Astronomical Distance Converter

An astronomical distance converter expresses the same physical length in another unit, such as kilometers, astronomical units, light-years, or parsecs. Enter a distance, select its current unit, and choose an output unit. A reliable conversion uses documented definitions, retains precision during calculation, and does not imply that a rounded or uncertain astronomical measurement has become more accurate.

Key Takeaways

• Use kilometers for local spaceflight scales, astronomical units for solar-system distances, and light-years or parsecs for interstellar distances.
• Unit conversion changes how a distance is written; it does not change the physical distance or improve its measurement accuracy.
• The astronomical unit has an exact value in meters, while the parsec has an exact mathematical relationship to the astronomical unit.
• Light-seconds, light-minutes, and light-years are units of distance, even though their names contain time units.
• Redshift and the current separation of moving planets cannot be determined through unit conversion alone.

This guide explains how the converter works, which units it supports, how to select a useful output unit, how to verify the arithmetic, and where ordinary unit conversion ends and specialized astronomical modeling begins.

Calculation standard: The converter first normalizes each input to meters and then converts that meter value into the selected output unit. Intermediate values are not rounded. Displayed results should be rounded according to the precision of the input and the purpose of the result.

How Do You Use the Astronomical Distance Converter?

Enter the numerical distance, select the source unit, and choose the target unit. Before accepting the result, confirm that the input unit and stated precision match the original source.

Step 1: Enter the Distance

Enter a finite, non-negative number.

Examples include:

• 384400 kilometers
• 1 astronomical unit
• 4.24 light-years
• 2.637 parsecs
• 8.2 kiloparsecs
• 100 megaparsecs

A value of zero converts to zero in every distance unit. A negative number does not represent an ordinary physical path length and should not be treated as a valid astronomical distance.

Scientific notation is useful for very large or very small values. For example:

[4.01135\times10^{13}\ \text{km}]

is a compact way to write approximately 40.1 trillion kilometers.

Step 2: Select the Source Unit

The source unit must match the entered value.

Entering 149597870.7 as kilometers represents exactly one astronomical unit. Entering the same number as miles represents a much greater distance.

A converter cannot determine the intended unit from the number alone.

Step 3: Select the Target Unit

Choose an output unit that suits the scale and intended audience.

Typical choices are:

• kilometers for spacecraft and nearby solar-system distances
• miles for readers who use U.S. customary units
• astronomical units for planetary orbits and solar-system comparisons
• light-seconds, light-minutes, or light-hours for signal-scale distances
• light-years for accessible descriptions of stellar distances
• parsecs for astrometry and professional astronomy
• kiloparsecs for galactic structure
• megaparsecs or gigaparsecs for extragalactic and cosmological scales

Step 4: Review the Significant Figures

A conversion can generate many decimal places, but those digits are not necessarily meaningful.

For example:

[4.2\ \text{ly}\approx1.287725854\ \text{pc}]

The arithmetic is valid, but the input contains only two significant figures. A defensible displayed result is therefore:

[4.2\ \text{ly}\approx1.3\ \text{pc}]

Step 5: Confirm That You Need Conversion Rather Than a New Distance

A converter answers:

How can this known distance be expressed in another unit?

It does not answer:

What is the current distance between two moving objects?

A current planet, moon, asteroid, or spacecraft distance must first be obtained from an ephemeris or orbital calculation.

How Does the Astronomical Distance Converter Work?

The converter uses meters as a common intermediate unit.

Let:

• (x_s) be the entered numerical value
• (F_s) be the number of meters in one source unit
• (F_t) be the number of meters in one target unit
• (x_t) be the converted numerical value

Then:

[x_tx_s\times\frac{F_s}{F_t}]

This common-base method is easier to audit than maintaining a separate formula for every possible pair of units.

