Tag Archives: Earth

Leap Year Explained Simply

It’s Leap Day today, and that means people born on February 29th finally get to have a birthday. But why do we have Leap Years? What’s the purpose? Well, it ensures that our seasons don’t drift.

You see, it takes the Earth 365.256363004 days to orbit the sun (this is known as the sidereal year). The calendar year is 365 days. But every 4 years, we have an extra day. So, we add a day to the years that can be divided by 4. This year is 2016, and is divisible by 4.

Sounds simple, doesn’t it? But it gets a bit complicated.  This accounts for 365.25 days. But what about the extra 0.006363004 days? This accumulates, and after 400 years, it equals about 3 days extra. So, we have 3 too many Leap Days every 400 years. So what do we do? We just drop the Leap Days that happen on century years, but keep the ones that can be divided by 400. As a result, the year 2000 was a Leap Year, but 1900 and 2100 are not.

Leap years fall on years that can be divided by 4, except if they can be divided by 100 (not including the ones that can be divided by 400). This balances the calendar and seasons, and we don’t have any drift.

But why is it called Leap Year? Well, in normal years, let’s say that March  31st is a Monday, then the next year it’s a Tuesday, and then it’s a Wednesday the following year. But then, on a Leap Year, we leap over the next day (Thursday) so it’s on a Friday. And that is why we call it a Leap Year.

Any questions?

Top Ten Largest Moons

This is the newest series to come to I Read Encyclopedias for Fun, the weekly Top Ten. I will be publishing top ten lists of various topics scientific, geographic, and anything related to books, TV shows, and movies. They are not merely lists, however. They also include some interesting information. Some of the lists will be purely factual, while others will be my opinion. So, let’s get started.

Top Ten Largest Moons

10. Oberon

Voyager_2_picture_of_OberonWith a mean radius of 761.4 km, Uranus’ moon Oberon is the tenth largest moon in the Solar System. It has a mass of (3.014±0.075)×1021 kg , and a mean density of 1.63±0.05 g/cm³. It’s the second largest moon of Uranus, and was discovered by William Herschel in 1787. It’s estimated to be about 50% water ice, and differentiated into a rocky core and icy mantle. The surface is slightly reddish and is covered with craters and chasmata. It has only been visited once, by Voyager 2, which mapped 40% of its surface.

9. Rhea

PIA07763_Rhea_full_globe5With a mean radius of 763.8 km, Rhea is the ninth largest satellite in the Solar System. It has a mass of (2.306518±0.000353)×1021 kg, and a mean density of 1.236±0.005 g/cm³. It’s the second largest moon of Saturn, and was discovered by Giovanni Domenico Cassini in 1672. Due to its low density, it’s estimated to be about 75% water ice, and only about 25% rock. It appears it has a homogeneous interior, meaning there is no core. It is heavily cratered and has only a few chasmata or fractures on the trailing hemisphere. It’s been extensively photographed and mapped by the Cassini orbiter currently at Saturn.

8. Titania

Titania_(moon)_color_croppedWith a mean radius of 788.4±0.6 km, Titania is the eighth largest moon in the Solar System, and Uranus’ largest. It has a mass of (3.527±0.09)×1021 kg, and a mean density of 1.711±0.005 g/cm³. It was discovered by William Herschel in 1787. It’s estimated to be around 50% water ice, and may have a rocky core. The surface is cratered fairly heavily, but not as much as other large Uranian moons, meaning it has a younger surface. It features several large chasmata and scarps, pointing towards tectonic activities in its past. It may have a tenuous carbon dioxide atmosphere. About 40% of the surface has been photographed by Voyager 2.

7. Triton

480px-Triton_moon_mosaic_Voyager_2_(large)With a mean radius of 1353.4±0.9 km, Triton is the seventh largest moon in the Solar System, and Neptune’s largest. It has a mass of 2.14×1022 kg, and a mean density of 2.061 g/cm3. it was discovered by William Lassell in 1846. Triton is unique in that it’s the only large moon that orbits its planet in a retrograde direction. Because of this, the tidal forces from Neptune will cause its orbit to degrade and crash into the planet or create a new ring system in about 3.6 billion years. Triton is also very active geologically. It has several nitrogen geysers that have been observed to be erupting. The surface is relatively young, having been resurfaced in the past, leaving it smoother and more reflective. It’s likely to be differentiated, having a core, mantle, and crust. It’s guessed it may have a liquid water ocean beneath the surface. The core likely generates heat to help keep the water liquid. The atmosphere is a thin nitrogen atmosphere, and clouds have been observed. It’s theorised that Triton is a captured moon, likely a Kuiper Belt object.

