# Luminosity, Flux, Time: What Do They Mean?

• StephenPrivitera
In summary, the equation L=A[sig]T4 is used to determine the magnitude a telescope can reach based on its diameter and integration time. The equation f=L/A=[sig]T4 is used to find the magnitude a different telescope can reach based on the magnitude of the first telescope. Time comes into play when determining the magnitude a telescope can reach, and a telescope with a spectral resolution of 5 means it can differentiate between wavelengths with a difference of 5. The ratio of energy received by a telescope for stars with magnitudes 5 and 10 can be determined using the equation f=L/A=[sig]T4, and there are 3600 seconds in an hour.

#### StephenPrivitera

L=A[sig]T4
f=L/A=[sig]T4
Where does time come into these equations?

If one telescope of a known diameter can reach a certain magnitude, it is easy to find what magnitude a different telescope of known magnitude can reach. But if a telescope integrating over 10s can reach a certain magnitude, how can we determine what magnitude the same telescope will reach integrating over 1hr?

Also, what does it mean for something to have a spectral resolution of 5?

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Where does time come into these equations?
What are the units of [sig]?
But if a telescope integrating over 10s can reach a certain magnitude, how can we determine what magnitude the same telescope will reach integrating over 1hr?
Assuming you're still way above sky noise, presumably.
If one star has a magnitude of 5, and another 10, what is the ratio of the energy received, in unit time, by the same telescope?
How many seconds are there in an hour?

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## 1. What is luminosity?

Luminosity refers to the total amount of energy that a star or other astronomical object emits in a given amount of time. It is often measured in units of watts or solar luminosities.

## 2. How is luminosity different from flux?

Luminosity is a measure of the total amount of energy emitted by an object, while flux is a measure of the amount of energy received per unit area. In other words, luminosity is an intrinsic property of an object, while flux depends on the observer's distance from the object.

## 3. How is time related to luminosity and flux?

Time is an important factor in understanding both luminosity and flux. Luminosity can change over time as an object goes through different stages of its life cycle, while flux can also vary depending on the time of observation and the object's distance from the observer.

## 4. How are luminosity and flux used in astronomy?

Luminosity and flux are important tools in studying and understanding astronomical objects. They can provide information about an object's size, temperature, and distance. They also allow astronomers to compare and classify different objects in the universe.

## 5. How do scientists measure luminosity and flux?

Luminosity can be measured using various techniques, such as measuring the object's brightness at different wavelengths or analyzing its spectrum. Flux can be measured by using instruments such as telescopes and detectors to collect and measure the amount of energy received from an object.