Example: Converting 2 Astronomical Units to Kilometers

One astronomical unit is exactly:

[149{,}597{,}870{,}700\ \text{m}]

Therefore:

[2\ \text{au}\times\frac{149{,}597{,}870{,}700\ \text{m}}{1\ \text{au}}\times\frac{1\ \text{km}}{1{,}000\ \text{m}}]

[299{,}195{,}741.4\ \text{km}]

The physical distance has not changed. Only its numerical representation and unit have changed.

Which Units Does the Converter Support?

The converter described on this page supports the following distance units.

Scale group	Supported units
Terrestrial and spacecraft scale	meters, kilometers, international miles
Solar-system scale	astronomical units
Light-distance scale	light-seconds, light-minutes, light-hours, light-days, light-years
Stellar and galactic scale	parsecs, kiloparsecs, megaparsecs, gigaparsecs

All of these are units of length.

A light-minute, for example, is not a duration in this context. It is the distance that light travels through a vacuum during 60 seconds.

Unit Symbols and Capitalization

Unit	Recommended symbol
meter	m
kilometer	km
international mile	mi
astronomical unit	au
light-year	ly
parsec	pc
kiloparsec	kpc
megaparsec	Mpc
gigaparsec	Gpc

Capitalization matters for metric prefixes:

• k means kilo, or (10^3)
• M means mega, or (10^6)
• G means giga, or (10^9)

Therefore, Mpc means megaparsec. Writing mpc would indicate a different prefix and should not be treated as an equivalent symbol.

The International Astronomical Union recommends the lowercase symbol au, although uppercase AU remains common in general writing and search queries.

Which Unit Definitions Are Used?

The following standards provide the conversion basis used throughout this guide.

Unit	Value in meters	Treatment
meter	(1)	SI base unit
kilometer	(1{,}000)	Exact
international mile	(1{,}609.344)	Exact
astronomical unit	(149{,}597{,}870{,}700)	Exact
light-second	(299{,}792{,}458)	Exact
light-minute	(17{,}987{,}547{,}480)	Exact
light-hour	(1{,}079{,}252{,}848{,}800)	Exact
light-day	(25{,}902{,}068{,}371{,}200)	Exact
light-year	(9{,}460{,}730{,}472{,}580{,}800)	Exact under the stated Julian-year convention
parsec	(\frac{648{,}000}{\pi}\ \text{au})	Exact relation; decimal representation is approximate
kiloparsec	(1{,}000\ \text{pc})	Exact decimal multiple
megaparsec	(1{,}000{,}000\ \text{pc})	Exact decimal multiple
gigaparsec	(1{,}000{,}000{,}000\ \text{pc})	Exact decimal multiple

The international mile is exactly 1,609.344 meters under the modern international definition. The NIST Guide to the SI distinguishes it from the older U.S. survey mile used in some historical surveying records.

Why Is the Speed of Light Exact?

The Bureau International des Poids et Mesures definition of the metre fixes the speed of light in vacuum at exactly:

[c299{,}792{,}458\ \text{m/s}]

This gives exact light-distance relationships such as:

[1\ \text{light-second}299{,}792{,}458\ \text{m}]

and:

[1\ \text{light-minute}60\ \text{light-seconds}]

The exactness applies to the unit definition. It does not make a measured stellar or planetary distance exact.

How Is the Astronomical Unit Defined?

The astronomical unit is a fixed unit of length.

The International Astronomical Union’s 2012 Resolution B2 defines:

[1\ \text{au}149{,}597{,}870{,}700\ \text{m}]

Therefore:

[1\ \text{au}149{,}597{,}870.7\ \text{km}]

The astronomical unit is not defined as Earth’s current distance from the Sun. Earth moves along a noncircular orbit, so the instantaneous Sun–Earth distance changes while the unit remains fixed.

How Is a Light-Year Defined?

A light-year is the distance light travels through a vacuum in one Julian year.

