Sun, Moon and Stars

Product Information

The most famous of these is Stonehenge in Wiltshire, Eng., where the original structure appears to have been built about 2000 bce and additions made at intervals several centuries later. It is composed of a series of holes, stones, and archways arranged mostly in circles, the outermost ring of holes having 56 marked positions, the inner ones 30 and 29, respectively. In addition, there is a large stone—the heel stone—set to the northeast, as well as some smaller stone markers. Observations were made by lining up holes or stones with the heel stone or one of the other markers and watching for the appearance of the Sun or Moon against that point on the horizon that lay in the same straight line. The extreme north and south positions on the horizon of the Sun—the summer and winter solstices—were particularly noted, while the inner circles, with their 29 and 30 marked positions, allowed “hollow” and “full” (29- or 30-day) lunar months to be counted off. More than 600 contemporaneous structures of an analogous but simpler kind have been discovered in Britain, in Brittany, and elsewhere in Europe and the Americas. It appears, then, that astronomical observation for calendrical purposes was a widespread practice in some temperate countries three to four millennia ago. Hipparchus, who flourished in Rhodes about 150 bce and was probably the greatest observational astronomer of antiquity, discovered from his own observations and those of others made over the previous 150 years that the equinoxes, where the ecliptic (the Sun’s apparent path) crosses the celestial equator (the celestial equivalent of the terrestrial Equator), were not fixed in space but moved slowly in a westerly direction. The movement is small, amounting to no more than 2° in 150 years, and it is known now as the precession of the equinoxes. Calendrically, it was an important discovery because the tropical year is measured with reference to the equinoxes, and precession reduced the value accepted by Callippus. Hipparchus calculated the tropical year to have a length of 365.242 days, which was very close to the present calculation of 365.242199 days; he also computed the precise length of a lunation, using a “great year” of four Callippic cycles. He arrived at the value of 29.53058 days for a lunation, which, again, is comparable with the present-day figure, 29.53059 days. At this point in the orbit, the Earth’s tilt means that the southern hemisphere is facing more towards the Sun. This means that the light and heat from the Sun is more direct and stronger. The days are the longest in the year and the nights, the shortest. This is summer in the southern hemisphere. In Scotland we experience winter at the beginning of the year. Six months later the Earth hastravelled halfway around its orbit. The southern hemisphere is now tilted away from the Sun so it is winter.At the same time it is summer in the northern hemisphere because it is now tilted more towards the Sun. Observation of the Sun is done at sunrise and sunset. When the Sun is low on the horizon, its path is narrow and obvious, but as it rises, it gets wider and wider. When it’s too high, you can’t tell where it has risen from and have to use other clues for navigation, such as the shape and direction of the waves. Phases of the Moon

The Metonic cycle was improved by both Callippus and Hipparchus. Callippus of Cyzicus ( c. 370–300 bce) was perhaps the foremost astronomer of his day. He formed what has been called the Callippic period, essentially a cycle of four Metonic periods. It was more accurate than the original Metonic cycle and made use of the fact that 365.25 days is a more precise value for the tropical year than 365 days. The Callippic period consisted of 4 × 235, or 940 lunar months, but its distribution of hollow and full months was different from Meton’s. Instead of having totals of 440 hollow and 500 full months, Callippus adopted 441 hollow and 499 full, thus reducing the length of four Metonic cycles by one day. The total days involved therefore became (441 × 29) + (499 × 30), or 27,759, and 27,759 ÷ (19 × 4) gives 365.25 days exactly. Thus the Callippic cycle fitted 940 lunar months precisely to 76 tropical years of 365.25 days.The month is determined by the Moon’s passage around the Earth, and, as in the case of the day, there are several ways in which it can be defined. In essence, these are of two kinds: first, the period taken by the Moon to complete an orbit of the Earth and, second, the time taken by the Moon to complete a cycle of phases. Among primitive societies, the month was determined from the phases; this interval, the synodic month, is now known to be 29.53059 days. The synodic month grew to be the basis of the calendar month. After summer it starts tilting away from the Sun again. The days get shorter and colder as we move into Autumn. Meanwhile, the northern hemisphere is tilted away from the Sun. The light and heat from the Sun is less direct, and it is spread over a wider area so it brings less warmth. The tilt means that nights are longer, days are shorter. This is winter in the northern hemisphere. Determining the Moon’s rising and setting points along with the rising and setting points of the fixed stars allows the Moon to be used to give direction during the night. The line separating light and dark in the Moon points approximately north and south since the Moon is positioned east or west of the Sun as it arcs through the night sky. The planets Let’s put a marker on Scotland. When this part of the Earth is facing the Sun it’s day time, when it’s facing away from the Sun that's night time.