6. Europa

Europa-moonWith a mean radius of 1560.8±0.5 km, Europa is the sixth largest moon, and the fourth largest of Jupiter’s Galilean satellites. It has a mass of (4.799844±0.000013)×1022 kg and a mean density of 3.013±0.005 g/cm3. It was discovered by Galileo Galilei in 1610. Europa is one of the most exciting satellites in the Solar System for one major reason, it has a large subsurface ocean of liquid water. It’s so large that it has more water than Earth. Because of tidal heating, it is quite possible that it has hydrothermal vents, which are teeming with life in Earth’s oceans. The surface is incredibly smooth and made of water ice. It has features similar to the Arctic polar ice cap and very few craters. The surface is young and constantly being resurfaced. Beneath about 10-30 km of ice, there’s a thick ocean of liquid water, around 100 km thick. And then beneath that is a rocky interior and a metallic core. One of the most prominent features is the lineae, or the extensive lines that cover the surface. These are cracks where fresh water may be coming to the surface, and plates of icy crust move against each other.

5. Moon

LRO_WAC_Nearside_MosaicWith a mean radius of 1737.1 km, the Earth’s Moon is the fifth largest moon in the Solar System. Its mass is 7.342×1022 kg and mean density is 3.344 g/cm3. It’s the second densest moon in the Solar System. It’s the most familiar moon, as we can see it very easily from Earth. Its discovery is prehistoric, since we’ve always known it’s there. The surface is heavily cratered, except in the Maria, which are basins flooded with lava. There are also volcanoes, some of which are relatively young. This suggests a warmer interior than previously thought. The interior is differentiated, with distinct crust, mantle, and core. The surface is dominated by silica, alumina, lime, and iron oxide. It’s tidally locked, so we only see one side of the Moon. The far side is very different, lacking the maria we see on the near side. It’s also the only moon that has been landed on by humans, and one of only two moons that has been landed on by robotic probes.

4. Io

Io_highest_resolution_true_colorWith a mean radius of 1821.6±0.5 km, Io is the fourth largest satellite, and the third largest of Jupiter’s Galilean satellites. It has a mass of (8.931938±0.000018)×1022 kg and a mean density of 3.528±0.006 g/cm3. It is the most dense natural satellite in the solar system, and is also the most geologically active. It has more than 400 active volcanoes, which makes it the most active object in the Solar System, more than Earth. It was discovered by Galileo Galilei in 1610. When Io was first viewed up close, it was a surprise. The surface is a very colourful mixture of red, orange, yellow, white, and black. Several volcanoes can be erupting at the same time, and lava lakes have been observed. The surface composition is mostly silicates, sulfur, and sulfur dioxide. Due to tidal interactions with Jupiter, the interior is constantly being flexed. With an internal structure more similar to terrestrial planets than other moons, it has almost no water ice. It has a crust, mantle, and hot core.

3. Callisto

CallistoWith a mean radius of 2410.3±1.5 km, we’re moving into the top three, and the true heavyweights of the Solar System’s moons. It’s the third largest in the Solar System, and the second largest of Jupiter’s moons. It has a mass of (1.075938±0.000137)×1023 kg and a mean density of 1.8344±0.0034 g/cm3. With a relatively low density, it is about half ice and half rock. It was discovered by Galileo Galilei in 1610. The outermost Galilean satellite, it has far less tidal influence from Jupiter, and therefore has an old, relatively inactive surface. It is covered by craters, and is considered the oldest surface in the Solar System. Unlike other large moons, it’s not very differentiated, and is mostly a mixture of rock and ice covered by a possible liquid water ocean and an icy crust. It has a thin carbon dioxide atmosphere.

