Lunar Eclipse of April 4, 2015

Even though we just had a total solar eclipse on March 20th, just two weeks later, there will be a lunar eclipse. In fact, most of the western hemisphere will be able to witness at least part of this eclipse on April 4, 2015.


Remember that eclipse seasons happen every six months and always have a solar eclipse and lunar eclipse two weeks apart. The alignment of the Sun, Earth, and Moon will always determine which one occurs first. However, there are sometimes when the alignments are right, there may be three - a solar eclipse sandwiched between two lunar eclipses. However, this eclipse season there are only the two this year.


From before, we learned that a lunar eclipse will happen during a full moon. The Earth will be between the Moon and the Sun and the shadow of our planet will fall on the Moon, obscuring it. This eclipse will begin at 9:01 UTC. If the Moon is out during this time for you, you will be able to see the eclipse occur.

Year-long Mission in Space

Today, astronaut Scott Kelly and cosmonaut Mikhail Kornienko will launch from Baikonur in the Ukraine to begin a year-long mission in space on board the International Space Station. The unique thing about Scott Kelly is the mission will allow us to look at how extended time in space can affect the human body as Scott Kelly has a twin brother, retired astronaut Mark Kelly.


The science we will learn from this is remarkable because it will give us an understanding of how the human body will react to extended time in space, and give us knowledge of how to alleviate problems on the body for longer duration flights, for example, to Mars.


Follow Scott Kelly on twitter here.
Follow Mark Kelly on twitter here.
Follow the International Space Station here.


Watch the launch live here.

Update on Pluto

A while back, I posted an argument about why Pluto is not a planet. Recently, there has been a movement to reinstate Pluto as one of the planets in our solar system. Let's delve into this a bit further.


From the previous post, here are the IAU definitions of a planet and a dwarf planet.

• A planet is a spherical body that orbits the Sun and has cleared its orbit of other objects, i.e. it does not share an orbit with other bodies (not including moons).
• A dwarf planet is a spherical body that orbits the Sun but has not cleared its orbit of other objects. They may co-orbit with other bodies. Many of the Trans-Neptunian Objects, Kuiper Belt Bodies, Oort Cloud comets may have the same semi-major axis as other objects, therefore are not planets.

As to these current definitions, we can see that Pluto is not a planet. All the arguments I made are in the previously linked post. A nice thing about science is that new information can change our understanding of nature and the universe. Science is a fluid subject. Our perceptions can alter. So that is why it may be important to reinvestigate the idea of a planet.


If we were to redefine what makes a planet, we should be clear on what is and what is not a planet. Pluto is smaller than seven moons in our solar system, including our Moon. However, Mercury is also smaller than the two largest moons, Ganymede (orbiting Jupiter) and Titan (orbiting Saturn). We can all agree that Ganymede, Titan, the three other Galilean satellites, Triton (orbiting Neptune), and our Moon are NOT planet, they are moons. They orbit around planets which in turn orbit around the Sun. Pluto, only orbits the Sun (though it can be argued that it also orbits around the common center of mass of its system (Pluto, Charon, and its other orbital companions).


If the IAU does change the definition of a planet, it will have to get rid of the idea of co-orbiting bodies that are a significant fraction of the largest body's mass and radius. Remember, Charon is about 11.6% the mass of Pluto and has a radius about half that of Pluto. Our Moon is only 1.2% the mass of Earth and has a radius just over a quarter of the Earth. Looking at all the large satellites of the gas giant planets shows that all of them are significantly smaller in comparison to their parent planet than our Moon is to the Earth.


So if the definition is changed, what other objects in our solar system will have to be redesignated as a planet? Pluto is obviously the first. Eris will also have to redefined as it is a larger body than Pluto. After that, it depends on what the lower limit the IAU wants to use. Makemake may become a planet, Ceres may as well, though if Ceres does get redefined, than all the trans-Neptunian objects larger than Ceres will have to be classified as planets. Not only that, we will have to add a third type of planetary body along with terrestrial and Jovian. This will have to be something in between, though that type is not really a bridge between terrestrial and Jovian.


