Looks like it's time for another short break. I haven't posted in nearly a week and don't anticipate being able to post much over the next three, which are the last two weeks of classes and one of finals. I had intended on writing something over Thanksgiving, but was pretty backlogged with work (two homework assignments and one test to grade) so I didn't even get a chance to finish my own homework.
I may get a chance to post a few times in the next three weeks, but I doubt I'll be able to add anything to my Scientific Misconceptions series. On that topic, the next post will be entitled "It's only a theory!" and will basically address the scientific process and clarify the terms we use (such as the difference between a theory and a hypothesis).
If you'd like to see anything specifically addressed, leave a comment or send a message.
There is a new Symphony of Science video online! This one features Carl Sagan, Richard Dawkins, Michio Kaku, and Robert Jastrow, and is just as fantastic as the first two. MP3 downloads are available at the Symphony of Science website.
We must ask ourselves We who are so proud of our accomplishments What is our place in the cosmic perspective of life?
The Leonid meteor shower will reach its peak tonight at 5 pm EDT when Earth passes through the densest part of the debris stream left by Comet Tempel-Tuttle.
Comet Tempel-Tuttle passes close to the Sun every 33 years, leaving a trail of meteoroids (objects 10-6 to 10 m across), which Earth encounters every November. It has been 11 years since Tempel-Tuttle last made its appearance in the inner Solar System.
A meteor is a meteoroid that has entered Earth's atmosphere (it gets called a meteorite if is survives its trip all the way to the ground). This meteor shower gets its name from the constellation Leo, which is in the portion of the sky where the meteors appear to originate. Predictions for this year's even vary considerably, from NASA's 20-30 per hour in the US and 200-300 per hour in Asia to estimates of 500 per hour at its maximum.
To see this meteor shower, simply look up for a few minutes! If possible, get to a sparsely populated area--light pollution can be a great annoyance for observing. Luckily, we will have a new Moon, so its reflected light won't interfere at all. Though the map below may look like bad news for those of us on the East Coast, there are still dark skies to be found. Just download one of the high-resolution maps linked at the bottom of the page and find a dark location near you.
When polled, "What causes Earth's seasons?", a large percentage of the people asked would respond that it is our varying distance from the Sun. While Earth does go between 147 million kilometers away at its closest point and 152 million kilometers away at its farthest point, this is not a significant variation. In fact, the northern hemisphere is experiencing summer when the Earth is at its farthest point from the Sun.
This misconception often comes from over-exaggerated diagrams of Earth's orbit, showing it as an elongated ellipse:
Earth's orbit, if viewed from above, would appear circular. The amount that Earth's orbit deviates from circular, called eccentricity, is very small--so small that we can't perceive the difference.
But what does cause the seasons?
The seasons are due to the fact that Earth's spin axis (also called the axis of rotation) is tilted 23.5 degrees to the ecliptic. The Earth orbits the Sun in a plane--think of a flat sheet of paper with Earth's orbit traced out on it, and the Sun drawn in very near the center of the orbit. This plane is called the ecliptic. If the Earth were to have no tilt at all, its spin axis would point straight up out of our plane, perpendicular to the ecliptic. Our tilt is measured in relation to this perpendicular.
Our planet's tilt affects how much sunlight different portions of the globe get at different times of the year. The first day of spring and fall is referred to as an equinox (from Latin, equal + night) because the day and night both have the exact same length at all points on the globe. The Sun's rays are hitting the equator from directly overheard.
The first day of summer and winter is referred to as a solstice and is respectively the longest and the shortest day of the year.
So why should this cause a difference in temperature? The answer involves simple geometry. Sunlight coming from directly overhead has to heat a smaller area than the same amount of sunlight hitting the surface of the Earth indirectly (at an angle). The surface receiving direct sunlight heats up more than the surface receiving indirect sunlight, making it warmer. The surface receiving indirect sunlight is relatively cooler.
direct sunlight (left) compared to indirect sunlight (right)
The idea of seasons caused by varying distance is in no way far-fetched, though. Mars, which has some Earth-like characteristics, with a 24.6 hour day and a 25.2 degree tilt, also has a far more eccentric orbit--about 8 times as eccentric as Earth's orbit! Instead of our small variation of 5 million km between closest and farthest point, Mars has a variation of almost 60 million km. This large difference is far more important to Mars' season than its tilt.
Since I grade an astronomy class for non-majors, I've come across a lot of common scientific misconceptions. I've had an interest in teaching science to the general public for a while now, so I'm going to make this into a series, written whenever I have both the time and a good topic in mind.
The very FIRST misconception I'd like to clear up is the idea that science is hard. A lot of the time, when I tell someone that I am studying astrophysics, I get a response like, "Wow, you must be really smart!" It's not a matter of being smart; it's a matter of love for the subject. There is honestly nothing I would rather do than contemplate supernova explosions.
Anyone is capable of learning science; we just need to change the mindset given to children early in their education. We need to stop saying things like, "Oh, you must not be much of a math person". It's true that math or science will not come naturally to everyone, but that doesn't mean that it can't be taught and that definitely doesn't mean it shouldn't be emphasized.
Redshift
Light travels in waves, and not all of it is visible to the human eye. In fact, the portion of the electromagnetic spectrum that is visible to the human eye is actually quite small.
The frequencies toward the red side of the spectrum are less energetic (lower energy), while the frequencies toward the blue side of the spectrum are more energetic (higher energy). Believe it or not, our own Sun emits all wavelengths of light, but with different intensities; we see sunlight as "yellow" because most of the light emitted falls into that range.
"Shifting" occurs when an object that emits light is moving toward or away from us. This works in the exact same way as Doppler shift does for a siren on a firetruck. As the truck approaches, it will sound like it has a higher pitch than it would if you were standing beside a non-moving firetruck. After it passes and drives away, the siren will sound like it has a lower pitch. This is because the sound waves get compressed as it gets nearer and stretched out as it recedes.
The same thing happens with light. When a star is moving away from us, the light waves we receive get stretched out. In the diagram above, you can see that the more "stretched" looking waves are toward the left of the image. This is redshift. The opposite is true for a star moving toward us; the light waves get compressed, which corresponds to the right of the image. This is blueshift.
They derive their names from the fact that red light is a longer wavelength of visible light and blue is a shorter wavelength of visible light.
redshifted spectral lines of a distant star (right) in comparison to our own Sun (left) (source)
Have a science question? Ask me in the comments, send me a message, or email me (jupiter312@gmail.com)!
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