Monet's two versions of "The House Seen from the Rose Garden" show the same scene as seen through his left (normal) and right eyes.
The eye’s lens is pretty good at blocking ultra-violet light, so when Claude Monet (whose works we visited earlier this year) had the lens of his eye removed he could see a little into the ultra-violet wavelengths of light.
The images taken by the Hubble Space Telescope are in black and white, but each image only captures a certain wavelength (color) of light.
The Guardian has an excellent video that explains how the images from the Hubble Space Telescope are created.
Each image from most research telescopes only capture certain, specific colors (wavelengths of light). One camera might only capture red light, another blue, and another green. These are captured in black and white, with black indicating no light and white the full intensity of light at that wavelength. Since red, blue and green are the primary colors, they can be mixed to compose the spectacular images of stars, galaxies, and the universe that NASA puts out every day.
Three galaxies. This image is a computer composite that combines the different individual colors taken by the telescope's cameras. Image from the Hubble Space Telescope via NASA.
The process looks something like this:
How images are assembled. Note that the original images don't have to be red, blue and green. They're often other wavelengths of light, like ultra-violet and infra-red, that are not visible to the eye but are common in space. So the images that you see from NASA are not necessarily what these things would look like if you could see them with the naked eye.
SoX can do a lot more than this, so I though I’d compile what I’m using it for in a single, reference post. For the record: I’m using SoX in Terminal on a Mac.
Using SoX
To play a single note (frequency 173.5 Hz) for 5 seconds, use:
> play -n synth 5 sin 347
To save the note to a mp3 file (called note.mp3) use:
> sox -n note.mp3 synth 5 sin 347
The SoX command to play two notes with frequencies of 347 and 357 Hz is:
Two sound waves with slightly different frequencies sometimes cancel each other out (destructive interference) and sometimes add together (constructive interference) to create a sound that gets loud and quiter with a beat. The two lower sound waves (green and blue) are out of phase, and their combination (superposition) creates the third (red) wave.
Play two sound tones that are close together in frequency and the sound waves will overlap to create a kind of oscillating sound called a beat.
When you hear the beat (see below), you're hearing the alternating of the high amplitude region and the low amplitude region.
Below are two tones: separated and then mixed — listen for the beat.
Interestingly, you can sometimes hear the beat as a third tone if the frequency difference is just right. The frequency of the beat is the difference between the frequency of the two tones.
Notes
The SoX command to play two notes with frequencies of 347 and 357 Hz is:
I’ve not had much real musical training, but enough to know that I have a terrible ear for sound and can’t reproduce a note for anything. However, an informed source tells me that octaves represent the same note at different pitches.
The pitch is the frequency of the sound wave.
This "note" is a sound wave with a frequency (pitch) of 347 cycles per second (347 Hz), which has a wavelength of approximately 1 meter. It sounds like this.
If one note has twice the frequency of the other, they’re said to be one octave apart. For example, click on the image below to listen to the same note at different octaves:
Click the waves to hear the different octaves. The wavelengths of the sounds are shown (in meters).
One of my physics students is working on a project to demonstrate interference in sound waves, so I generated a few sound files with different wavelengths for her to experiment with.
A sound wave with a frequency of 347 cycles per second (347 Hz), which has a wavelength of approximately 1 meter. Waveform captured using the WaveWindow program.
Using SoX, you can generate waves by inputing the frequency you want (using the synth command). The frequency () depends on the wavelength () and speed () of the sound waves through air.
The speed of sound through the air depends on the temperature (it’s a linear relationship). Hyperphysics has a nice Speed of Sound in Air calculator, which tells me that at room temperature (about 25 ºC):
The wavelength of red light compares to the size of an E.Coli bacterium. Violet light's wavelength is even smaller.
A few of the steps along the Scale of the Universe flash app include the wavelengths of different colors of light. It’s a great way to show the show the relative sizes of these waves.
Parabolic mirrors magnify by reflecting parallel rays of incoming light onto a single point. (Adapted from Wikimedia Commons User:Nargopolis).
We’re talking about light and sound waves in physics at the moment, and NPR’s Morning Edition just had a great article on how the enormous, ultra-precise, mirrors that are used in large telescopes are made.
Astronomical observatories tend to use mirrors instead of lenses in their telescopes, largely because if you make lenses too big they tend to sag in the middle, while you can support a mirror all across the back, and because you have to make a lens perfect all the way through for it to work correctly, but only have to make one perfect surface for a parabolic mirror.
ScienceClarified has a great summary of the history of the Hubble Space telescope, that includes all the trouble NASA went through trying to fix it when they realized it was not quite perfect.
Large parabolic mirrors are used for magnification in telescopes. (Image via Wikipedia).
In addition, it’s interesting to note that you can also make a parabolic surface on a liquid by spinning it, resulting in liquid telescope mirrors .
) depends on the wavelength (
) and speed (
) of the sound waves through air.