The fact that neither months nor years occupied a whole number of days was recognized quite early in all the great civilizations. Some observers also realized that the difference between calendar dates and the celestial phenomena due to occur on them would first increase and then diminish until the two were once more in coincidence. The succession of differences and coincidences would be cyclic, recurring time and again as the years passed. An early recognition of this phenomenon was the Egyptian Sothic cycle, based on the star Sirius (called Sothis by the ancient Egyptians). The error with respect to the 365-day year and the heliacal risings of Sirius amounted to one day every four tropical years, or one whole Egyptian calendar year every 1,460 tropical years (4 × 365), which was equivalent to 1,461 Egyptian calendar years. After this period the heliacal rising and setting of Sothis would again coincide with the calendar dates ( see below The Egyptian calendar). The main use of cycles was to try to find some commensurable basis for lunar and solar calendars, and the best known of all the early attempts was the octaëteris, usually attributed to Cleostratus of Tenedos ( c. 500 bce) and Eudoxus of Cnidus (390– c. 340 bce). The cycle covered eight years, as its name implies, and so the octaëteris amounted to 8 × 365, or 2,920 days. This was very close to the total of 99 lunations (99 × 29.5 = 2,920.5 days), so this cycle gave a worthwhile link between lunar and solar calendars. When in the 4th century bce the accepted length of the year became 365.25 days, the total number of solar calendar days involved became 2,922, and it was then realized that the octaëteris was not as satisfactory a cycle as supposed.Another early and important cycle was the saros, essentially an eclipse cycle. There has been some confusion over its precise nature because the name is derived from the Babylonian word shār or shāru, which could mean either “universe” or the number 3,600 (i.e., 60 × 60). In the latter sense it was used by Berosus ( c. 290 bce) and a few later authors to refer to a period of 3,600 years. What is now known as the saros and appears as such in astronomical textbooks (still usually credited to the Babylonians) is a period of 18 years 11 1/ 3 days (or with one day more or less, depending on how many leap years are involved), after which a series of eclipses is repeated.

Today a solar calendar is kept in step with the seasons by a fixed rule of intercalation. But although the Egyptians, who used the heliacal rising of Sirius to determine the annual inundation of the Nile, knew that the tropical year was about 365.25 days in length, they still used a 365-day year without intercalation. This meant that the calendar date of Sirius’ rising became increasingly out of step with the original dates as the years progressed. In consequence, while the agricultural seasons were regulated by the heliacal rising of Sirius, the civil calendar ran its own separate course. It was not until well into Roman times that an intercalary day once every four years was instituted to retain coincidence. Complex cycles Venus – Kōpū – also known as Meremere-tū-ahiahi (evening star) and Tawera-i-te-atatū (morning star)

What Is the Average Temperature of Jupiter?

Summer is when the northern hemisphere is tilted towards the Sun - this gives us longer days and means the Sun's rays are more direct, stronger and warmer. The Earth spins three hundred and sixty five times in one year. That’s why we have three hundred and sixty five days in a year. While the Earth is spinning to give us day and night, it is also moving around the Sun. This movement is called an orbit. The line around which something spins is called an axis. The Earth's axis is tilted at an angle. The Earth’s tilt is the reason for the changing seasons. The Sun is a star, a giant ball of burning gas. The heat and light that it gives off helps to keep everything on our planet alive. When we see the Sun moving across the sky during the day it’s because the Earth is spinning, not the Sun.

Up here on the International Space Station I don’t get affected by the seasons but on Earth the seasons are always changing: Spring, Summer, Autumn and Winter.The northern hemisphere continues to tilt more and more towards the Sun, until the longest summer days in June.