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Thread: Episode 16: Across the Electromagnetic Spectrum

  1. #1
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    Post Episode 16: Across the Electromagnetic Spectrum

    We see the Universe in visible light with our photon detecting eyes. We can feel infrared heat with our photon detecting hands, and we get sunburns with our ultraviolet photon detecting skin (ouch). ...

    Read the full blog entry

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    It was mentioned quite a few times during the show, but what exactly is 'Red Shift'? can you please explain.

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    Redshift happens when an object emitting light is moving away from an observer. The frequency of the light is lengthened to longer and longer wavelengths. In visible light, colours are shifted to the longer, or more red end of the spectrum.

    Here's a good explanation from Wikipedia
    http://en.wikipedia.org/wiki/Redshift

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    OK I now understand, so I take it that as the Universe is expanding the objects we observe are 'red shifting', but are there any objects which are 'blue shifting' i.e. coming towards us!

  5. #5
    Wouldn't the Andromeda galaxy be blue-shifted since we're on a collision course? I wouldn't know by how much, but I would suspect it's happening.

    Clair

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    There are a few objects that are blue shifted. Andromeda is one of them.

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    What are the maximum or minimum wavelengths for electromagnetic waves?
    Is there a need or any reason for any such limitation?
    The answer to this question, I think, would have some pretty far reaching implications.

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    Post Why Infrared? Why not Radio Waves?

    Quote Originally Posted by Fraser View Post
    We see the Universe in visible light with our photon detecting eyes. We can feel infrared heat with our photon detecting hands, and we get sunburns with our ultraviolet photon detecting skin (ouch). ...

    Read the full blog entry
    In the last show based on 'electromagnetism' I learnt that we can look deeper into the dust through the infrared light. It is so because it has a longer wavelength than the visible light and thus it is scattered less. If that's the reason why can't we use Radio light (for objects emmiting radiation in the radio region) to peer more deeper into clouds of dust and gas, as Radio waves have more longer wavelength! If we use the Radio wave, do scientists have plans to place out a radio telescope in space just as they are going to place the James Webb Space Telescope in 2011.

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    Quote Originally Posted by Himanshu Raj View Post
    In the last show based on 'electromagnetism' I learnt that we can look deeper into the dust through the infrared light. It is so because it has a longer wavelength than the visible light and thus it is scattered less. If that's the reason why can't we use Radio light (for objects emmiting radiation in the radio region) to peer more deeper into clouds of dust and gas, as Radio waves have more longer wavelength! If we use the Radio wave, do scientists have plans to place out a radio telescope in space just as they are going to place the James Webb Space Telescope in 2011.
    the object or area being observed must be giving off radio waves to be detected by a radio telescope. since all matter gives off infrared light it is a very useful tool for measuring inside dust and gas clouds, but radio waves are more rare as an emission from matter.
    we could theoretically send radio waves and wait for them to bounce back, but because of the long wavelength and incredible distance this method would be effective for only the closest bodies in space (think of waiting 4 years each way for radio waves to travel to and reflect back from the nearest star, creating a waiting peiod of 8 years for the first results, and that's only if the waves even reflect back, rather than passing right through the distant object).
    Last edited by luckynate; 2007-Jan-03 at 12:42 AM.

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    Speed of light and size of the Universe

    I was facinated by what Dr. Gay said when she said: objects 4.7{whatever} MegaParsecs appear to be moving at .23c because the space between us is expanding. She then said that hypothetical objects 13.99 billion light-years away would seem to be moving away from us at >1c.

    Question: could the Universe be larger than 13.77 Billion YRs, but we cannot see objects so far away beacuse the photons from such objects would never be able to "catch-up" with us?

  11. #11
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    Quote Originally Posted by RUF View Post
    I was facinated by what Dr. Gay said when she said: objects 4.7{whatever} MegaParsecs appear to be moving at .23c because the space between us is expanding. She then said that hypothetical objects 13.99 billion light-years away would seem to be moving away from us at >1c.

    Question: could the Universe be larger than 13.77 Billion YRs, but we cannot see objects so far away beacuse the photons from such objects would never be able to "catch-up" with us?
    wouldn't this effect be cancelled by the inability of waves/particles to move apart faster than the speed of light(C), and instead result in a gradual increase in matter/energy density further away from the observer (approaching infinite) kinda like an inside-out black hole just inside the 'relative' boundary of the universe and creating an infinite curve at the edge of relativity.

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    Just nit-picking here, but the snakes that Pamela described in the show that are able to see into the infrared part of the spectrum don't actually use their eyes to accomplish this. Pamela is refering to pit vipers, which are a family of snake species that have organs located in these funky little pits in their heads that pick up the heat emitted by nearby prey. Their eyes, as far as I understand, only see in the visible spectrum just like us humans.

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    well bees can see ultraviolet with their eyes

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    I just subscribed yesterday and realized that Dr. Pamela Gay was a voice of the past for me, I went to McDonald Observatory one summer with her and ASA many years ago. I am still a huge fan of astronomy, although now an accountant, and would like to ask a question about the moon broadcast. It was mentioned that Saturn could lose it's rings and Mars could possibly gain rings. How could this happen and why? Pamela, you are doing great, it was such a breath of fresh air to hear your voice after so many years.
    Lauren

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    I wish this podcast had happened three months ago--I totally bombed my chem test on the electromagnetic spectrum because my teacher didn't explain it very well. A nicely clarifying podcast...

  16. #16
    Thanks for a clear and fact filled podcast.

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    I was thinking about this episode, and Fraser asked a question close to, "How can I see the objects in the room with visible light when they aren't 5000 degrees?" and Pamela said, "The light from the light bulb..." which I interpreted to mean, the light from the light bulb is 5000 degrees, which gives off visible light, which bounces off the objects in the room, which absorb some of the wavelength (meaning, some colors of the spectrum) and what's remaining reflects to my eye to identify its color. Is that right? Is the interior of a lightbulb really 5000 degrees? Is the glass of the bulb not melted because of the vacuum inside? Why doesn't a light bulb work outside of a vacuum? (Oops, straying away from astronomy with that last one...better ask the guy at Home Depot.)

    Also, with visible spectrum being what it is, why do I see the color brown? Or gray? What is not being absorbed to reveal those dark murky colors to me, and why don't I see those colors in a rainbow?

    Thanks!

  18. #18
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    I'd really like a transcript for this one.

    Any chance of it happening soon?

    Thanks!

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    It's coming, we're working back through the older episodes.

  20. #20
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    Great. I love the info, but I'm more of a visual learner.

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