About daytime day… I was about to say päivä is the hours most people are awake, but that discriminates against shift workers. Then I thought about saying it’s the hours during which you have daylight, but that discriminates against North Finland beyond the Arctic Circle, where you have several days or weeks with no sunrise in winter. It’s generally understood as both, even by shiftworkers and the Sami.

(Yes, my comment is a bit late with respect to the original publishing date. I found this blog entry through a link in 9 Nov, 2011 entry about Carl Sagan’s birthday.)

I’ve been learning about this in my astronomy course but didn’t really get it until I read this. Thanks again.

Intresting note :In the 1800s the devations in Mercurys orbit were thought to be caused by the gravational pull of a planet closer to the sun then Mercury.One Astronomer claimed to have discoverd it and named it Vulcan (no not Mr Spocks homeplanet) other Astronomers could not confrim his discovery and soon the idea of planet Vulcan was abandon .But there are a few who still look for it, the last serious attemp was useing Skylabs telescope with negative results .One Astronomer has sugested there may be an Asteroid belt between Mercury and the Sun but no one has as yet found it.

“One astronomer eh?” Another astronomer who is pretty familiar here has also written about this topic too several times incl. quite recently – see :

http://blogs.discovermagazine.com/badastronomy/2010/12/03/inside-mercurys-orbit/

for more.

Wonder if he could kindly give us a progress update on the Vulcanoid search? Please BA?

@Messier Tidy Upper (47) is it not ‘par ardua’ for difficulties ‘per aspera’ to aspire.
As in ‘Par ardua ad mona’ through troubles to the Isle of Man the motto of the Isle of Man TT races.

Could be, I’m just quoting it as I remember seeing it. Which was Isaac Asimov quoting it in one of his short stories written decades ago so, yeah, it may not be exactly right.

I’d check the book again – fairly sure I got it right from there – but unfortunately all my books are packed into boxes and inaccessible for the next week or so. (Painting & carpeting happening at my house presently.)

By that line of reasoning, though, the moon is much more vital to modern science then Mercury, as Eddington’s measurement of the bending of starlight by the Sun’s gravity during a total eclipse in 1919 was what really put general relativity on solid evidential footing.

For item 2, there are 2 different lunar effects. The Earth and Moon are orbiting their common center of gravity, several thousand miles from the center of the Earth (well inside the mantle.) While the Moon is revolving around the CoG in a big ellipse once a month, the Earth is also revolving in a much smaller ellipse about the same point, but on the opposite side. The 2nd lunar effect is the tides, which I think amount to several inches of twice daily vertical travel even if you are standing on solid rock. (If you’re in a boat on the Bay of Fundy, you would be moving up and down 10 meters or more twice a day.) Also, don’t forget solar tides, which are about half the size of lunar tides!

Perhaps the BA refers to different versions of Latin (e.g. ancient versus mediaevel Latin perhaps?). I also understood stella to be the latin for star, as in the mediaevel song Salva Nos, thus:

Salva nos, stella maris,
Et regina celorum.

Save us, star of the sea
And queen of heaven.

Nice reference there – never heard of that one. Thanks.

I was more thinking of the way ‘stellar’ is used to pertain to stars generally, Stellar nucleosynthesis, stellar associations, stellar performances ( ), etc ..

Also from other historical Tycho Brahe’s 1573 book ‘De nova stella’ on the supernova bearing his name (SN 1572) the previous year.

Source : http://en.wikipedia.org/wiki/Tycho_Brahe#The_1572_supernova

Or Johannes Hevelius 1662 book Historiola Mirae Stellae naming Omicron Ceti “Mira” (meaning “wonderful” or “astonishing,” in Latin) and suchlike.

Source : http://en.wikipedia.org/wiki/Mira#Observation_history

As for ‘astra’ the first example of that that springs to mind is the latin saying quoted by Isaac Asimov :

Per aspera ad astra – Through difficulties to the stars!

Source : ‘Trends’ short story in The Early Asimov (one of 3 volumes, pretty sure that was the title – books currently unavailable for citing other details.)

Oh and in the word Astr(a)-onomy too!

I’d love to see the question of the precise meanings & differences between stella, astra & sidus resolved if anyone’s got enough latin knowledge to enlighten us please!

@#37 : Sorry, still not working. Not sure why but I can’t seem to get that link to go where I want it – afraid you’ll just have to scroll down to comment 27 there.

o_O

This sounds like utter nonsense to me, and fairly easily debunkable nonsense, too.

Agreed, but we need to find out more about what the person meant. Maybe they meant the element mercury as it is used in electronics?

Does the planet Mercury influence our radio waves and cell phone communications?
The first person I met this year was a master’s student at a New York City university (Columbia) who told me that without Mercury we could not have our cell phone communications.

