There will be a members imaging night for RASC members. This nights theme is Image Satellite Passes and Auroras. At these events, there is socialization, guest speakers, and if the weather is friendly, a chance to observe the night sky. It is free, but only for members of RASC.
  • March 19, 2014: There will be RASC’s monthly recreational night at the Ontario Science Centre. There will be 5 speakers talking about various topics. This event is free and anyone can attend. Parking is free after 6 pm.
  • March 20, 2014: There will be a public planetarium show at the University of Toronto. There, they will be teaching about the planets, and the interesting discoveries made about them. The public is welcome to the event. There is a $5 door fee to get in.
  • March 21, 2014: Dr. Neil deGrasse Tyson will deliver a free lecture at 8 pm at the University of Toronto. At this event, Dr. Tyson will also be receiving the Dunlap Prize for his efforts to communicate astronomy to the public. The lecture is free, but registration is required. Everyone can attend.
  • March 22. 2014: RASC is hosting it monthly member’s night. Before the event starts, the members socialize. After, we listen to lectures given by our members. And after, weather permitting, we watch the night sky. It’s a free event, but it’s for members only.
  • March 24, 2014 – March 27, 2014: There will be a window open for a dark sky party at the Long Sault Conservation area east of Toronto. In this dark sky, visitors have the chance to truly see the dark sky objects that most people don’t always see. This event is free, and open to the public. However, it is weather dependent. Go to for the GO/NO GO call. If there is a GO call, the event will begin at 8 pm.
  • For more information go to

If you have any questions, you can send me an e-mail with the Contact Forms.

This month I will post more articles about our planet Earth. Stay Tuned!



The RASC Members event at the DDO

On Saturday, January 25, 2014, braving the bitter cold, the Royal Astronomical Society of Canada (RASC) hosted a members’ night for all the members at the David Dunlap Observatory (DDO). At these events, the members get together, socialize, listen to the planned lectures based on the theme of the event, and, if conditions permit, then observe the night sky. These events are hosted every month on Saturday evenings. This month’s theme was “Our Galactic Neighbours”.

I arrived at around 6:00 pm. Once I came in and found the gathering place, I met the members who were present. From the moment I arrived, until the time when the lecture started, I socialized with many of the members present. It was great to meet with a very diverse group of astronomers, teachers, academics, and other members.

At 7:30 pm, the lectures began in the presentation room. As per the theme of this member’s night, all the lectures were about galaxies.The first lecture that was presented to us gave a general overview of what a galaxy is, what we know about them in the past and now, their shape, and composition, satellite galaxies and other cosmological phenomena, such as black holes, dark matter, and dark energy. The second lecture given to us talked about distances with respect to galaxies. For example, We looked at the distances to our immediate neighbours. The Milky Way is 100,000 lightyears (lyrs) across, and M31 (Andromeda Galaxy) is 2.58 million lyrs away. Eventually, we start to expand our horizons and look further out seeing many galaxies clustered together, such as the Virgo supercluster, and when we expand our horizons further at a distance of 400 Mlyrs (Mega-lyrs) across, we see voids in the clusters 100 Mlyrs across. It was very intriguing.

Our final lecture talked about how we can observe deep sky objects ourselves. He gave us tip and tricks to help us identify what we see, how we can best see deep sky objects from Earth with proper positioning of our telescope and our eyes, and the obstacles we will face when observing deep sky objects.

After the lectures, the evening concluded. However, one of the members, who happened to be the chair of the DDO offered to give the members a tour of the main telescope used in most observations. Most members, including me, took advantage of that opportunity.

The telescope became operational on May 31, 1935, and was the second-largest telescope operating in the world at that time. This telescope was used by many renown astronomers throughout the years to study deep space objects. In 1971, most notably, the DDO was able to confirm that the Cygnus x-1 binary system has a black hole. In 2007, the University of Toronto intended to close the telescope down. However, in 2009, RASC put forward a proposal to run the telescope for educational purposes. As a result, in July 2009, it was reopened for public use by RASC and has since remained like that.

In the observatory, we saw the giant telescope that was used to observe the stars. It has a Schmidt-Cassegrain design, with a primary mirror concentrating the light to a secondary mirror and then reflecting it to the instrumentation.

