Faster-Than-Light Travel

Since humanity first went into space, we've always wondered if there is a way for us to travel to the distant stars faster than the light from those stars reach us. Faster than light travel has been a mystery to us and something we want to figure out if we ever want to go beyond our own Solar System.

What is faster-than-light travel? Basically, it going faster than the speed of light which is 300,000 km/s or 671 million miles per hour. At that speed, we could reach Jupiter from Earth in a little under an hour. Neptune, at 2.795 billion miles from the Sun, could be reached in about 4 hours, the flight time from New York to Dallas. To reach the closest star, Proxima Centauri, would still take 4.22 years. Knowing this, is it possible we could achieve faster-light-travel?

Probably not because when we think of faster-than-light travel, we think of traveling through normal space using the known laws of physics. The one theory that will control whether or not we can travel faster than light is special relativity. This is Einstein's theory that describes the physics at travels at or near the speed of light. Hendrik Lorentz found that as the speed of an object increases, so does it mass. At low speeds, i.e. speeds we achieve on Earth, this increase in mass is negligible. However, at near light speeds, the mass increases so much that when an object travels at the speed of light, its mass becomes infinite. This is given by

where γ is the Lorentz factor given by:

As you can see, as the velocity increase, the Lorentz factor decreases, until at v = c (the speed of light), γ = 0. And anything divided by 0 is infinite. So, sorry, we will never be able to travel through normal space at velocities greater than the speed of light.

So what about science fiction? They show spacecraft travelling faster than the speed of light, right? Well, technically, no. They have apparent faster than light velocity. What this means is that they follow laws of physics about which we do not know much. These laws that could, theoretically, allow apparent faster than light travel. I'm going to focus on two: warp drive in Star Trek and hyperdrive in Star Wars.

Warp drive describes exactly what it does: it warps space. A warp drive in a Star Trek ship creates a "warp bubble" around the ship allowing space in front of the ship to be compressed and the space behind it to be expanded. This allows the ship seemingly to travel faster than light.

via http://physics.stackexchange.com/questions/13444/getting-back-out-of-an-alcubierre-warp-bubble

This is called a Alcubierre drive, which is essentially a warp drive.

Star Wars, however, uses something a little more exotic. It uses something called hyperdrive, which is essentially creating a wormhole in space to allow the ship to travel across vast distances via a shortcut in hyperspace. Think of it as taking a piece of paper and folding it in half so that the two ends are about an inch apart. If an ant wanted to travel from a point on the top half of the sheet to a point on the bottom half of the sheet, it would have to travel the whole length of the sheet. Now, imagine that that ant could create a hole in the top half and a hole in the bottom half and is able to link those two holes together. The ant has created a wormhole allowing it to travel much faster between points than taking the conventional way.

via Space.com

These two methods of faster-than-light travel may someday be achieved. But the physics and engineering of how to accomplish them are not well understood, and for that which we understand, it requires a form of energy that we do not have the ability to create at this time. Both methods require negative energy which may be discussed at a future time.

Ion Drives

Previously, I talked about ions. Remember, they are atoms that have either more or less electrons than protons. For ion drives, positive ions, also called cations, are used to propel the craft ahead.

The ions are created in a chamber where the electrons are stripped from an atom or molecule (many times xenon or ammonia, depending on the thruster type), then are accelerated via an electrostatic or an electromagnetic field.

Ion drives have a very high specific impulse, which means they are very efficient engines. Specific impulse is the ratio between the spacecraft's thrust (the force at which the spacecraft is being pushed along) and the weight of the fuel used to create that thrust).

However, the thrust from an ion engine is small since ions themselves are rather tiny. Ion engines are not great from getting place to place quickly in the solar system. Typically, ion drives will be used for space stations for maneuvering or for deep space probes. Though the thrust is tiny, over time, that thrust can add up to a large velocity for the spacecraft.

Deep Space 1

Via NASA

Schematic of Deep Space 1

via NASA

January

January. New Year (well, at least those of you following the Gregorian calendar). New Beginning. New blog post.

Sporadically, throughout the year, I am going to be discussing a little bit about the calendar because the calendar actually is based on astronomical phenomena. For example, the term for one-twelfth of a year is called month, which comes from the name Moon, derived for Proto-Germanic maenon. The division of the year into months comes from the lunar cycle, which is approximately 30 days.

I just want to begin this sporadic series by discussing where the name of January comes from. It is actually derived from the Roman god Ianus (no J's in Latin) who was the god of doorways and passages. He is also known as the two-headed god as he can see forward and also backwards, at the same time. Ianus is a god who can look in the past, yet still see peer ahead to the future. Good name for the month that begins a year.

Christmas Day Full Moon

Today is Christmas in the Christian world. The full moon also happens to fall on this day. A full moon occurring this time of year is called a cold moon as it is the beginning of winter in the northern hemisphere (though, right now, much of the eastern US is actually warm rather than cold).

The strange thing is that the full moon has not been on Christmas Day since 1977 and will not occur again until 2034.

Nothing else is unusual about the full moon today, but just the date it happens to fall on.

Twinkling Stars and Static Planets

Twinkle, Twinkle Little Star
How I wonder what you are.




Everyone remembers this nursery rhyme. The question is why do stars twinkle? And how come planets do not?




The short answer is that it has to do with the apparent diameter of the star and the planet. Stars are generally so far away that they have no apparent diameter, so that when light from the star enters our atmosphere, the light is easily diffracted due to different pockets of air. Since the width of the light is so small, these diffractions make it seem as if the star's light is constantly blinking in and out as the light is diffracted away from our eye as the light travels through the atmosphere.




For planets, however, they do have an apparent diameter, albeit much tinier than that of the Sun or the Moon. But this size is enough that when light from the planet travels through different pockets of air in the atmosphere, only a small portion of the light is diffracted away from our light of sight, so the brightness of the planet does not waver, and therefore does not twinkle.

Supermoon Lunar Eclipse

On September 27th, we experienced an event that does not happen very often, a supermoon lunar eclipse. We have had a supermoon before, and I've talked about it (see Supermoon). A supermoon is just the moon at perigee. However, this time, we had a supermoon occur when we had a lunar eclipse.

Lunar eclipses aren't all that rare (they happen once every six months), but to have one occur when the moon is at perigee is a sight to behold. The moon appears the largest and the lunar eclipse at this time is actually the shortest total lunar eclipse to occur. It is the shortest because the moon is at its closest, so it is actually moving at its fastest. Many lunar eclipses can last a few hours, but totality for this eclipse was only an hour and a half.

If you want to know more about lunar eclipses, see here.

Autumnal Equinox

This past September 23rd, the northern hemisphere experienced the beginning of our fall season.

In terms of astronomy, what does this mean?

In the sky, if we could see the ecliptic, the path the Sun travels on as it appears to cross the sky, the point of the autumnal equinox occurs when the Sun crosses the celestial equator as it travels south on the ecliptic. This marks the beginning of autumn for all of us in the northern hemisphere, and the beginning of the spring for those in the southern hemisphere.

Another way to look at it, is that the Sun is directly overhead at the equator, which means that the Earth itself is tilted in the plane perpendicular to the Sun. Neither the northern hemisphere or the southern hemisphere is tilted towards the Sun. But at this point, the southern hemisphere will begin to receive more sunlight as the southern hemisphere is beginning to be tilted more towards the Sun.