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Photometry

Point Spread Function (PSF)

PSF stands for Point Spread Function which describes how an imaging system (ex. Telescope and CCD camera) image a singular point source such as a star. When a CCD image the object is divided into discrete point objects of varying intensity, each object is computed as a sum of the PSF of each point. The PSF is typically determined entirely by the imaging system and thus the entire image can be described by knowing the optical properties of the system. Understanding this, any CCD image can be studied through PSF applications.

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Flow of A Photometry Project

The video lesson assumes you have already reviewed the “Photometry an Overview”, “Comparison Stars”, and “Aperture Photometry” lessons. In this project, we’ll discuss the basic outline of a Photometry project from start to finish in order to put a global context to...

Calculating Magnitude

One of the capabilities of Photometry is to calculate magnitude of a given object. This is accomplished through Aperture Photometry. It is recommended that you have a good understanding of Aperture Photometry. Please review that lesson, if needed, before continuing.

APASS

The AAVSO Photometric All-Sky Survey (APASS) performed an allsky photometric survey in five filters: Johnson B and V, plus Sloan g′, r′, i′. The magnitudes range from 7th magnitude to about 17th magnitude. This catalog helps various research programs establish...

Aperture Photometry

When measuring the Flux (light) output of a star, there are a few methods to accomplish this. Two most common are: Aperture Photometry and Point Spread Function (PSF). This will focus on Aperture Photometry as it is the most accurate flux measurement, for non-crowded...

Photometry an Overview

The science of Photometry is the measurement of changes in Flux (light) from an object, or objects, to better understand the nature of what you’re observing. This could be a variable star, eclipsing binary star, Exoplanet, quasar, supernova, novae, blazar, or any...

Differential Photometry

Differential Photometry is comparing the difference between a target star and a comparison star. This is most usefulin Time Series observations. The direct comparison of a target and comparison star in the same field of view eliminates all other observationalvariables...

Landolt

In 1973, Landolt published a list of stars carefully transformed to the Johnson UBV system. He extended that list toinclude stars in the Cousins RC and IC bands in 1983. This was further refined in 1992. This includes fields near the celestial equator as well as...

Standard Photometric Stars

The central function of Photometry is accurate measurement of an object, typically a star, in terms of its brightness either overall magnitude/flux by dividing the flux into varying bands of the Electromagnetic Spectrum. Whatever your location is on the Earth, you use...

Extinction

In Astronomy, we tend to think of Extinction in terms of “Extinction Events”. However, there is another use of the term. In this case, extinction refers to the removal of light through an interaction with elements such as dust, gas, and atmosphere, or: The overall...

Counts

The term “counts” is very common in photometry, especially Aperture Photometry. Aperture photometry is used in differential photometry and absolute photometry. Counts focuses on all measured values within an aperture as opposed to focusing on data contained within a...