Astronomy

About one third of what I know about astronomy comes from Carl Sagan's "Cosmos." Another third from assorted writings by Isaac Asimov. And the last third from various sources. Alas, both Asimov and Sagan did their main works before Dark Matter and Dark Energy and Inflation and String Theory and The Higgs Bosson, and Many Other Developments and Discoveries.

While theoretical physics seems stuck somewhere between string theory and loop quantum gravity, astrophysics changes on an almost daily basis (or so it feels).

That's quite a change from a historical perspective. Consider, astronomy was a naked-eye pursuit since the time proto-humans first looked up at the sky millennia ago until Galileo invented the telescope. Now telescopes proliferate in a wide variety of flavors: optical, radio, X-ray, Gamma ray, infrared, etc, etc. Many are now based in pace (many wavelengths can't make it past the atmosphere).

For all that, ti's amazing what the ancients accomplished with little more than their eyes and brains. For one thign they identified all the planets visible to the naked eye (excpet one), tracked the course of the Sun over the sky in the course of the year, determined the equinoxes, etc. But this all can be summed up with one simple pgrase: the Julian Calendar.

Julius Caesar employed an Egyptian mathematician and astronomer, whose name escapes me, to reform the calendar. essentially that's the same calendar we employ now. It had one major flaw concerning leap days, adding one every four years without exception. In the long term this caused problems, and so a pope named Gregory made his own reform some centuries later to correct this. now leap days are not added to years ending in 00, such as 1900, except if they are evenly divisible by 400, such as the year 2000. This keeps the season from drifting. But other than that the anncients knew astronomy well enough to set down firm basis for a useful calendar.

More to come.

Re Julius Caesar and the calender, I believe you mean Augustus Caesar

you were right. Maybe the name should have been a hint for me [g]

Augustus did mess with the calender, that must have been what made me get it wrong

Did people really riot and demand the return of their ten days?

Well the ancients had to!!!

Light was very limited at night, so there was a lot of time contemplating the stars. The planetae were easily discoverable because their movements in the sky were quite different than the stars that move with the season. They were mystical objects. They were very bright (except Saturn) and didn't twinkle. Mars, Jupiter and Saturn were subject to mysterious retrograde motions where they appeared to be moving backwards against the motion of the night sky. They would get brighter and dimmer as their orbits moved further away from the Earth. Venus and Mercury were subject to transits across the sun.

All of this they needed to make sense of. The seasons and equinoxes helped with agriculture and worship and helped track the years. All ancient societies that relied on agriculture tracked the movements of the sun and the seasons in order to determine the best times to plant and harvest based on trial and error over the centuries.

Planets they could not make sense of in a geocentric model. The stars, moon, and sun were completely predictable, but the planetary records were not, and it took until the 16th century for Copernicus' heliocentric theory to take hold, though it was introduced by others earlier. Up until then the planets were mystical objects and planets had meaning.

Time was quite important. For agricultural and worship purposes, people saw fortunes comes and go if they didn't pay attention to the weather and the seasons, so it made sense to track these and find a common way to track the passage of time.

Cool! What's your sign?

(j/k, j/k!)

Quote: boymimbo

Well the ancients had to!!!

So do we.

Quote:

The planetae were easily discoverable because their movements in the sky were quite different than the stars that move with the season.

true. That's how come nearly every culture figured them out. But it's not as easy as it sounds. If you don't believe me, try to figure out the planets' motions yourself.

Quote:

Planets they could not make sense of in a geocentric model.

They made some very good tries. Ptolemy's notions were outrageous and awfully complicated, but he almost made them fit. All that kept him from succeeding was reality.

Quote: Nareed

true. That's how come nearly every culture figured them out. But it's not as easy as it sounds. If you don't believe me, try to figure out the planets' motions yourself.

I often wonder if we are too dependent on the giant's shoulders we stand on. I know lots of stuff about the universe, but I have absolutely no way of proving or even knowing how to go about proving it.

Quote: FrGamble

I often wonder if we are too dependent on the giant's shoulders we stand on.

Of course we are. We wouldn't have the kind of lives we enjoy without all of them.

Quote:

I know lots of stuff about the universe, but I have absolutely no way of proving or even knowing how to go about proving it.

You don't even know how to make a pencil. I mean no slight. I don't know, either. If figuring out the planets seems hard, imagine figuring out how to feed yourself in the wild, all alone, without anyone else to help, even given what you know. You'll be begging for a Walmart or a McDonald's.

that's how much you, and everyone else, depends on the titans who came before, and on the titans who are alive and well right now and coming up with innovations, and those who actually make them, and those who grow and distribute food, etc, etc.

Pluto probe awakes

http://www.nbcnews.com/science/space/its-alive-nasas-new-horizons-pluto-probe-wakes-work-n262996

Quote: rxwine

Pluto probe awakes.

I think New Horizons is the fastest probe ever launched. I think, too, it's the only probe conceived while its target's discoverer, Clyde Tombaugh, was still alive.

It's certainly the first probe launched towards a planet which won't reach a planet when it gets to where it's going.

Hopefully it will 1) reach another Kuiper Belt object and 2) follow up on the Voyagers readings on the boundaries of the Solar System.