2. Titan

Titan_in_true_colorWith a mean radius of 2575.5±2.0 km, Titan is the second largest moon in the Solar System, and Saturn’s largest. It’s even larger than Mercury, but has a smaller mass. It has a mass of (1.3452±0.0002)×1023 kg and a mean density of 1.8798±0.0044 g/cm3. It was discovered by Christiaan Huygens in 1655. It is the only satellite outside the Earth-Moon system that has been landed on by a space probe, the Huygens lander. It has a very thick atmosphere, thicker than Earth’s and with a 45% higher air pressure at the surface than Earth’s. The composition is mostly nitrogen with some methane and hydrogen. What makes Titan incredibly interesting is the surface. It is very Earth-like, with mountains, rivers, and lakes. However, the lakes are not water, but liquid hydrocarbons, mainly ethane and methane. There are some craters, but the surface appears to be quite young, with possible cryovolcanism. Basically, the surface is like Earth’s but ice replaces rock and hydrocarbons replace water. It’s a differentiated body with a silicate core, an ice layer, then a possible liquid water ocean, and the ice crust.

1. Ganymede

Ganymede_g1_true-edit1With a mean radius of 2634.1±0.3 km, Ganymede is the largest moon in the Solar System, and Jupiter’s largest. It has a mass of 1.4819×1023 kg and a mean density of 1.936 g/cm3. It was discovered by Galileo Galilei in 1610. The surface is quite complex with older cratered regions and a younger grooved terrain. It’s mainly water ice with some carbon dioxide and sulfur dioxide. Some salts hint at a salty ocean beneath the surface. It’s fully differentiated with a hot iron-nickel core and silicate mantle. It’s believed there’s a thick liquid water ocean between two layers of ice. There’s an extremely tenuous oxygen atmosphere. Ganymede has its own magnetic field, and has even been observed to have aurorae. This also helps strengthen the theory that there’s a salty ocean. Tidal stresses from Jupiter aid in heating the interior, which makes Ganymede another possible candidate for life.

If you have any questions about these or any other moons of the Solar System, I’ll do my best to answer them. As this was one of my biggest interests in university, I’ve been paying attention to news related to the Solar System and its moons. Ask your questions or leave comments in the comments section below.

Real and Fictional Geography Preview

As I mentioned before, I’ll be working on Geography Quick Facts and the Ariadne Encyclopedia’s country profiles at the same time. So, here’s a comparison between Earth and Ariadne.


Number of countries (official): 193

Total land area: 148,326,000 square kilometres

Largest country: Russia (17,075,200 square kilometres)

Smallest country: Vatican City (0.44 square kilometres)

Number of continents: 7 (Asia, Europe, Africa, North America, South America, Australia/Oceania, Antarctica)

Number of oceans: 5 (Pacific, Atlantic, Indian, Arctic, Southern)


Number of countries (official): 249

Total land area: 150,930,246 square kilometres

Largest country: Name to be revealed (3,336,638 square kilometres)

Smallest country: Name to be revealed (630 square kilometres)

Number of continents: 4 (Ipeiros, Voreios, Tropikos, Notos)

Number of oceans: 4 (Tethys, Thetis, Proteus, Nereus)

As you can see, the land area is surprisingly similar. I didn’t plan it this way, it just turned out like that after measuring the land area of each country. There are also fewer continents and oceans on Ariadne, though its largest continent, Ipeiros, is huge. At 103,001,817 square kilometres, it’s larger than Asia’s 44.58 million square kilometres, and Eurasia’s 54.76 million square kilometres. It’s a supercontinent!

As I go through each country on each planet, you’ll get to discover many more stats, facts, and information that should be interesting. What are you interested in finding out?

Real and Fictional Geography

I think it’s about time I get started on this. I’m going to be showing you both real and fictional geography at the same time. What does that mean?

First of all, I’ll be working on Geography Quick Facts, going through each country in the world alphabetically, providing you with various facts and figures about each country. I won’t be going into depth about culture, the people, or history of the countries, but I’ll be focusing more on statistics, such as population, largest cities, and tallest mountains, as well as physical characteristics, such as bordering countries, climate zones, and geological zones. I will provide pictures whenever possible.