This converter adopts:

[1\ \text{Julian year}365.25\ \text{days}]

and:

[1\ \text{day}86{,}400\ \text{s}]

Therefore:

[1\ \text{Julian year}31{,}557{,}600\ \text{s}]

Multiplying by the exact speed of light gives:

[1\ \text{ly}299{,}792{,}458\times31{,}557{,}600\ \text{m}][1\ \text{ly}

9{,}460{,}730{,}472{,}580{,}800\ \text{m}]

or:

[1\ \text{ly}9{,}460{,}730{,}472{,}580.8\ \text{km}]

A light-year is a distance. A statement such as “the star is four light-years away” does not mean that a spacecraft would reach it in four years.

How Is a Parsec Defined?

A parsec is an astronomical unit of length connected to a parallax angle of one arcsecond.

For unit conversion, the exact relationship adopted through IAU 2015 Resolution B2 is:

[1\ \text{pc}\frac{648{,}000}{\pi}\ \text{au}]

The resolution text and supporting explanation are reproduced in the accompanying paper, IAU 2015 Resolution B2 on bolometric magnitude scales.

Using the exact astronomical-unit value:

[1\ \text{pc}\approx206{,}264.806247096\ \text{au}]

[1\ \text{pc}\approx3.085677581491367\times10^{16}\ \text{m}]

and:

[1\ \text{pc}\approx3.261563777167\ \text{ly}]

The relationship involving (\pi) is exact. Its decimal representation continues indefinitely and must be rounded for display.

NASA’s Universe Glossary describes a parsec as the distance associated with a parallax of one arcsecond and gives the commonly rounded value of 3.262 light-years.

Which Astronomical Distance Unit Should You Choose?

Choose a unit that keeps the number readable, fits the scientific context, and does not imply more precision than the source supports.

The Scale–Purpose–Precision Framework

A practical unit choice can be made with three checks:

1. Scale: How large is the distance?
2. Purpose: Who will read or use the result?
3. Precision: How accurately is the source distance known?

Situation	Usually useful unit	Reason
Satellite altitude or nearby spacecraft range	km	Compact and familiar
General U.S. audience comparison	mi	Familiar customary unit
Planetary orbit or solar-system distance	au	Keeps values manageable
Signal-scale solar-system distance	light-seconds or light-minutes	Shows propagation scale
Nearby star for general readers	ly	Intuitive connection to light travel
Stellar catalog or parallax work	pc	Standard astrometric unit
Structure within a galaxy	kpc	Avoids large parsec values
Distance between galaxies	Mpc	Standard extragalactic scale
Largest modeled cosmic scales	Gpc	Keeps billion-parsec values readable

These are practical recommendations rather than mathematical restrictions. Any distance can be expressed in any compatible distance unit.

Which Is Better: Light-Years or Parsecs?

Neither unit is universally better.

Light-years	Parsecs
Familiar to general readers	Common in professional astronomy
Makes light-travel scale intuitive	Connected directly to parallax conventions
Common in educational writing	Used extensively in catalogs and research
Convenient for nearby stars	Extends naturally to kpc, Mpc, and Gpc

Use light-years when immediate interpretation matters most. Use parsecs when working with astrometry, scientific catalogs, galactic structure, or professional literature.

Astronomical Distance Conversion Reference Table

The following values are calculated from the definitions stated above.

Starting distance	Kilometers	Astronomical units	Light-years	Parsecs
1 au	149,597,870.7	1	0.00001581250741	0.000004848136811
1 ly	9,460,730,472,580.8	63,241.07708	1	0.3066013938
1 pc	30,856,775,814,913.67	206,264.8062	3.261563777	1
1 kpc	(3.085677581\times10^{16})	(2.062648062\times10^8)	3,261.563777	1,000
1 Mpc	(3.085677581\times10^{19})	(2.062648062\times10^{11})	3,261,563.777	1,000,000
1 Gpc	(3.085677581\times10^{22})	(2.062648062\times10^{14})	(3.261563777\times10^9)	(10^9)

The displayed values are rounded. The converter should retain greater precision internally and round only the final output.

Which Values Can Verify the Converter?

The following cases can be used to audit a converter implementation.

