Package 'astronomR'

Retrieve the Value of a Physical Constant

Description

Retrieves the value and unit of a specified physical constant from the constants_df dataset. You can search by the constant's name and choose whether to retrieve the value in SI units or natural units.

Usage

constant_value(constant_name, unit = "SI")

Arguments

constant_name	Character. The name (or part of the name) of the constant to search for. Case-insensitive and partial matches are allowed.
unit	Character. The unit system to retrieve the constant in. Options are: "SI": Retrieves the value in SI units (default). "Natural": Retrieves the value in natural units.

Value

A list containing:

• name: The full name of the constant.

• value: The numeric value of the constant.

• unit: The unit string for the selected unit system.

Examples

constant_value("speed of light", unit = "SI")
constant_value("planck", unit = "SI")
constant_value("electron mass", unit = "Natural")

---

Fundamental Physical Constants in SI and Natural Units

Description

A dataset containing commonly used physical constants in both SI units and natural units. The dataset includes the constant's name, symbol, value in SI units, SI unit, value in natural units, and natural unit representation.

Usage

constants_df

Format

A tibble with 19 rows and 6 columns:

name

Character. Name of the physical constant.

symbol

Character. Symbol representing the constant.

value_SI

Numeric. The value of the constant in SI units.

unit_SI

Character. The SI unit for the constant.

value_Natural

Numeric. The value of the constant in natural units.

unit_Natural

Character. The unit of the constant in natural units.

Examples

constants_df

---

Convert Decimal Degrees to Degrees, Minutes, and Seconds (DMS) Format

Description

Converts a decimal degree angle to the Degrees-Minutes-Seconds (DMS) format commonly used in astronomy for expressing declination and other angles.

Usage

deg_to_dms(deg, type = "cat", digit = 5)

Arguments

deg	Numeric vector of angles in decimal degrees. All values must be between -90 and 90.
type	Character string specifying the output format. Options are: "cat" (default): Prints the angle as a formatted string in DMS notation. "mat": Returns a matrix with columns for sign, degrees, minutes, and seconds.
digit	Integer specifying the number of digits to round the seconds to. Default is 5.

Value

When type = "cat", prints the DMS string and returns NULL invisibly. When type = "mat", returns a character matrix with columns SIGN, DEG, MIN, and SEC.

Examples

deg_to_dms(45.5042)
deg_to_dms(-12.5, type = "mat")
deg_to_dms(c(10.25, 45.5), type = "mat")

---

Convert Decimal Degrees to Hours, Minutes, and Seconds (HMS) Format

Description

Converts a decimal degree angle to Hours-Minutes-Seconds (HMS) format, which is used in astronomy to express Right Ascension (RA).

Usage

deg_to_hms(deg, type = "cat", digit = 5)

Arguments

deg	Numeric vector of angles in decimal degrees. Values can range from 0 to 360.
type	Character string specifying the output format. Options are: "cat" (default): Prints a formatted string (e.g., 3H0M0S). "mat": Returns a matrix with columns for hours, minutes, and seconds.
digit	Integer specifying the number of decimal places to round seconds to. Default is 5.

Value

When type = "cat", prints the HMS string and returns NULL invisibly. When type = "mat", returns a numeric matrix with columns HRS, MIN, and SEC.

Examples

deg_to_hms(deg = 45)
deg_to_hms(deg = 45, type = "mat")
deg_to_hms(deg = 177.74208, digit = 3)

---

Convert Degrees to Radians

Description

Converts angles from degrees to radians. Supports vectorized input.

Usage

deg2rad(deg)

Arguments

deg	Numeric. The angle(s) in degrees to convert to radians.

Value

Numeric. The corresponding angle(s) in radians.

Examples

deg2rad(180)
deg2rad(c(0, 90, 180))

---

Convert Degrees, Minutes, and Seconds (DMS) to Decimal Degrees

Description

Converts an angle expressed in Degrees-Minutes-Seconds (DMS) format to decimal degrees. Accepts either separate numeric arguments or a single formatted string.

Usage

dms_to_deg(d, m, s, digit = 5)

Arguments

d	Numeric or character. The degrees component. If a single character string is provided (e.g., "12\u00B034'56\""), the degrees, minutes, and seconds are parsed automatically, and m and s should be omitted.
m	Numeric. The minutes component. Must be less than 60. Optional when d is a string.
s	Numeric. The seconds component. Must be less than 60. Optional when d is a string.
digit	Integer. Number of decimal places to round the result to. Default is 5.