As for fictional geography, I’m going to do something similar for Ariadne. But these will be the start of the country profiles for the Ariadne Encyclopedia. As I haven’t published anything yet, I’ll only focus on the physical geography of the countries. You can see the names of them, but you won’t get to learn about the cultures, history, or any demographics. Only physical geography, including climate, geology, and ecology. These profiles will grow over time, as I write the books, and I can flesh out the countries, including minor spoilers (these will be marked as spoilers, so you can skip over them).

So, which one are you interested in seeing?

Ever Watch the Moon Pass In Front of the Earth? Incredible

I saw this earlier. This animation is from several still images of the moon passing in front of the Earth. The images were taken from the DISCOVR spacecraft about 1.6 million km away from the Earth. It’s a quick video, so it won’t take much of your time.

I don’t think there’s ever been a video or set of images like this before.

Just a note about the moon. You may notice that the leading edge is green. This is not because it’s a photoshopped fake. It’s because they take three images in different colours: red, blue, and green.  The green image just happened to be the last one taken, and the moon had already moved a bit, so that’s why it has a green fringe on the leading edge. There’s an argument on Facebook about this, and some people are claiming it’s a conspiracy. Those people just don’t understand how images are made from spacecraft. They don’t just take a colour photo, they take three monochrome photos at three different wavelengths that correspond to red, blue, and green. Then they combine the images to give a true colour image. Since there is a thirty second delay between the three images, this green offset is the result.

Anyway, incredible set of images!

Fantasy Novel Settings Based on the Real World

A lot of fantasy authors are influenced by real history and locations. Some come out and say that they are a part of Earth’s lost history, and some are Earth’s future. And it seems like many are based on the European Middle Ages.

Lord of the Rings is based on Europe, and I think Tolkien admitted that. I believe it’s supposed to be Europe, but long before recorded history.

A Song of Ice and Fire (or Game of Thrones) is also based on Europe, but not actually in Europe, but a fictional world. In fact, the entire war is inspired by the War of the Roses.

Shannara is quite different, though. It’s based in a world that had gone through an apocalypse. I’m not exactly sure of the precise location, but it is North America.

What are some other Earth-based fantasy novels and series?

Influence of Climate Change on My Writing

Climate change is a big topic these days, especially since it was announced that we crossed over a fourth limit for Earth’s habitability, which makes the future look pretty bleak.

Although you may not see it, Journey to Ariadne actually has a lot of influence from climate change.  At the moment, the web serial is focusing on the people and what they are doing and thinking while preparing to go to another planet.  They don’t live on Earth, so the effects of climate change are not felt by them.  However, things are a mess on Earth.  What you see in the web serial will be adapted into a novel, but there will be a lot more focus on what’s happening on Earth.  You’ll get to see the other side and hopefully understand what effect climate change has on the environment.  It’s not pretty.

There are many things to consider when writing about it.  The temperature is likely to be warmer, but with wild hot and cold swings in summer and winter.  There will be extreme storms.  The sea levels will be up with many major coastal cities flooded and abandoned.  The amount of forests will have decreased, as will the arable land, so less food.  That means lots of starvation and a smaller population.  Pollution isn’t likely to be a problem, as alternative eco-friendly energy sources would be in use, but the damage was already done in the 20th and 21st centuries.  Deserts are likely to be bigger, as well.  Another problem is access to clean freshwater.  This can lead to conflict.  With a lot of people trying to leave areas that are not very habitable, refugees are a problem.  There’s going to be a lot of fighting.  Due to the lack of oil, oil-rich countries of the 20th and 21st centuries will either have to rely on other industries or find themselves in the company of developing nations.

So, it’s definitely not a very nice place to live 150 years in the future.  This will be the basis for the other half of Journey to Ariadne.  I’m only showing you some of the Mars side of things.

Honestly, Earth is Tiny

Ever wonder how Earth compares in size with Jupiter?  How about the Sun?  I found this article with some pretty good pictures showing just how big the Earth is.

Not impressive enough?  Well, how does it compare with stars?  You know, the Sun isn’t that big when compared to the biggest stars in the galaxy.  This video illustrates that perfectly.

Impressed?  Discuss below.