Test input	Expected conversion
1 km to m	exactly 1,000 m
1 international mile to km	exactly 1.609344 km
1 au to km	exactly 149,597,870.7 km
1 au to light-seconds	approximately 499.004783836 light-seconds
1 light-second to km	exactly 299,792.458 km
1 light-minute to light-seconds	exactly 60 light-seconds
1 light-hour to light-minutes	exactly 60 light-minutes
1 light-day to light-hours	exactly 24 light-hours
1 light-year to light-seconds	exactly 31,557,600 light-seconds
1 light-year to au	approximately 63,241.0770843 au
1 parsec to light-years	approximately 3.26156377717 ly
1 kiloparsec to parsecs	exactly 1,000 pc
1 megaparsec to parsecs	exactly 1,000,000 pc
1 gigaparsec to megaparsecs	exactly 1,000 Mpc

These extended values are intended for implementation testing. They do not imply that every user-entered distance is known to the same precision.

Back-Conversion Identity Test

A useful implementation check is to convert a value into another unit and then convert the result back into the original unit.

For an input (x):

[x\rightarrowy\rightarrowx']

A well-implemented converter should return:

[x'\approx x]

within its numerical and display precision.

For example:

[4.24\ \text{ly}\rightarrow1.29998990965\ \text{pc}\rightarrow4.24\ \text{ly}]

This test can reveal incorrect constants, reversed ratios, or premature rounding.

Worked Example 1: A Representative Earth–Moon Distance

Use a rounded representative Earth–Moon distance of:

[3.844\times10^5\ \text{km}]

For this example, the input is treated as having four significant figures.

Kilometers to Miles

[384{,}400\div1.609344]

[\approx238{,}855.0863\ \text{mi}]

Rounded to four significant figures:

[2.389\times10^5\ \text{mi}]

Kilometers to Astronomical Units

[384{,}400\div149{,}597{,}870.7]

[\approx0.00256955529\ \text{au}]

Rounded to four significant figures:

[0.002570\ \text{au}]

Kilometers to Light-Seconds

[384{,}400\div299{,}792.458]

[\approx1.282220382\ \text{light-seconds}]

Rounded to four significant figures:

[1.282\ \text{light-seconds}]

The same representative distance can therefore be written as approximately:

• (3.844\times10^5) km
• (2.389\times10^5) mi
• (0.002570) au
• (1.282) light-seconds
• (4.063\times10^{-8}) light-years

Every summary value uses four significant figures. The actual Earth–Moon distance varies, so this example demonstrates unit conversion rather than providing a live lunar range.

Worked Example 2: Converting 4.24 Light-Years

Suppose a source lists a stellar distance as:

[4.24\ \text{ly}]

Light-Years to Parsecs

[4.24\times0.3066013938]

[\approx1.29999\ \text{pc}]

Because the input has three significant figures, the appropriate displayed result is:

[1.30\ \text{pc}]

Light-Years to Astronomical Units

[4.24\times63{,}241.0770843]

[\approx268{,}142\ \text{au}]

Light-Years to Kilometers

[4.24\times9{,}460{,}730{,}472{,}580.8]

[\approx4.01135\times10^{13}\ \text{km}]

A precision-aware summary is:

• 4.24 light-years
• 1.30 parsecs
• approximately (2.68\times10^5) astronomical units
• approximately (4.01\times10^{13}) kilometers

Worked Example 3: Converting 2.637 Parsecs

Suppose a catalog gives:

[2.637\ \text{pc}]

Parsecs to Light-Years

[2.637\times3.261563777167]

[\approx8.60074368\ \text{ly}]

Rounded to four significant figures:

[8.601\ \text{ly}]

Parsecs to Kilometers

[2.637\times3.085677581491367\times10^{13}]

[\approx8.13693\times10^{13}\ \text{km}]

Rounded to four significant figures:

[8.137\times10^{13}\ \text{km}]

The parsec value may be preferable in an astrometric context, while the light-year value may be easier for a general audience to interpret.

