ATRONOMY – ATROPHOTOGRAPHY & IMAGING (40) CALCULATOR
Star Fwhm Pixels
A precise tool.
What is the Star Fwhm Pixels & How does it work?
In astronomical imaging the apparent size of a point source, such as a star, is broadened by atmospheric turbulence. This effect is quantified as the “seeing” and is expressed in arcseconds (arcsec). Better atmospheric conditions yield smaller seeing values, resulting in sharper stellar images. The detector records the image on a pixel grid, and each pixel subtends a certain angular size on the sky, known as the pixel scale (arcsec/pixel). The pixel scale depends on the telescope’s focal length and the physical size of the detector’s pixels. Combining these two quantities allows us to predict the star’s full‑width‑half‑maximum (FWHM) measured in pixels. This is essential for assessing image quality, planning exposure times, and optimizing post‑processing algorithms.
FWHM_{pix} = frac{text{Seeing} (arcsec)}{text{Scale} (arcsec/pixel)}
FWHM_{pix} = star FWHM in pixels
Parameters
Result
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Frequently Asked Questions
What is FWHM in astronomy?
FWHM stands for Full Width at Half Maximum. It measures the width of a peak in a spectrum or an image where the intensity drops to half its maximum value.
How does pixel scale affect FWHM calculation?
The pixel scale, which is the angular size each pixel subtends on the sky (in arcseconds per pixel), directly affects the FWHM calculation. A higher pixel scale means each pixel represents a larger area of the sky.
Why is atmospheric seeing important in astronomy?
Atmospheric seeing refers to the blurring effect on star images caused by Earth’s atmosphere. It impacts the resolution and sharpness of astronomical observations, with better conditions leading to sharper images.
How do I calculate FWHM from arcseconds?
To calculate FWHM in pixels, divide the FWHM in arcseconds by the pixel scale (arcseconds per pixel). This gives you the width of the star’s image in terms of pixels.
What does a smaller FWHM value indicate?
A smaller FWHM value indicates better resolution and sharper images, which is desirable for detailed astronomical observations.
How can I improve the FWHM of my star images?
Improving atmospheric conditions, using a telescope with a higher focal length, or employing adaptive optics can help reduce FWHM and enhance image sharpness.
Is there a relationship between pixel scale and telescope magnification?
Yes, the pixel scale is inversely related to the telescope’s focal length. A longer focal length results in a smaller pixel scale, meaning each pixel represents a smaller area of the sky.
Results are for informational purposes only and do not constitute professional advice.