SciPy - Astronomical Constants

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What are Astronomical Constants?

Astronomical constants are fundamental and fixed values that represent key physical quantities essential for understanding and describing celestial phenomena in fields such as astrophysics, astronomy and cosmology.

These constants provide standardized measures for various properties of celestial objects and events by facilitating precise and consistent scientific calculations.

Following are the purpose and importance of Astronomical Constants −

• Uniformity: Astronomical constants offer a uniform basis for comparing different measurements and phenomena across the universe. This standardization is crucial for ensuring consistency in scientific research and communication.
• Precision: By using well-defined constants the scientists can perform calculations with high precision. This is particularly important when dealing with vast distances, massive objects and intricate interactions in space.
• Benchmarking: Constants such as the astronomical unit (AU) and light year serve as benchmarks for measuring and comparing the sizes, distances and scales of celestial objects and events.

Types of Astronomical Constants in SciPy

The scipy.constants module provides several key types that are critical for various astronomical calculations. Let's see them in detail with examples −

Astronomical Unit (AU)

The Astronomical Unit (AU) is a fundamental unit of distance used in astronomy to describe the average distance between the Earth and the Sun. It provides a convenient way to express and compare distances within our solar system and beyond.

In SciPy the Astronomical Unit is represented by the constant scipy.constants.astronomical_unit and has a value of approximately 1.495978707 10 meters.

Example

Following is the example which print the value of one Astronomical Unit in meters by providing a clear reference for scientific calculations involving solar system distances −

from scipy.constants import astronomical_unit

# Example usage
print(f"1 Astronomical Unit (AU) = {astronomical_unit} meters")

Following is the output of printing the Astronomical Unit −

1 Astronomical Unit (AU) = 149597870700.0 meters

Light Year

The Light Year is a unit of distance used in astronomy to measure the vast spaces between celestial objects. It represents the distance that light travels in one Julian year in a vacuum by making it an ideal unit for expressing astronomical distances due to the immense scales involved.

In SciPy the Light Year is represented by the constant scipy.constants.light_year and has a value of approximately 9.460730472 10 meters.

Example

Below is the example which provides the output value of one Light Year in meters which helps to contextualize distances in a standard unit of measurement −

from scipy.constants import light_year

# Example usage
print(f"1 Light Year = {light_year} meters")

Below is the output of calculating the light_year −

1 Light Year = 9460730472580800.0 meters

Parsec

The Parsec is a unit of length used in astronomy to measure large distances to astronomical objects outside the Solar System. It is defined based on the method of parallax which involves the apparent shift in position of a nearby star against the background of more distant stars as observed from Earth.

In SciPy the parsec is represented by the constant scipy.constants.parsec and has a value of approximately 3.085677581 10 meters.

Example

Here in this example we are calculating the distance to a star that is 4 parsecs away in light-years −

from scipy.constants import parsec, light_year

# Distance in parsecs
distance_pc = 4

# Convert to light-years
distance_ly = distance_pc * (parsec / light_year)
print(f"Distance to the star is {distance_ly:.2f} light-years")

The output of parsecs is given as follows −

Distance to the star is 13.05 light-years

Standard Gravity

In SciPy scipy.constants.g represents the standard acceleration due to gravity on Earth's surface. This is a commonly used constant in physics and engineering for calculations involving gravitational force, free-fall and related phenomena. Generally the value is given as 9.80665 m/s.

Example

Here in this example we show how to calculate the time it takes for an object to fall from a certain height under Earth's gravity −

from scipy.constants import g

# Given height (in meters)
height = 100  # e.g., 100 meters

# Time to fall (using the formula: t = sqrt(2 * height / g))
fall_time = (2 * height / g) ** 0.5

print(f"Time to fall from {height} meters: {fall_time:.2f} seconds")

The Standard Gravity output is given as follows −

Time to fall from 100 meters: 4.52 seconds

Julian Year

A Julian year is a unit of time used in astronomy and is defined to be exactly 365.25 days. This unit is used to simplify time-related calculations in celestial mechanics such as orbital periods where precise timekeeping is crucial.

In SciPy the Julian year is represented as a constant in the scipy.constants module and generally the value of 1 Julian year is given as 3.15576 10 seconds.

Example

Following is the example which is used to calculate the number of seconds in 10 Julian years with the help of scipy.constants.Julian_year −

from scipy.constants import Julian_year

# Calculate seconds in 10 Julian years
seconds_in_10_years = 10 * Julian_year

print(f"10 Julian Years = {seconds_in_10_years:.2e} seconds")

The output of the above program is as follows −

10 Julian Years = 3.16e+08 seconds

List of Astronomical Constants

Here in this tutorial we discussed about only few Astronomical constants which can be used with the help of SciPy library. There are many other such as Day, Mean Radius of Earth and so on.

We can get all the constants available in the scipy.constants module with the help of below code −

import scipy
from scipy import constants
print(dir(scipy.constants))

Following are the constants list −

['Avogadro', 'Boltzmann', 'Btu', 'Btu_IT', 'Btu_th', 'ConstantWarning', 'G', 'Julian_year', 'N_A', 'Planck', 'R', 'Rydberg', 'Stefan_Boltzmann', 'Wien', '__all__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__path__', '__spec__', '_codata', '_constants', '_obsolete_constants', 'acre', 'alpha', 'angstrom', 'arcmin', 'arcminute', 'arcsec', 'arcsecond', 'astronomical_unit',.....................................
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 'u', 'unit', 'value', 'week', 'yard', 'year', 'yobi', 'yocto', 'yotta', 'zebi', 'zepto', 'zero_Celsius', 'zetta']