Value

Numeric. The angle in decimal degrees.

Examples

dms_to_deg(d = 12, m = 34, s = 56)
dms_to_deg(d = "12\u00B034'56\"", digit = 3)

---

Estimate the Number of Communicating Civilizations via the Drake Equation

Description

Computes **N**, the estimated number of active, technologically advanced civilizations capable of interstellar communication in the Milky Way, using the Drake equation:

Usage

drake_equation(
  R_star = 1.5,
  fp = 1,
  ne = 0.4,
  fl = 1,
  fi = 1,
  fc = 0.1,
  L = 1000
)

Arguments

R_star	Numeric. Average rate of star formation per year in the Milky Way (stars yr$^{-1}$). Default: 1.5.
fp	Numeric. Fraction of stars that have planetary systems. Must be in $[0, 1]$. Default: 1.0 (current exoplanet surveys suggest nearly all Sun-like stars host planets).
ne	Numeric. Mean number of planets per planetary system that could potentially support life (Earth-like / habitable-zone planets). Default: 0.4.
fl	Numeric. Fraction of suitable planets on which life actually appears. Must be in $[0, 1]$. Default: 1.0.
fi	Numeric. Fraction of life-bearing planets on which intelligent life evolves. Must be in $[0, 1]$. Default: 1.0.
fc	Numeric. Fraction of intelligent civilizations that develop detectable communication technology. Must be in $[0, 1]$. Default: 0.1.
L	Numeric. Mean longevity (years) of a communicating civilization. Default: 1000.

Details

$N = R_* \times f_p \times n_e \times f_l \times f_i \times f_c \times L$

Default values reflect widely cited contemporary estimates (see References). All fraction parameters must lie in $[0, 1]$.

Value

A named list with the following elements:

N

Numeric. Estimated number of communicating civilizations.

inputs

Named numeric vector of all seven input parameters.

equation

Character. Human-readable form of the equation with values substituted.

interpretation

Character. A qualitative interpretation of N spanning six tiers from effectively zero ($N < 0.001$) to galaxy teeming with life ($N \geq 10{,}000$).

References

Drake, F. D. (1961). Discussion at the first SETI conference, Green Bank, West Virginia. NRAO.

Vakoch, D. A., & Dowd, M. F. (Eds.) (2015). The Drake Equation: Estimating the Prevalence of Extraterrestrial Life through the Ages. Cambridge University Press.

Examples

# Using all defaults (optimistic estimate)
drake_equation()

# Pessimistic "Rare Earth" scenario
drake_equation(R_star = 1.5, fp = 1.0, ne = 0.4,
               fl = 0.01, fi = 0.01, fc = 0.01, L = 304)

# Custom values
result <- drake_equation(R_star = 3, fp = 0.9, ne = 0.5,
                         fl = 0.5, fi = 0.1, fc = 0.1, L = 10000)
result$N

---

Query Gaia Archive Data

Description

Queries the Gaia Archive TAP service to retrieve stellar data based on specified variables and filter conditions. Uses the Gaia Early Data Release 3 (EDR3) catalog.

Usage

get_gaia_data(vars, condition)

Arguments

vars	A character string specifying the variables (columns) to retrieve, separated by commas (e.g., "source_id, ra, dec").
condition	A character string specifying the SQL WHERE clause used to filter rows (e.g., "parallax > 10").

Details

This function sends a synchronous ADQL query to the Gaia Archive TAP service at https://gea.esac.esa.int/tap-server/tap/sync. An internet connection is required.

Value

A data frame containing the requested columns for all rows matching condition.

Examples

vars <- "source_id, ra, dec, phot_bp_mean_mag, phot_rp_mean_mag, parallax"
condition <- "parallax > 40"
result <- get_gaia_data(vars, condition)
head(result)

---

Convert Hours, Minutes, and Seconds (HMS) to Decimal Degrees

Description

Converts an angle expressed in Hours-Minutes-Seconds (HMS) format to decimal degrees. Accepts either separate numeric arguments or a single formatted string.

Usage

hms_to_deg(h, m, s, digit = 5)

Arguments

h	Numeric or character. The hours component. If a single character string is provided (e.g., "03h15m30s"), the hours, minutes, and seconds are parsed automatically, and m and s should be omitted.
m	Numeric. The minutes component. Optional when h is a string.
s	Numeric. The seconds component. Optional when h is a string.
digit	Integer. Number of decimal places to round the result to. Default is 5.

