Frequently Asked Questions
Everything you need to know about FITS Viewer.
What is a FITS file?
FITS (Flexible Image Transport System) is a standard data format used in astronomy for storing, transmitting, and processing scientific images. It is the most widely used format for astronomical images and data.
Is this FITS viewer free to use?
Yes, FITS Viewer is completely free with no account, no paywall, and no limits. You can open and explore as many FITS files as you like.
Do my files leave my browser?
No. All processing happens locally in your browser. Your FITS files are never uploaded to any server, ensuring complete privacy.
How do I open a FITS file?
You can open a FITS file by clicking "Open FITS file" on the landing page, or by dragging and dropping a .fits, .fit, or .fts file onto the upload area. You can also try the sample file included on the page.
What color maps are supported?
FITS Viewer includes 15+ color maps including Grayscale, Heat, Rainbow, Viridis, Magma, Inferno, Plasma, Cool, Spring, Summer, Autumn, Winter, Bone, and Copper.
Can I analyze the pixel values?
Yes. Use Probe mode to click on individual pixels to see their values, WCS coordinates (RA/Dec), and local 3×3 statistics. You can also draw regions to compute mean, sigma, and min/max over areas.
What stretch options are available?
Linear, Logarithmic, Square Root, and Arcsinh (asinh) stretches are available. You can also use preset percentile stretches like 99%, ZScale, Full, or set custom cuts.
What WCS coordinates does FITS Viewer support?
FITS Viewer reads WCS (World Coordinate System) headers from FITS files and displays RA and Dec coordinates as you move your cursor. Both degree and sexagesimal (HH:MM:SS) formats are supported.
Can I export images from FITS Viewer?
Yes. You can export the displayed image as PNG and region statistics as CSV.
What browsers are supported?
FITS Viewer works in all modern browsers including Chrome, Firefox, Safari, and Edge. We recommend using an up-to-date browser for the best experience.
Can I open multi-extension FITS files (HDUs)?
Yes. FITS Viewer supports multi-HDU FITS files. You can switch between HDUs using the selector in the toolbar.
Is there a file size limit?
There is no hard limit, but performance depends on your device's memory. Very large images (>200 MP) may be slow to process. All processing is done in-browser.