At the moment, I personally like the definition we have for planets. It's clear, concise, and makes a lot of sense. But as I said before, science can change and our understanding of what is going on can help us make more informed conclusions. Only if the IAU changes the definition of a planet, only then will Pluto, Eris, and some of the other dwarf planets/minor planets in our solar system become full-fledged planets.


We will learn more about Pluto once New Horizons reaches the Plutonian system in July of 2015. Then we will know more about Pluto and its sisters and may be able to make more informed conclusions about what they are.

Gravitational Coupling Constant

Much like there is a coupling constant for the electromagnetic force (also called the fine structure constant), there is one for the gravitational force, called, believe it or not, the gravitational coupling constant. It is used to define the gravitational attraction between two elementary particles having some mass.


The way it is defined is as the gravity between two electrons and is a unitless quantity.

Where:

• G is the gravitation constant  (6.67x10^-11 m³/s²kg)
• m_e is the mass of an electron (9.109x10^-31 kg)
• ℏ is the Planck constant over 2π (called the reduce Planck constant, 1.05457x10^-34 J*s)
• c is the speed of light (3x108 m/s)

Compare this to the fine coupling constant which is approximately 1/137 and we can see that the electromagnetic force is 10⁴³ times stronger than the gravitational force for electrons. Depending on what elementary particles are used (proton-electron or proton-proton), the ratio between them can vary, but in all cases, the electromagnetic coupling constant is magnitudes greater than that for gravity. In Martin Rees' case, he compares the fine structure constant to the gravitational coupling constant for two protons, and the ratio is 10³⁶. Any variance of this ratio can lead to the universe not being the way we see it.


To calculate the gravitational coupling constant for two protons, replace m_e with m_p in the top equation. To calculate it for the attraction between a proton and an electron, replace one m_e with m_p.    

Seasons on Earth

Recently, everyone on Earth went from one season to the next. In the northern hemisphere, we went from winter to spring and in the southern hemisphere, summer gave way to the fall (autumn). How exactly are the seasons defined?


Just this past Friday, the northern hemisphere experienced the vernal equinox, while in the southern hemisphere, the autumnal equinox occurred. We already know why they call these the equinoxes as they were explained in the previous posts. However, why does the northern hemisphere experience one season, while the southern hemisphere experiences the opposite (spring-fall and summer-winter)? It all has to do with the Earth's axial tilt.


The Earth rotates on its axis once a day. Most everyone knows that. However, the rotational axis of the Earth is tilted with respect to its orbital axis by about 23.5º.

So what does this mean?


When one half of the Earth is tilted towards the Sun, that half will receive more direct sunlight. The other half will not. It is like when you take a flashlight and aim it at a wall. If you keep the flashlight parallel to the wall, the light circle is tight and compact, if you tilt the flashlight away from the wall, the light circle becomes elongated. The same amount of light is hitting the wall, but in a larger area.

 

Another interesting thing about the seasons is that the time of year they occur change over time. However, none of us will be alive when January will be summertime in the northern hemisphere. This will occur in about 13,000 years. If you can wait until 28,500 CE (common era, formerly known as AD), April will be the middle of summer for the northern hemisphere. This is because the Earth wobbles on its axis, causing precession of the equinoxes (which in turn, also causes the solstices to precess). Currently, the summer solstice occurs when the Sun is in the constellation Gemini, but will someday be in the constellation Sagittarius.

 

The Vernal Equinox

On March 20th, 2015, the northern hemisphere's spring season officially began. This time of year is called the vernal equinox, or spring equinox. We've discussed equinox before and we learned that equinox comes from the Latin for "equal night". It just means that there are the same number of hours when the Sun is above the horizon (day) as there are when the Sun is below (night).

We have discussed the autumnal equinox before, and we learned that this is when the Sun appears to travel from north to south along the ecliptic across the celestial equator. In this case, the vernal equinox occurs when the Sun travels across the celestial equator from south to north along the ecliptic. You should note that when the spring starts in the northern hemisphere, fall or autumn begins in the southern hemisphere.

