Editing: Celsius (temperature)

# Celsius (Temperature Scale)

**Celsius** is a temperature scale where water freezes at 0 degrees and boils at 100 degrees under standard atmospheric pressure. Named after Swedish astronomer Anders Celsius, it is the primary temperature measurement system used in most countries worldwide and one of two temperature scales in the International System of Units (SI), alongside the Kelvin scale [1][3].

The Celsius scale, denoted by the symbol °C, provides an intuitive reference system based on the phase transitions of water—the most familiar substance in everyday life. This makes it particularly practical for weather reporting, cooking, medical applications, and general scientific use outside of specialized physics research.

## History and Development

Anders Celsius invented the temperature scale in 1742 while working as an astronomer at Uppsala University in Sweden [3][7]. Interestingly, Celsius originally defined his scale in reverse: 100 degrees for the freezing point of water and 0 degrees for the boiling point. This counterintuitive arrangement was later reversed by other scientists, including Carl Linnaeus, to create the modern Celsius scale we use today.

The scale was historically known as the **centigrade scale** in English-speaking countries, derived from the Latin words "centum" (hundred) and "gradus" (steps), referring to the 100-degree interval between the freezing and boiling points of water [1][3]. The name was officially changed to Celsius in 1948 by the General Conference on Weights and Measures to honor its inventor and avoid confusion with other centigrade scales.

## Scientific Foundation

The Celsius scale is defined by two fixed reference points under standard atmospheric pressure (1 atmosphere or 101.325 kPa):
- **0°C**: The freezing point of pure water
- **100°C**: The boiling point of pure water

This creates exactly 100 equal divisions between these two fundamental phase transitions, making calculations and conversions relatively straightforward [5]. The scale is considered an **empirical scale** because it developed historically based on observable physical phenomena rather than theoretical principles.

In modern scientific practice, the Celsius scale is formally defined in relation to the Kelvin scale, which is based on absolute zero (-273.15°C). One degree Celsius is exactly equal to one Kelvin in terms of temperature difference, but the scales have different zero points.

## Conversion Formulas

Converting between Celsius and other temperature scales requires specific mathematical relationships:

**Celsius to Fahrenheit**: °F = (°C × 9/5) + 32
**Fahrenheit to Celsius**: °C = (°F - 32) × 5/9
**Celsius to Kelvin**: K = °C + 273.15
**Kelvin to Celsius**: °C = K - 273.15

These conversions are essential in international science, engineering, and commerce, where different regions may use different temperature scales [8].

## Global Usage and Applications

Celsius is the standard temperature scale in most countries worldwide, with the notable exceptions of the United States, Liberia, and Myanmar, which primarily use Fahrenheit for everyday measurements. The scale dominates in:

- **Weather reporting**: Most global meteorological services report temperatures in Celsius
- **Medical applications**: Body temperature, vaccine storage, and medical equipment calibration
- **Cooking and food safety**: Oven temperatures, food storage, and pasteurization standards
- **Scientific research**: Laboratory work, chemical processes, and environmental monitoring
- **Industrial processes**: Manufacturing quality control and equipment specifications

The widespread adoption of Celsius reflects its practical advantages: the 0-100 range covers most temperatures encountered in daily life, and the water-based reference points are universally meaningful.

## Relationship to Other Temperature Scales

While Celsius serves everyday needs effectively, scientific applications often require other scales. The **Kelvin scale** uses the same degree increment as Celsius but starts at absolute zero, making it essential for thermodynamics and physics calculations. **Fahrenheit** provides finer gradation for human comfort ranges—the difference between 70°F and 71°F (about 0.6°C) is more perceptible than a full degree Celsius change.

The choice of temperature scale often reflects cultural, historical, and practical considerations rather than purely scientific ones. However, Celsius strikes an optimal balance between scientific utility and everyday practicality, explaining its global dominance.

## Related Topics

- Fahrenheit temperature scale
- Kelvin temperature scale
- Anders Celsius
- Thermodynamics
- International System of Units (SI)
- Temperature measurement
- Weather forecasting
- Absolute zero

## Summary

Celsius is a temperature scale based on water's freezing point (0°C) and boiling point (100°C), invented by Anders Celsius in 1742 and now used as the primary temperature measurement system in most countries worldwide.

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