NASA’s Parker Solar Probe

In the 20th and 21st centuries, scientists have sent spacecraft to study the Sun close-up. In 1990, the Ulysses probe orbited the Sun three times. It helped determine that the Sun’s magnetic field reverses every 11 years.

On May 31, 2017, NASA has renamed the Solar Probe Plus spacecraft humanity's first mission to a star as the “Parker Solar Probe” in honor of American astrophysicist Eugene Parker.

Eugene Newman Parker developed the theory of the supersonic solar wind and predicted the Parker spiral shape of the solar magnetic field in the outer Solar System.

In 2018, NASA launched the Parker Solar Probe, which will travel far closer to the Sun than any other spacecraft.

NASA’s Parker Solar Probe mission will revolutionize human understanding of the Sun. The mission will “touch the Sun,” flying directly through the solar corona, facing brutal heat and radiation conditions and providing unprecedented, close-up observations of the star human live with.

With the cost of project US$1.5 billion, Parker Solar Probe was launched on 12 August 2018.
NASA’s Parker Solar Probe

Around 3500 BC: ancient Egyptian develop timekeeping device

Understand the time of day and the seasons was crucial for prehistoric man’s ability to comprehend on for survivals. Once agriculture was invented, the time to plant and harvest could only be predicted by following the changing rhythms of the universe from season to season.

The ancient Egyptians recorded their dates according to the regnal year of the reigning king. So when a new king entered the throne, they started counting ten years again from one.

The ancient Egyptians were the first to introduce the concept of twenty-four hours in a day. Night and day were both divided into twelve hours. Prior to 127 BC, the length of the hours varied depending on the season. Early time keeping devices and calendars depended on the movement of the Sun and Moon.

Around 3500 BC, one of the first timekeeping devices, the gnomon is developed in ancient Egypt.
A gnomon is composed of a vertical stick that casts a shadow on the ground or a stone base when left in the sunlight. Scholars estimate the time by looking at the position of the shadow.

The gnomon is a precursor to the sundial. A sundial is a device for measuring the hour of a day. In general, a sundial consists of the gnomon that is also called the style and the surface engraved with the timescale for indicating the time of a day.

The shadow of the gnomon is projected on the surface. When the sun moves in the sky, the corresponding gnomon’s shadow moves in the surface. According to the position of the gnomon’s shadow, the hour of a day is identified.

And by 1500 BC, in Egypt, the sticks were replaced with monumental decorated spires called obelisks, which were built in city centers.
Around 3500 BC: ancient Egyptian develop timekeeping device

Primitive Astronomical Notions

Primitive Astronomical Notions
On the astronomical side the most obvious fact is the division of time into periods of light and darkness by the apparent motion of the sun about the earth.

With closer attention it must soon have been observed that the relative length of day and night gradually changes, and that this change is attended by a wide range of remarkable phenomena.

At the time of shortest days, vegetable and animal life (in the north temperate zone) is checked by severe cold.

With gradually lengthening days, however, snow and ice sooner or latter disappear, vegetable is revived birds return from the warmer south, all nature is revived, birds return from the warmer south, all nature is quickened.

The longest days and those which succeed them are a period of excessive heat and of luxuriant vegetation, followed by harvest as the days shorten, towards the completion of the great annual cycle.

In time, closer observers, noting the stars, discovered hat corresponding with this great periodic change are gradual variations in the starry hemisphere visible at night, that in other words the sun’s place among the stars is progressively changing, that it is in fact describing a path completed in a large number of days, which after many years of counting is found to be 365.

It is also found that the midday height of the sun above the southern horizon shares in the annual cycle.

The determination of the number of days on the year is a matter of very gradual approximation, possible only to men who have already attained some command of numbers and the habit of preserving records extending over a long series of years.

For there is now well marked beginning of the year as of the day.

An erroneous determination of the number of days becomes apparent only after a number of years increasing with accuracy of the original approximation.

Still another natural period is introduced by the motion of the moon, which seems like the sin to have a daily motion about the earth, and also to describe a closed path among the stars in a period of about 29 days.

Unlike the sun, however, the moon has during this period a remarkable change of apparent shape and luminosity from “new” to “full” and back again.

The difficulty of expressing the precise length of the month and the year in days, causing the imperfection of of early calendars, has on the other hand reacted to the advantage of mathematical astronomy by demanding more and and more precise both in observation and in the computation based on it.
Primitive Astronomical Notions