Is there anything of longer wavelength than radiowaves?
It looks like radiowaves start at 10^5 Hz.
Is there any form of EM rad at 10^0 - 10^4 Hz?
Thanks.
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Is there anything of longer wavelength than radiowaves?
It looks like radiowaves start at 10^5 Hz.
Is there any form of EM rad at 10^0 - 10^4 Hz?
Thanks.
Order of Kilopi
If you look here, you can see that there are things with longer wavelengths than radio waves, such as ELF and VLF.Originally Posted by TOEfetish
As above, so below
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ULF, ELF and VLF are called radio waves too, just like LF, HF, UHF, SHF and so on. They are just ITU wavelength bands. Anything down to 0 would be called a radio wave as far as I know. You see some really long wavelength radio sources associates with plasmas IIRC.If you look here, you can see that there are things with longer wavelengths than radio waves, such as ELF and VLF.
Order of Kilopi
Perhaps we should ask if there are frequencies that have wavelengths larger than the universe.
Et tu BAUT? Quantum mutatus ab illo.
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If elf and vlf electromagnetic radiation, emitted from a very distant location, say 10billion lightyears away, arrives here on Earth,
it would have redshifted due to universe expansion,
What would this emr look like when it finally gets here?
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Like EM with a very large wavelength.
Redshifting would cause minimal elongation of the waves between the source and us. If this wasn't so, distant galaxies should be red, which of course they're not.
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Red shifting doesn't necessarily make things red--but wouldn't they be elongated by the amount of the Hubble constant?
But what do you mean by "EM with a very large wavelength" and "minimal elongation of the waves", those phrases seem to contradict each other?
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I think he or she is saying that there wouldnt be that much of an observable redshift from the hubble constant. I disagree.
Moderator
If you already have an answer, why post the question? What is your answer?
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Right, which is a negligible effect on what we call visible light. It's not obviously red--the spectrum is shifted so finely toward the red that instrumentation is needed to see it.
The same should hold true for radio that has large wavelengths.
Minimal elongation from the baseline: the wavelength that was emitted at the radio source.
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Tell that to the Cosmic Microwave Background Radiation.Right, which is a negligible effect on what we call visible light. It's not obviously red--the spectrum is shifted so finely toward the red that instrumentation is needed to see it.
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I dont already have an answer. I was trying to help you understand what SkepticJ was saying.
I still do not know what the longest known radio waves would look like when they get stretched out.
I was saying that i disagree that the observed redshift would be negligible - in fact i was agreeing with you...it would redshift in the amount of the Hubble constant.
Order of Kilopi
Longer radio waves.
Order of Kilopi
My bold. That depends on how much redshift and the type of spectrum. If we had a source with a blackbody spectrum like that of Sirius, and put it at a distance where z =3, the wavelengths will be stretched by a factor of 4 across the board, and the source will look more like an M star, which is noticeably redder that the bluish white tint of Sirius. In practice, even whole galaxies that far away are so faint that we probably would not see anything but shades of gray with our own eyes, even with the largest telescopes.
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If you put Sirius at z=3, you won't see anything at visible wavelengths; the blackbody peak is in the blue-green, so stretching that by a factor of four is going to put everything in the IR. At z=1, it will look something like an M star. Still, I agree with your point that redshift can be very noticeable and obvious.
Order of Kilopi
At z=1 Sirius would be about 2.5 giga parsecs away or about a billion times farther away than it is, making its intensity about 1/31600th of what we see, which is I'm not completely mistaken would make it a magnitude twelve thousand star (approximately).
This is not something we're going to actually observe for individual stars.
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Reductionist and proud of it.
Being ignorant is not so much a shame, as being unwilling to learn. Benjamin Franklin
Chase after the truth like all hell and you'll free yourself, even though you never touch its coat tails. Clarence Darrow
A person who won't read has no advantage over one who can't read. Mark Twain
Order of Kilopi
No such radiation can arrive here on Earth, period.
IIRC, ELF is used for (one-way) communication with submarines, and there is a need for only one transmitter. Why? Because the ionosphere is a perfect mirror for this EMR (electromagnetic radiation), and the ground/sea a near-perfect one too. That also means no ELF from beyond the ionosphere can reach us, "here on Earth".
And why is the ionosphere opaque to ELF? Because it's a plasma, with an electron density sufficiently high that EMR with ELF frequencies is fully absorbed. Check out the term "plasma frequency" for more details, e.g. from here.
What about above the ionosphere? Well, the stuff within the Earth's magnetosphere is also a plasma, as is the interplanetary medium, the interstellar medium, the intergalactic medium, the ... Of course, each has a different plasma frequency (because their electron densities are different) - so the frequency of EMR at which they are opaque will also differ - but I think, if you plug in the numbers, you'll see that ELF cannot go anywhere, and that any EMR which is redshifted to the ELF will also be stopped dead in its tracks.
Would you like to do some sums, TOEfetish, and work out with the minimum EMR frequency is, for us to be able to observe a distant source emitting it, say from an observatory in Tasmania, or on the Moon? Or one on a small moon of Pluto? Or on some Oort cloud object, well beyond the heliosheath?
What colour hair would I have if my maternal grandfather had died before he met my maternal grandmother?What would this emr look like when it finally gets here?
Sometimes a question just does not make sense.
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It's even worse than Nereid suggests - the ionized components of the galactic interstellar medium absorb radiation with frequencies less than ~3 Mhz, with this absorption reaching a factor >1000 by 100 kHz. This paper has a data plot including measurements from the Radio Astronomy Explorer B in lunar orbit as well as distant probes in solar orbit (both to get beyond interference from the Earth's auroral zones). The observer would have to be outside the Galaxy to pick up much of this radiation (and it would have been attenuated greatly on the way out of most galaxies as well).
Established Member
That's true that we don't observe individual stars like this, but 1/30000th brightness is only a difference of ~12-13 magnitudes at worst (every five magnitudes is a factor of 100 in apparent brightness). If you put Sirius a billion times further away than it is, the apparent brightness goes down by a factor of 10^18 (distance squared), which is still about 40 magnitudes difference, not 12,000. However, that is still enough to make it completely invisible (Hubble's LM is ~30).
Order of Kilopi
I blame writing this at work, I did a square root where I should have squared, then divided instead of log'ed.
Still invisible though, so I didn't screw that one up.
__________________________________________________
Reductionist and proud of it.
Being ignorant is not so much a shame, as being unwilling to learn. Benjamin Franklin
Chase after the truth like all hell and you'll free yourself, even though you never touch its coat tails. Clarence Darrow
A person who won't read has no advantage over one who can't read. Mark Twain
Order of Kilopi
I never intended to imply the possibility of observing a single star like Sirius at such vast distances. This was a thought exercise with something as luminous as a large galaxy, but having a spectrum like that of a 10,000K blackbody. At z = 3 it would look like a 2,500K blackbody, which is some 95% infrared but still glows brightly like a tungsten filament during a brownout.
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