Another fun thing to note is that on either equinox, the Sun rises due east and sets due west. At the equator, the Sun is directly overhead at noon. As the Sun travels farther north on the ecliptic and we get deeper into the northern spring, the Sun will be farther north in the sky at noon until it reaches its farthest point north at the summer solstice (which will be discussed as we approach that time of year).

The Fine Structure Constant

The fine structure constant, also known as the coupling constant for electromagnetism, is used to define the strength of the electromagnetic force between two charged particles. It is symbolized by α and is approximately 7.2974e-3 (or approximated as 1/137) and is unitless.


In terms of other physical constants, in this case the elementary charge e, the Planck constant h, the speed of light c, the permittivity of free space (electric constant) ε_o, and the permeability of free space (magnetic constant) μ_o, we can relate α to these quantities.

The amazing thing about the fine structure constant is that any change in one of the fundamental constants will change α. A change of just 4% of the constant will not allow carbon to form, and hence no carbon-based life. An even larger change to α > 0.1 would mean that stellar fusion can't take place and therefore no warm planets, no liquid water, and again no life.


Fun note: the product of the permittivity of free space ε_o and the permeability of free space μ_o is the reciprocal of the speed of light squared.

The Anthropic Principle

There has always been a question about why our universe is the way it is. Physics tells us that the laws of physics and the constants we measure are perfect for life to exist. If any laws were slightly different or any constants were a little smaller or larger than what they are, we would not be here to question any of this. This idea is called the Anthropic Principle and in a way, it's a circular argument. The universe is the way it is because we are here and we are here because the universe is the way it is.


Because we are here, we are able to question what makes the universe unique to allow stars, galaxies, planets, and life itself to form. Martin Rees surmised that there are six fundamental numbers that dominate the cosmos to allow the universe we see to exist. We will go over these six numbers in the following posts, but the numbers can be broken down into a variety of the four fundamental forces: the strong nuclear force, the weak nuclear force, the electromagnetic force, and the gravitational force.

1. The strong nuclear force is the force that hold the nucleus of an atom together. Without it, nuclei would not be stable because nuclei are made up of protons, which are all positively charged. This is the strongest of the four forces, but acts on the smallest scale.
2. The weak nuclear force is the force responsible for nuclear decay, the decay of subatomic particles (like the proton and neutron) and fission of atoms.
3. The electromagnetic force is the force responsible for the electron orbiting the nucleus of an atom, the existence of electromagnetic radiation, even the force between magnets.
4. The gravitational force is the force that interacts between masses. It is what keeps our feet on the surface of the Earth and what allows bodies to orbit one another. In terms of size, it is actually the weakest of the four forces, but acts on the highest scales. Because it is weaker than the electromagnetic force, it is the reason why electrons orbit the nucleus, rather than falling into the nucleus.

The six numbers that Martin Rees surmised control the cosmos are:

1. The ratio between the fine structure constant (electromagnetism) and gravitational coupling constant
2. The fraction of the mass of four protons to one helium nucleus
3. The mass density ratio
4. The energy density ratio
5. The energy required to break up the largest structures in the universe
6. The number of spatial dimensions

We will talk more about these as we continue.

Solar Eclipse of 20 March 2015

There is a solar eclipse this week that will be visible in a small portion of the world. So for my readers in Europe and northwest Asia, you will get to see a partial eclipse. If you live in the archipelago of Svalbard, you will be able to see the total eclipse.

All information below is from Time and Date.com

Area seeing the total solar eclipse.

More than 90% of the sun is covered.

Up to 90% of the sun is covered.

Up to 40% of the sun is covered.

Eclipse is not visible at all.

Note: Percentage values (%) relate to moon coverage of the sun and depends on location. Visibility is weather permitting.

Here are the times the eclipse will be visible.

Event	UTC Time
First location to see partial eclipse begin	Mar 20 at 7:41 AM
First location to see full Eclipse begin	Mar 20 at 9:09 AM
Maximum Eclipse	Mar 20 at 9:45 AM
Last location to see full Eclipse end	Mar 20 at 10:22 AM
Last location to see partial Eclipse end	Mar 20 at 11:50 AM

Olbers' Paradox

In the early 1800's, there was a quandary. Scientists did not know about the size of the universe or the speed of light. There was an assumption that the universe was infinite in size, age, and mass. Not only that, they assumed that light itself travelled instantaneously from place to place. They did not know about the Big Bang, or Hubble's Law, or even Relativity. So from these assumptions, there arose a question: why is the night sky dark?