Worked Example 4: Converting a Galactic-Scale Distance

Consider:

[8.2\ \text{kpc}]

First:

[8.2\ \text{kpc}8{,}200\ \text{pc}]

Then:

[8{,}200\times3.261563777167]

[\approx26{,}744.8\ \text{ly}]

With two significant figures:

[8.2\ \text{kpc}\approx27{,}000\ \text{ly}]

The same distance in kilometers is approximately:

[2.5\times10^{17}\ \text{km}]

Kilometers are mathematically valid, but kiloparsecs communicate the galactic scale more efficiently.

How Should Scientific Notation Be Used?

Scientific notation makes the order of magnitude visible without requiring a long string of digits.

Its standard form is:

[a\times10^n]

where:

[1\leq |a|<10]

For example:

[40{,}113{,}497{,}203{,}742.6\ \text{km}]

can be written as:

[4.01134972037426\times10^{13}\ \text{km}]

For user-facing output, the number would normally be rounded according to the source precision:

[4.01\times10^{13}\ \text{km}]

Recommended Display Pattern

For an extremely large value, show:

1. a rounded scientific-notation result
2. the equivalent astronomical unit
3. an optional higher-precision audit value

Example:

• Readable result: (3.09\times10^{19}) km
• Astronomical result: 1 Mpc
• Audit value: (3.085677581491367\times10^{19}) km

The audit value verifies the arithmetic. It does not imply that the original measured distance was known to 16 significant figures.

Does Conversion Change Measurement Accuracy?

No. Unit conversion does not improve the original measurement.

Suppose a distance is:

[100\pm2\ \text{pc}]

The relative uncertainty is:

[\frac{2}{100}0.02]or 2%.

Converting the central value to light-years gives:

[100\ \text{pc}\approx326.156\ \text{ly}]

The converted uncertainty is:

[2\ \text{pc}\approx6.523\ \text{ly}]

After appropriate rounding, the result can be reported as:

[326\pm7\ \text{ly}]

The relative uncertainty remains approximately 2%.

Linear Uncertainty Rule

For a linear conversion:

[y=kx]

where (k) is an exact conversion factor:

[\Delta y|k|\Delta x]

The relative uncertainty remains unchanged:

[\frac{\Delta y}{y}=\frac{\Delta x}{x}]

This applies when the conversion factor is exact and the source measurement supplies the relevant uncertainty.

What Is the Conversion Reliability Stack?

A trustworthy converted value depends on four separate layers.

Layer	Question to ask
Unit standard	Is the conversion factor defined or supported by an authoritative source?
Arithmetic	Was the correct ratio applied without premature rounding?
Input measurement	Does the original distance describe the intended object, observer, and time?
Display precision	Does the final rounding match the quality of the input?

The converter controls the first two layers and part of the fourth.

It cannot repair an outdated, uncertain, incorrectly labeled, or physically inappropriate source distance.

Why This Matters

A result may be mathematically correct but scientifically misleading.

For example, converting a planet’s mean orbital radius from astronomical units into kilometers is valid. Calling that result the planet’s current distance from Earth would be incorrect because the input describes a different path.

How Many Digits Should the Converter Show?

There is no universal decimal-place setting for all astronomical distances.

Use significant figures rather than a fixed number of digits after the decimal point.

Input	Suitable displayed conversion
4 ly	1 pc
4.2 ly	1.3 pc
4.24 ly	1.30 pc
4.2400 ly	1.3000 pc
exactly 1 au in a standards test	Extended digits may be shown

Trailing zeros can communicate precision. The values 4.24 and 4.2400 do not make the same precision claim.

Readable Result Versus Audit Result

For detailed work, provide two outputs:

• Readable result: rounded to the source precision
• Audit result: retained to higher numerical precision

Example:

• Readable result: 1.30 pc
• Audit result: 1.29998990965 pc

The audit result should be labeled clearly so users do not mistake calculator precision for measurement precision.