Value

Numeric. The angle in decimal degrees.

Examples

hms_to_deg(h = 3, m = 15, s = 30)
hms_to_deg(h = 3, m = 15, s = 30.123)
hms_to_deg(h = "03h15m30s")

---

Convert Kilometers to Megaparsecs

Description

This function converts a distance value from kilometers (km) to megaparsecs (Mpc). The conversion factor is based on 1 parsec being equivalent to 3.262 light-years, and 1 light-year being approximately $9.461 \times 10^{12}$ kilometers.

Usage

km_to_Mpc(km)

Arguments

km	A numeric value representing the distance in kilometers.

Value

A numeric value representing the equivalent distance in megaparsecs (Mpc).

Examples

km_to_Mpc(3.086e19) # Converts 3.086e19 km (approx. 1 Mpc) to megaparsecs

---

Convert Megaparsecs to Kilometers

Description

This function converts a distance value from megaparsecs (Mpc) to kilometers (km). The conversion factor is based on 1 parsec being equivalent to 3.262 light-years, and 1 light-year being approximately $9.461 \times 10^{12}$ kilometers.

Usage

Mpc_to_km(mpc)

Arguments

mpc	A numeric value representing the distance in megaparsecs.

Value

A numeric value representing the equivalent distance in kilometers (km).

Examples

Mpc_to_km(1) # Converts 1 Mpc to kilometers

---

Photon Energy Density as a Function of Temperature

Description

Calculates the photon energy density for a given temperature $T$, using $\rho_\gamma = \frac{\pi^2}{15} T^4$.

Usage

photon_energy_density_fn_T(temp, unit = "eV")

Arguments

temp	Numeric. Temperature in either eV or Kelvin.
unit	Character. The unit of the temperature input. Either "eV" (default) or "K".

Value

Numeric. The photon energy density in natural units.

Examples

photon_energy_density_fn_T(1, "eV")
photon_energy_density_fn_T(300, "K")

---

Photon Energy Density as a Function of Redshift

Description

Calculates the photon energy density at a given cosmological redshift $z$ by first converting to temperature in eV.

Usage

photon_energy_density_fn_z(z)

Arguments

z	Numeric. The redshift value.

Value

Numeric. The photon energy density in natural units.

Examples

photon_energy_density_fn_z(1300)

---

Photon Number Density as a Function of Temperature

Description

Calculates the photon number density for a given temperature $T$, using $n_\gamma = \frac{2\zeta(3)}{\pi^2} T^3$.

Usage

photon_number_density_fn_T(temp, unit = "eV")

Arguments

temp	Numeric. Temperature in either eV or Kelvin.
unit	Character. The unit of the temperature input. Either "eV" (default) or "K".

Value

Numeric. The photon number density in natural units.

Examples

photon_number_density_fn_T(1, "eV")
photon_number_density_fn_T(300, "K")

---

Photon Number Density as a Function of Redshift

Description

Calculates the photon number density at a given cosmological redshift $z$ by first converting to temperature in eV.

Usage

photon_number_density_fn_z(z)

Arguments

z	Numeric. The redshift value.

Value

Numeric. The photon number density in natural units.

Examples

photon_number_density_fn_z(1300)

---

Convert Radians to Degrees

Description

Converts angles from radians to degrees. Supports vectorized input.

Usage

rad2deg(rad)

Arguments

rad	Numeric. The angle(s) in radians to convert to degrees.

Value

Numeric. The corresponding angle(s) in degrees.

Examples

rad2deg(pi)
rad2deg(c(0, pi / 2, pi))

---

Ionization Fraction Using the Saha Equation

Description

Calculates the ionization fraction $X_e$ as a function of redshift $z$ using the Saha equation for hydrogen recombination.

Usage

Saha_Xe(z)

Arguments

z	Numeric. The redshift value.

Value

Numeric. The ionization fraction $X_e$ (between 0 and 1).

Examples

Saha_Xe(1300)
Saha_Xe(1100)

---

Deviation of Ionization Fraction from 0.5

Description

Returns $X_e(z) - 0.5$, useful for finding the redshift at which the ionization fraction equals 0.5 (e.g., via root-finding).

Usage

soln_saha(z)

Arguments

z	Numeric. The redshift value.

Value

Numeric. $X_e - 0.5$.

Examples

soln_saha(1350)

---