Theoretically, in a typical dark sky, the dark adapted human eye would see the about 5,600 stars brighter than while in perfect dark sky conditions about 45,000 stars. In practice, the atmospheric extinction and dust reduces this number somewhat. In the center of a city, where the naked-eye limiting magnitude due to extreme amounts of light pollution can be as few as 200 to 500 stars may be visible. Colors can be seen but this is limited by the fact that the eye uses rods instead of cones to view fainter stars.
Key moments in history: Early cultures identified celestial objects with gods and spirits. They related these objects (and their movements) to phenomena such as rain, drought, seasons, and tides. It is generally believed that the first "professional" astronomers were priests, and that their understanding of the "heavens" was seen as "divine", hence astronomy's ancient connection to what is now called astrology. Ancient structures with possibly astronomical alignments (such as Stonehenge) probably fulfilled both astronomical and religious functions.
Calendars of the world have usually been set by the Sun and Moon (measuring the day, month and year), and were of importance to agricultural societies, in which the harvest depended on planting at the correct time of year. The most common modern calendar is based on the Roman calendar, which divided the year into twelve months of alternating thirty and thirty-one days apiece. In 46 BC Julius Caesar instigated calendar reform and adopted a calendar based upon the 3651⁄4 day year length originally proposed by 4th century BC Greek astronomer Callippus.
Lesson of the Day
What is naked eye astronomy?
Before there were telescopes early astronomers made some amazing observations by just observing the night sky. People looked at the stars for thousands of years without any optical aid. With a lot of perseverance they got some amazing results. They learned the apparent rotation of the stars, sun, moon and planets. It was counter intuitive to realize the Earth rotation so many early astronomers thought that our sky is revolving around us. Planets were special objects because they don't follow the same "sky paths" as normal stars. Without any optical aid, there are 5 visible planets. They look like bright stars.
What can we see with our naked eyes?
Are the stars colorful?
Yes, they are! The problem is that our eyes can't really figure out colors at low lights. With some experience, somebody can distinguish a red star (or planet) from a blue or white one. For example, Mars, Betelgeuse (in Orion), Alderbaran (in Taurus) are red objects.
Around 147 AD, Claudius Ptolemy (85 – 165AD), an Egyptian-born Greek with Roman citizenship, compiled a systematic summary of mathematical astronomy entitled Syntaxis Mathematica (Mathematical Collection).
The Earth, he argued, is a stationary sphere at the centre of a vastly larger celestial sphere that revolves at a perfectly uniform rate around the Earth, carrying with it the stars, planets, Sun, and Moon—thereby causing their daily risings and settings. Through the course of a year the Sun slowly traces out a great circle, known as the ecliptic, against the rotation of the celestial sphere. (The Moon and planets similarly travel backward—hence, the planets were also known as “wandering stars”—against the “fixed stars” found in the ecliptic.) The fundamental assumption of the Almagest is that the apparently irregular movements of the heavenly bodies are in reality combinations of regular, uniform, circular motions.
Ptolemy was preeminently responsible for the geocentric cosmology that prevailed in the Islamic world and in medieval Europe. He proposed what is now called the Ptolemaic system—a unified system in which each heavenly body is attached to its own sphere and the set of spheres nested so that it extends without gaps from the Earth to the celestial sphere. The numerical tables in the Almagest (which enabled planetary positions and other celestial phenomena to be calculated for arbitrary dates) had a profound influence on medieval astronomy. Ptolemy taught later astronomers how to use dated, quantitative observations to revise cosmological models.
Ptolemaic model was thoroughly accurate in predicting locations of planets and stars, and was almost unfalsifiable (and proved to only be falsifiable by more complexity of equipment -Galileo). The model wasn't challenged for 1300 years.
Video of the Day
Youth Ambassador Activity:
Introduce idea of overarching story line: travelling from the starting point of the run as the center of Earth’s observable universe to the ending point as the edge of the observable universe/big bang; see this picture for what I'm talking about: and imagine we're at the centre, running to the edge
See: Observable_universe_logarithmic_illustration.png [Wikimedia.org]
Star navigation activity with Sextant:
We need to learn how to use a sextant to navigate, then could use sextant to navigate to next night’s camp. Can double check accuracy with GPS?
We also found a video for how to make a sextant, which is kind of crafty but could be a school activity.