Microwave Ovens Posing as Astronomical Objects | Hacker News Reader

Microwave Ovens Posing as Astronomical Objects

spectrum.ieee.org

58 pointsjonbaer29 comments

This is embarrassing to the observatories involved. If you go to the National Radio Astronomy Observatory in the US, one of the first things they show you is a microwave oven inside of a stainless steel sealed box. It is there so people can heat their lunch without interfering with the observatory. They also have a small display where you can place your digital camera, cell phone, etc. and look at its emissions across the spectrum.

They encourage visitors but you really have to leave everything electronic behind. The staff uses old diesel vehicles without electronics. Any on site radio communications is done on a frequency below the cutoff of the observatory.

You'd think they could install a gas stove.

Does flame give off EM emissions?

Edit: Radio emissions, I mean. Of course we can see it :)

Office break-rooms usually only have microwave ovens, not stoves because fire safety regulations are more stringent for an area in a commercial building which is designated as a "kitchen" which a stove usually makes it.

You'd want one with a pilot light, not the now omnipresent electronic/spark ignition.

I am neither a chemist nor a physicist, but I do not believe that burning natural gas gives off anything that would foul their readings.

It's possible that there are exotic combustible materials that could do this, however.

> The astronomers were flummoxed—that is, until one of the testers, during a third attempt, opened the door of a microwave oven before the magnetron was shut off by the timer. They found that although the door shuts the magnetron off, a whiff of gigahertz radiation could escape.

I assume it is miniscule level that escapes - there is no 'lock' feature on any microwave I've seen, forcing power off before door opening - but in the future I'm going to leave a microwave a rest for a second before opening the door.

Pretty sure your cellphone and wifi hotspot are more dangerous microwave sources than that :)

Considering they lasted "a few milliseconds", I would not be too concerned.

I'm not too concerned because it is microwave radiation, but a few milliseconds is more than enough for lethal doses of radiation.

It is not ionizing radiation, the primary hazard of microwave radiation is its heating effects on sensitive tissue that has poor blood circulation -- in particular it has been implicated in the development of cataracts in the eye. So to a first approximation, the few milliseconds of 1000W output is really only as hazardous as a few minutes of the typical leakage you get with the door closed (somewhere on the order of 5 mW).

No, it's full power, for the full duration that it takes for the door to swing from fully closed to engaging the switch that kills the microwave.

But exposure to a fraction of a second of microwaves is not dangerous, to the best of my knowledge. It just annoys astronomers and keeps microwave designers up at night.

By the time the door opens any appreciable amount, the microwaves will have long dissipated. It's a very short burst, so even though it's at full (and decaying) power, the total energy released is harmless.

I still would recommend stopping before opening, if only to avoid accidentally triggering the redundant failsafe switch which shorts out the power and blows the fuse.

I still would recommend stopping before opening, if only to avoid accidentally triggering the redundant failsafe switch which shorts out the power and blows the fuse.

Could you elaborate further on the design of this failsafe and what, specifically, triggers it? Do all microwave ovens have it?

It's a triply-redundant design, present in practically all ovens:

http://www.microtechfactoryservice.com/switch.html

This is tangential, but if you have an old microwave that you don't mind perhaps getting a bit dirty, you can make ball lightning in the comfort of your own home. Discovered this during my "I wonder what will happen to this when I microwave it!" phase.

1) Take a tealight. Bog standard little candle.

2) Remove the metal casing. Snip the little metal foot off the bottom end of the wick. You now have a little puck of paraffin with a wick in it.

3) Place said candle in a glass tealight holder. Ikea sell 'em for a few pence.

4) Light it. Stick it in the microwave, right in the centre, without the turntable.

5) Engage. Observe with wonder as the paraffin vapour enters a plasma state and hovers in the middle of your microwave, contained by the microwaves.

I dare say this works better in some than others, and perhaps depends on the shape of the standing wave in your microwave, and I make no guarantees as to your or your microwave's safety - but it's a really neat demo, either way.

If you try this, put a glass of water inside the microwave with the candle. You don't want the microwave to run empty, and the water will keep that from happening.

As I said, old microwave you don't care about. Glass of water would likely absorb most of the energy that would otherwise be gleefully wasted on making plasma.

Even easier is to turn half a grape to plasma in a microwave: https://www.youtube.com/watch?v=0i2lhO3bSjQ

Using a high-temperature-resistant glass sphere with an opening on one end can protect the roof of the microwave oven if it doesn't have a standing wave that would keep the plasma localized. Most glass probably can't withstand prolonged heating from the plasma, so don't run it for long.

Microwave ovens can and often do leak quite a bit of radiation during operation. If you want proof, set up your wireless router near the microwave, turn the microwave on and watch as your wireless signal just vanishes.

We were talking about this yesterday in my astronomy department and one of the professors here told a similar story about some radio interference at the Green Bank telescope. The astronomers there had noticed that for some time there had been a small burst of radio interference every day right around 5pm, plus or minus about 5 minutes.

One of the employees at the observatory is a guy who drives around and talks to the locals to try to track down any sources of interference that the telescope is detecting. He went around asking people if they were using their microwaves, cell phones, wifi, etc., and none of them were. He eventually went to one lady's house and happened to be there right around 5pm. He was asking the usual questions and she said she hadn't been using her microwave, etc., but then she said, "Oh, could you hold on a moment? I have to feed my cat." And then she put a can of cat food in an automatic can opener. That turned out to be the source of the interference.

I just heard this story second-hand, so I can't vouch for the accuracy of all the details, but it seems plausible enough to me.

Seems plausible to me too .. they use antique diesel trucks on-site because they don't have spark plugs or onboard computers:

http://www.autoblog.com/2014/04/24/national-radio-astronomy-...

Isn't there an intelligence listening post near the observatory that would also be affected by EMI?

So basically if someone with an undergrad in EE decided he hates astronomers the way Ted Bundy hated women, he could screw up that field of science for the next few centuries with no one being the wiser for it?

Yes, but you can do that about everything.

He could probably set back research a bit while researchers figure out what he's doing, but not that long. Also, unless he's operating from right near one of these radio astronomy observatories, he would likely be violating FCC or similar regulations in doing this and would face legal action against him once sufficient evidence had been collected.

In case your interested in the back story of how this was 'discovered', I posted earlier the original article interviewing the PHD student who discovered the phenomenon - https://news.ycombinator.com/item?id=9490371

I'm guessing quick transients are the issue here?

Long-lived ones can be ruled out by looking for some characteristic strength curve as the antenna (earth) sweeps across the sky onto and off of the presumed source. A terrestrial source, including satellites and planes, would have a different curve. SETI has software to filter on this.

Reply on news.ycombinator.com