When to use this calculator
Convert an astronomical flux ratio into a magnitude difference. A brighter first source has a lower magnitude and therefore a negative difference.
Explore the astronomical distance calculators for other questions in this topic. For a related calculation, use the Magnitude Flux Ratio Calculator: Compare received flux from a difference in astronomical magnitudes.
PUTTING IT INTO PRACTICE
Magnitude Difference From Flux: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| First-to-second flux ratio | 100 |
| Result | -5 magnitudes |
- Check the input labels and enter the example values above.
- Apply the relationship: First magnitude − second magnitude = −2.5 log₁₀(flux ratio).
- The result is -5 magnitudes, rounded for display.
How to interpret your result
A brighter first source has a lower magnitude and therefore a negative difference.
A light-time calculation uses vacuum propagation speed. Parallax angle must use the stated angular unit. Simple inverse-parallax estimates can be unreliable when measurement uncertainty is large relative to the parallax.
Frequently asked questions
Are a parsec and a light-year the same unit?
No. Both measure astronomical distance but use different definitions. A parsec is defined through the parallax relationship.
When is the magnitude difference from flux calculator useful?
Convert an astronomical flux ratio into a magnitude difference. A brighter first source has a lower magnitude and therefore a negative difference.
How do I use the magnitude difference from flux calculator?
Enter first-to-second flux ratio. The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
First magnitude − second magnitude = −2.5 log₁₀(flux ratio).
What should I check before using the result?
A brighter first source has a lower magnitude and therefore a negative difference.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
Further reading
For background on this topic, see OpenStax: stellar distances and parallax ↗. This is a topic reference, not an external review or endorsement of this tool.
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