Telescope used at DDO.

Telescope used at DDO.

Telescope used at David Dunlap Observatory

Secondary Mirror of Telescope.

Every time the telescope operators want to use the telescope they need to manually remove the covers of the mirrors.

The chair showed us how its mount works. It is an equatorial mount that follows the Celestial Equatorial Coordinate System, which slews the telescope based on Right Ascension (RA) and Declination (Dec) coordinates. (Think of it like Latitude and Longitude of the stars) Believe it or not, the mount is not computerized, and relies on a manual switch, and it also includes a hand crank for turning the telescope on its RA axis. It’s quite fascinating.

In addition, he showed us the spectrometer used in the telescope as well as the telescope very large 100 mm eyepiece. It gives the telescope 330x magnification, which is pretty good. It was quite a sight.

We then saw the electrical system of the telescope. It is quite old, since it still uses DC currents. One notable feature of the electrical system is a light bulb. It is notable because it is used to prevent the electrical system from freezing in these frigid Canadian temperatures. It is also worth nothing that the light bulb is still active after 60 years of use. It’s very intriguing. In addition, we learn that the dome rotation was powered not by gears but by a pulley system balanced with 10 stones (140 lbs) of weight. I say 10 stones because the weights were made in the UK.

In the other side, we saw the equipment used to recoat the primary mirror. Every two years, the aluminum coating on the mirror is recoated to maintain its reflective properties. The process they use is the same process used when it became operational. First, the operators use a manual elevator to bring the two ton mirror to the ground level. Before that, the bottom of the elevator needed an additional two tons attached to balanced the elevator. Once the mirror is at ground level, they use sodium hydroxide to clean the aluminum off, using diapers to wipe it down. It was quite astonishing.

Once the mirror is completely clean, they put the mirror in a vacuum chamber. Attached in the upper rim of the chamber are evenly-spaced diodes. Each diode requires three slivers of aluminum on it to coat the mirror. Once the aluminum is in, and the mirror is in place, they vacuum seal the chamber. In a specific sequence, they activate each diode which evaporates the aluminum and evenly applies the aluminum across the entire mirror. Once it has dried for a day, they take the mirror and place it back into the telescope. The secondary mirror goes through a similar process inside a smaller vacuum chamber.

Fun Fact: The primary mirror was so big that they had to bring it inside using an unfinished opening in the wall. It would not fit through the doors.

After that, our tour ended and we all went back home.

Overall, the event was a great success. I learned a lot of new interesting and informative facts about the universe around me. Closer to home, I learned the history of the DDO, how the DDO’s main telescope works, and what it takes to maintain it over the years.

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February Astronomical Events

Hello everybody,

Here are the astronomical events occurring in the month of February: (All times are given in UTC format.)

  • This February there will be no new moon. Here is the reason why:
    • The new moon was on January 30, 2014 at 21:38 UTC.
    • The moon drifts along the Celestial Sphere (CS) at a rate of 52 min/day, which results in a sidereal month (The time it takes the Moon orbit the Earth) of 27.3 days.
    • The sun drifts along the CS at 4 min/day.
    • When comparing the Moon’s drift with respect to the sun’s drift, the Moon drifts at a rate of 48 min/day. As a result, it has a synodic month (The time it takes to repeat the same phase) of 29.5 days.
    • This means that the next full moon will take place 29.5 days after January 30, which lands on March 1, 2014 at 8:00 UTC.
    • This last happened in 1995, and won’t happen again until 2033.
    • In addition, this can only happen on February’s due to the month being shorter than the Moon’s Synodic period.
  • February 6: A Double-transit event that will occur from 10:20 – 12:44 UTC. The best place to view it is from Western North America.
  • February 14: The Full moon will take place. The moon will reach its full phase at 23:53 UTC.
  • February 21: The Moon will occult Saturn at approximately 22:18 UTC. This will be visible from the Indian Ocean.
  • February 26: The Wanning Crescent Moon will occult Venus at approximately 5:23 UTC. This event is best viewed in Central Africa.

If you have any questions, please let me know on:

This month I will post some articles about our planet Earth. Stay Tuned!