Can the Converter Find a Planet’s Current Distance?

No. Unit conversion alone cannot calculate the current separation between moving objects.

A current distance depends on:

• the target
• the observer
• the date and time
• the reference point
• the coordinate frame
• whether geometric or apparent position is intended

The official NASA/JPL Horizons system can produce date-specific observer ranges. Its system manual documents observer tables, range outputs, and light-time-corrected quantities.

After obtaining the appropriate range, use the astronomical distance converter to express that distance in another unit.

Can Redshift Be Converted Directly Into Megaparsecs?

No. Redshift is dimensionless and does not correspond to one unique distance through a fixed conversion factor.

Redshift is commonly written as:

[z\frac{\lambda_{\text{observed}}

\lambda_{\text{emitted}}}{\lambda_{\text{emitted}}}]

Converting redshift into distance requires a cosmological model and stated parameters.

Possible cosmological distance measures include:

• comoving distance
• proper distance
• luminosity distance
• angular-diameter distance
• light-travel distance
• lookback time

These quantities are not interchangeable.

NASA’s explanation of cosmological redshift describes how expanding space stretches light from distant galaxies.

Once a model has produced a specified distance in megaparsecs, the converter can change that distance into kilometers, light-years, or another length unit. It cannot decide which cosmological distance the redshift represents.

Common Conversion Errors and Result Differences

Problem	Likely cause	What to check
Result is about 1,000 times too large or small	A metric prefix was missed	Compare pc, kpc, Mpc, and Gpc
Result differs by about 1.609	Miles and kilometers were confused	Confirm the source unit
AU result differs slightly	A rounded AU value was used	Compare against exactly 149,597,870.7 km
Light-year result differs slightly	A different year convention was used	Check whether the converter uses a Julian year
Parsec result differs in later digits	One converter rounded its stored factor	Compare constants and display precision
Back-conversion does not recover the input	Intermediate values were rounded	Retain full precision until final display
Planetary distance differs substantially	The observer or date is different	Compare ephemeris settings
Galaxy distance differs	Different cosmological distance definitions were used	Compare the model and stated distance type
Result contains unsupported digits	Display rounding ignores input quality	Apply significant figures
Redshift was entered as a distance	Redshift is dimensionless	Calculate a named cosmological distance first
A light-year is treated as a duration	Distance and time units were confused	Use light-years for length and years for time
A value changes after repeated conversions	Displayed values were reused as inputs	Reuse the full-precision internal value

When two converters disagree, first confirm the input value and source unit. Then compare their stored definitions, rounding rules, year convention, and whether either tool performed an additional astronomical calculation rather than a pure unit conversion.

Astronomical Conversion Audit Checklist

Before publishing or relying on a converted distance, confirm:

• The input is a distance rather than a duration, angle, redshift, or velocity.
• The source unit is correctly identified.
• The target unit fits the scale and intended audience.
• Metric prefixes are interpreted correctly.
• The converter uses documented unit definitions.
• Intermediate calculations are not rounded prematurely.
• The displayed precision matches the input quality.
• The original distance describes the correct object, observer, and time.
• Cosmological distance types are not treated as interchangeable.
• The result includes an unambiguous unit label.

Practical Conclusion

Use the astronomical distance converter to express a known length in kilometers, miles, astronomical units, light-distance units, parsecs, or larger parsec multiples. The most reliable method is to normalize through meters, calculate with documented constants, retain precision internally, and round only the displayed result.

For solar-system work, astronomical units are usually the clearest choice. Light-seconds and light-minutes are useful when propagation scale matters. Light-years are intuitive for general descriptions of nearby stars, while parsecs align with astrometry and professional astronomy. Kiloparsecs, megaparsecs, and gigaparsecs keep galactic and extragalactic values readable.

A converter changes units. It does not determine a new orbit, improve a measurement, infer a distance from redshift, or replace specialist astronomical analysis.