They believed the universe was infinite and static. Because of this, they wondered where all the stars were. Imagine looking in any direction in the sky. If the universe is infinitely populated with stars, no matter where you look, you will see a star, despite the great distances involved (remember, light is instantaneous). Therefore, you should see light from that star. Because of this, at night, when the Sun is not dominating the sky, the sky itself should be lit up like daytime. Though this question has been posed before, Heinrich Olbers was the first to formulate the question and try to answer it, and we call this question, Olbers' Paradox.






He came up with a few reasons why the night sky is not dark. I'm only going to mention two for simplicity.

1. The universe is not infinite. There is a limit to the size as well as the age of the universe, though the size may be larger than the age of the universe. We still don't know exactly how big the universe really is since we can only see about 14 billion light-years in any direction.
2. The speed of light is not infinite. He didn't know how fast it was, but he could conclude that light travelled at a finite speed. Therefore, light from stars that are farther away from us than the age of the universe have not had enough time to reach us since the star/galaxy/whatever was formed.

From these two reasons, we can see the night sky is dark because the light from most of the stars in the universe has not had enough time since the light left the star to reach us.

Cosmological Constant

When Albert Einstein applied his equations of General Relativity to the observable universe, he found something that he didn't like. His equations were correct, but for some reason, his equations predicted that the universe was dynamic when he and everyone else though the universe was static. This was in 1917, before the Big Bang theory and before Edwin Hubble found that the universe was expanding. To account for what he felt was incorrect, he introduced a fudge factor to take away the dynamic universe solution. He called his fudge factor, the cosmological constant. He hoped and felt that in time, physics and astronomy would be able to allow the cosmological constant to go away. When Hubble found the expansion of the universe and the Big Bang theory were proposed, Einstein thought that his cosmological constant was his biggest blunder. But was it?


Now, with the introduction of dark energy to help explain the expansion of the universe, the cosmological constant was reintroduced. As explained last time, if the dark energy density is constant, the universe will be open and expand forever. With a constant dark energy density, this implies that the universe is homogeneous in both space and time. Remember that this is referred to the Perfect Cosmological Principle which was briefly mentioned here. In other words, the universe appears static and therefore, the cosmological constant may be a physical quantity describing the dark energy density of the universe. Unfortunately, we still don't know what the dark energy density is doing and it may be centuries or millennia before we know.

Dark Energy

What is dark energy?


First, what isn't dark energy? It isn't energy used by either Sauron or Lord Voldemort. They use dark magic, which isn't the same. You also shouldn't confuse it with negative energy, which is strange phenomena in itself. We will look at negative energy later.

Dark energy is defined as the energy that permeates space and drives the expansion of the universe. At the present time, the amount of dark energy in the universe is seeming to accelerate the expansion rate of the universe. It should be noted, however, that this does not mean that the universe is open. Just because the universe's rate of expansion is accelerating now, it does not mean that sometime in the future, the rate of expansion can slow, stop, or reverse.


Dark energy is thought to be one of two things: a constant energy density over time and space (static) or a scalar field density that has a value that can change with time or space (dynamic).


If the energy density is constant over time and space, that means as the universe expands, the amount of energy (not including mass) must increase. The only way this happens without violating the conservation of energy is that mass must be converted to energy in some way. This could be done in the normal way (matter-antimatter collisions) or in some way that we don't know. This constant energy density is referred to as the Cosmological Constant, and was first introduced by Albert Einstein. We will discuss this more later. If this is what dark energy is, then we live in an open universe.


The other is that dark energy density is a changing quantity which in the future could either slow down (but not stop - open universe), stop (flat universe), or reverse (closed universe) the expansion, depending on how the density changes over time.


At our current knowledge, dark energy is 68.3% of the total mass-energy density, dark matter is 26.8%, and ordinary matter is only 4.5%. So you can see, what we don't know about the universe is a heck of a lot more than what we do know.