The online celestial sphere simulations on this page help us to better understand what this representation of the sky consists of and what are some of the coordinate systems used to position celestial objects.

The celestial sphere is an imaginary representation of the sky used to study and understand astronomy. In this model, the Earth is considered to be at the center of a concentric sphere, and all celestial objects lie on its surface.

The celestial sphere is a useful tool for projecting and visualizing the position and motion of celestial bodies from the perspective of an observer on Earth. It is a convenient way to represent the appearance of the sky, although in reality we know that celestial objects are not physically located on a sphere.

This imaginary sphere is divided into various regions and coordinate systems to facilitate locating and tracking celestial objects. For example, the celestial equator is the imaginary circle that divides the sphere into two hemispheres: north and south. The celestial poles are the points where the Earth’s axis of rotation extends into the celestial sphere.

In addition, coordinates such as right ascension and declination are used to locate specific celestial objects on the celestial sphere. Right ascension is measured along the celestial equator and is expressed in hours, minutes and seconds, similar to the measurement of time. Declination is similar to terrestrial latitude and is measured in degrees.

The celestial sphere is a fundamental tool for astronomers, as it allows them to describe and predict the position of celestial objects, study their apparent motions and perform calculations on astronomical phenomena. It is also useful for navigation and orientation, as it provides stable reference points in relation to celestial objects.

In short, these online celestial sphere simulations are an excellent way to learn interactively what this representation of the sky and its coordinate systems are all about. Don’t miss them!

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- Equatorial
- Horizontal
- Constellations
- Ecliptic
- Pole

## Equatorial coordinate system

In the first of our online celestial sphere simulations, we study the equatorial coordinate system, which is the most basic coordinate system around the Earth. If you draw a large imaginary circle extending the Earth’s equator on the celestial sphere, it becomes the celestial equator. And if the north pole of the Earth is extended and marked on the celestial sphere, this point becomes the celestial north pole. Similarly, the point marked on the celestial sphere by extending the South Pole of the Earth is called the “South celestial pole”. The position of celestial bodies in the equatorial coordinate system is expressed in terms of right ascension and declination.

## Horizontal coordinate system

The horizontal coordinate system is a celestial coordinate system that uses the local horizon of the observer as the fundamental plane. The coordinates of an object in the sky are expressed in terms of altitude (or elevation) angle and azimuth.

## Constellations

If you look up at the sky where there is no light on a clear night, there are so many stars that you can’t count them. Thousands of years ago, the ancients linked the stars to create constellations with names of animals, objects and mythical figures. Each star in the constellation is only in a similar direction. Distances to the stars vary. There is no real connection between the stars in the constellation.

## The celestial equator and the ecliptic

The celestial equator is the extension of the Earth’s equator to the celestial sphere. Therefore, the celestial equator can be represented by a line fixed on the celestial sphere. The ecliptic is a line joining the place where the sun is located on the celestial globe during a year. The ecliptic can be represented by a line fixed on the celestial sphere. The Earth’s axis of rotation is tilted 23.5° with respect to the axis of revolution. Therefore, the celestial equator and the ecliptic are inclined 23.5° to each other.

## Pole Star

The Pole Star is located on an extension of the Earth’s axis of rotation and therefore helps us to know where north is. In this last of our online celestial sphere simulations, you can see how the position of the pole star in the sky changes as the observer’s latitude varies.