Scope notice: This converter is intended for education, estimation, data presentation, and general scientific reference. Precision navigation, mission operations, astrometric inference, and cosmological analysis require validated specialist data and methods.

Related Space Distance and Scale Tools

• Light-Travel Time Calculator — convert a known path distance into one-way or round-trip vacuum propagation time.
• Astronomical Unit Converter — focus on conversions involving astronomical units, kilometers, and miles.
• Light-Year Converter — convert light-years into parsecs, astronomical units, and terrestrial units.
• Planet Distance Calculator — obtain or compare planetary distances for a selected observing context.
• Solar System Scale Calculator — turn large solar-system distances into proportional scale models.

Frequently Asked Questions

How Many Kilometers Are in One Astronomical Unit?

One astronomical unit is exactly:

[149{,}597{,}870.7\ \text{km}]

This defined unit does not change as Earth moves around the Sun.

How Many Light-Years Are in One Parsec, and Which Unit Is Larger?

One parsec is approximately:

[3.261563777\ \text{ly}]

A parsec is therefore larger than a light-year. Conversely:

[1\ \text{ly}\approx0.306601394\ \text{pc}]

For general presentation, one parsec is commonly rounded to 3.26 light-years.

Why Does the Converter Show More Digits Than My Input?

The calculator may retain high numerical precision when applying its conversion factors.

The extra digits can help audit the arithmetic, but the readable result should be rounded to match the significant figures of the source distance.

Can the Converter Calculate Distance From Stellar Parallax?

Not through unit conversion alone.

For an ideal positive parallax (p) measured in arcseconds, the familiar simplified relationship is:

[d_{\text{pc}}\frac{1}{p}]

Real astrometric analysis may require uncertainty treatment, zero-point corrections, and statistical inference, particularly when the parallax uncertainty is large.

Can the Converter Find a Planet’s Current Distance?

No. A current planetary distance depends on the target, observer, date, time, reference point, and ephemeris model.

Obtain the appropriate range from a source such as NASA/JPL Horizons, then use the converter to express that range in another unit.

Can the Converter Turn Redshift Into Light-Years?

Not directly.

A cosmological model must first convert the redshift into a specified distance, such as luminosity distance or comoving distance. The resulting length can then be converted into light-years.

Sources

1. Bureau International des Poids et Mesures — SI Base Unit: Metre
   Official SI definition fixing the speed of light in vacuum at exactly 299,792,458 m/s. Accessed August 1, 2026.

2. Bureau International des Poids et Mesures — SI Defining Constants
   Reference for the fixed numerical constants used to define the International System of Units. Accessed August 1, 2026.

3. International Astronomical Union — List of Resolutions
   Official archive containing the 2012 astronomical-unit resolution and the 2015 resolutions. Accessed August 1, 2026.

4. IAU 2015 Resolution B2 — Resolution Text and Supporting Paper
   Supporting publication reproducing and explaining the exact parsec relationship (648{,}000/\pi) astronomical units. Accessed August 1, 2026.

5. National Institute of Standards and Technology — Conversion Factors by Quantity
   Reference conversion factors for miles, light-years, parsecs, and other units. Accessed August 1, 2026.

6. NASA Science — Universe Glossary
   Reference explanations of parallax, parsecs, kiloparsecs, and megaparsecs. Accessed August 1, 2026.

7. European Space Agency — Measuring Stellar Distances by Parallax
   Explanation of annual stellar parallax and the astronomical-unit baseline. Accessed August 1, 2026.

8. NASA/JPL Solar System Dynamics — Horizons System
   Official ephemeris system for date-specific observer ranges and solar-system positions. Accessed August 1, 2026.

9. NASA/JPL Solar System Dynamics — Horizons System Manual
   Documentation for observer tables, range outputs, and light-time quantities. Accessed August 1, 2026.

10. NASA Science — Hubble Cosmological Redshift
    Explanation of cosmological redshift and expanding space. Accessed August 1, 2026.