He even told me that his Professor thinks astrology is nonsense, but this has not changed the student’s mind.

Specifically what can anyone tell me about the planet Mercury affecting our cell phone technology?
Is it a myth spread by astrologers desperate to justify their ancient and unscientific beliefs?

This sounds like utter nonsense to me, and fairly easily debunkable nonsense, too.

First off, if Mercury influenced cellphone communications (or any other form of radio communication), you should be able to use the behaviour of your cellphone to predict the location of Mercury. Challenge this “master’s student” to do this, and see what (s)he says.

Second, there is pretty much no way that Mercury can electromagnetically influence anything happening here on Earth.

Let’s look at the numbers. A typical cellphone has a maximum rf (radiofrequency) output power of 5 W. (Normally, your phone will emit less than this to conserve the battery, but if the base-station signal is weak the cellphone increases its output power when trying to connect to it.) Base-stations emit higher power (they have mains electricity), and I don’t know exactly how much they use, but let’s say, for the sake of argument, that it’s 50 W (in reality, I expect it to be less than this because, if this were the case, the base station would become an “alligator” – all mouth and no ears).

Generally, you need to be within 20 miles of the base station for your phone to be able to connect to it. In reality, you are often much closer than this, even if you have a poor signal, due to local topography, interference from buildings and other nearby dialectric materials and so on. But let’s call it 20 miles for the sake of argument (this is probably the maximum range of a typical phone and base-station combination under ideal conditions).

Next, I’m going to consider both Mercury and the base station to be point sources, from the point of view of the cellphone, to keep things simple.

The cellphone has an omni-directional antenna, so emits its power equally in all directions. Since radio waves dissipate according to a 1/r2 law, the distance matters. A lot. I’m not going to get into field-strength calcs here (‘cos I’d have to look it up to make sure I get it right), so we’ll consider the relative distances. Let’s say the cellphone is only just working well enough to make a phone call when it is 20 miles from the base station.

How far away is Mercury at this point? Well, let’s assume, for the sake of argument, that Mercury and Earth are as close as they get (i.e. are both on the same side of the sun) in their respective orbits (and, again, for the sake of simplicity, I’m going to assume circular orbits).

Earth’s orbital radius is 149,600,000 km, while Mercury’s is 57,910,000 km (from nineplanets.org). So, the distance between them is 91,690,000 km, or just over 57,300,000 miles.

Thus, Mercury is 2,865,000 times farther from the base station than is your cellphone. Thus, any rf signal from Mercury arriving at the base station would be 8,208,225,000,000 times weaker than a comparable signal arriving from your phone. Or, to put it the other way around, Mercury would need to emit a signal with an ERP (effective radiated power) of over 41 TeraWatts to have the same signal strength arriving at the base station as the signal from your phone.

The most powerful radio transmitters I am aware of are only 0.5 MW (the BBC World Service long-wave transmitters), and that’s enough power to give reception around the whole world. And it requires some pretty damn serious amplifiers. I daresay there are systems with higher output powers than this, but probably not by more than an order of magnitude. Of course, antennas can focus the fed power into a narrow beam and increase the ERP in one specific direction. A decent-sized dish antenna can provide a gain of about 50 – 60 dB (5 – 6 orders of magnitude) in ERP over fed power. So an ERP of up to 100 GW is (at least theoretically) feasible with technology that exists.

But, hey, don’t you think we might notice a flipping great big dish antenna on Mercury, now that we have high-res photos from a space probe? And, come to think of it, if Mercury is influencing radio communications here on Earth, how the hell are we able to receive signals from the Messenger probe at all?

Let’s just use stardates and be done with it all!

Heh. Douglas Adams predicted this (sort of) when he named the widely-read newspaper in The Hitchhiker’s Guide to the Galaxy the “Sidereal Daily Mentioner”.

PS. Very minor point & I’m sure there’s an explanation but :

..sidus is the Latin word for star.

Not stella(r)?

Hmmm, you may have a point. Perhaps the BA refers to different versions of Latin (e.g. ancient versus mediaevel Latin perhaps?). I also understood stella to be the latin for star, as in the mediaevel song Salva Nos, thus:

Salva nos, stella maris,
Et regina celorum.

Save us, star of the sea
And queen of heaven.

an amazing animation of this problem. (also see the “day on earth” video by the same person, for the other half of the problem)

D’oh! Wrong link :

http://blogs.discovermagazine.com/badastronomy/2010/12/27/another-exoplanet-joins-the-hr-8799-family/#comment-349772

Should be the right one now – comment 27 on that “another exoplanet for HR 8799″ thread. Not sure what happened there, sorry.

And your commenters ain’t bad either.