Скачать или смотреть Simple Armillary Sphere

Visualizing movements in the sky can be easily done with the help of this activity/model.

Gola Yantra (The armillary sphere) was in use in India since early times.

It finds its mention in the works of Aryabhata (476 CE).

Goladipika is a detailed treatise dealing with globes and armillary spheres.

It was mainly used as a teaching aid for students and not for any observational purpose.

We will use this simple setup to understand key concepts which were earlier explained with the help of Gola Yantra.

In the first part, we will focus on movement and position of the Sun.

In the second part, we will study the movement of the Moon, Nakshatra and other important constellations.

As usual let us start from the basics.


Position of the Sun
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This green ball will represent the celestial sphere.

This is the North celestial Pole and this is the South Celestial Pole.

Its apparent motion is from East to West.

When seen from the top it rotates in a clockwise direction.

This horizontal line represents the celestial equator.

This line represents the ecliptic, the path the sun takes on the celestial sphere throughout the year.


Let us mark points on the ecliptic at the interval of approximately 1 month.

Similarly also mark points on the equator at the distance of 1 hour or 15 degrees

One rotation of the celestial sphere marks approximately 24 hours or 1 day.

We will place the Sun at this point for now.

This point is known as the Vernal Equinox.

Point of intersection between Celestial equator and Ecliptic .

Each year this happens around the 21st of March.

One rotation is approximately 24 hours.

Every day the Sun travels around 1 degree on the ecliptic path.

It has moved here on 22nd March

Again one day is over.

It has moved 1 degree on the ecliptic.

And after 1 month, around 30 degrees on the ecliptic or here.

22nd April Sun will be here

22nd May Sun will be here

And the 21st June Sun will be here.

This is the Summer Solstice day. Longest day of the year.

From this day onwards , Sun begins its southern movement.

On 22nd July sun will be here

On 22nd Aug Sun will be here

Around 22nd Sep. Sun will be on the equator again. Autumn equinox. Day and nights are equal

Sun enters the Southern hemisphere en route to the Southernmost point.


22nd Oct

22nd Nov

22nd Dec.

Its southernmost point and Winter solstice. Shortest day in the Northern hemisphere on earth.

From this day, Sun starts its Northward travel also known as Uttarayan.

22nd Jan

22nd Feb

And 21st March . Vernal Equinox again.

This journey repeats forever all along.

Position of any celestial body can be addressed with the help of the equatorial coordinate system we explored earlier.

Starting from the vernal equinox point which is designated as 0h,

This point is 15 degrees or 1 hour away from the vernal equinox point along the equator.

Similarly markings represent 2h, 3h …. Till the 23rd hour to complete the circle again.

Declination is the distance from the equator. It's positive towards the North Pole while negative towards the south pole.

It is positive towards the North Celestial pole from 0 degrees at the equator to 90 degrees at the North Celestial Pole.

It is negative towards the South Pole from 0 degrees to minus ninety degrees towards the South Pole. We will not mark these on the green ball itself.

Note how the right ascension and declination values are changing for the Sun.

These points will be useful while positioning stars and planets on the celestial sphere.


Chapters:

00:00 Introduction
02:18 Right Ascension and Declination
03:17 Path of the Sun
05:43 Celestial Sphere and Location on Earth
08:39 Altitude of the Sun and Local Noon
10:11 Yearly position of the Rising Sun