Variable Star Phase Screensaver
The Variable Star Phase screensaver shows real catalogue data for famous variable stars from AAVSO's key-less VSX API — type, period and epoch — used to compute where each star sits in its own brightness cycle right now. It's free, runs in your browser, and ESC exits.
Live preview
Press ESC to leave fullscreen. Settings are saved in your browser only.
How the Variable Star Phase screensaver works
The saver reads AAVSO VSX directly in your browser — no key and no account.
Real catalogue data for famous variable stars from AAVSO's key-less VSX API — type, period and epoch — used to compute where each star sits in its own brightness cycle right now..
It refreshes on a schedule, so what you see stays current.
Colours and the accent can be changed in settings; nothing is stored beyond your own browser.
Variable stars and the AAVSO catalogue
A variable star is one whose brightness changes over time. Some vary because they pulsate, like Cepheids and Mira stars, with periods ranging from days to hundreds of days. Others are eclipsing binaries, in which two stars orbit and periodically pass in front of each other. The American Association of Variable Star Observers, founded in 1911, coordinates and archives variable star observations made largely by amateur astronomers and makes them available to professional astronomers, researchers and educators.
Its International Variable Star Index, or VSX, is a catalogue of such objects with the type of variability, the period, and an epoch: a reference date, for many pulsators the date of maximum light. From a period and an epoch you can estimate where a periodic star is in its cycle at any moment by counting how many periods have elapsed since the epoch and keeping the fractional part, which is the phase.
That estimate has limits. Many variables are not perfectly regular, and the period of a Mira can change over time, as the AAVSO’s O−C diagrams of observed against predicted maxima show, so a computed phase can be well off for a star whose epoch is old. Phase shows where a star ought to be, not a measurement of its present brightness. For actual observations, the AAVSO light curves are the better source.
A worked example
Real catalogue data for famous variable stars from AAVSO's key-less VSX API — type, period and epoch — used to compute where each star sits in its own brightness cycle right now.
Settings & tips
- Accent and Background recolour the display.
- Data comes straight from AAVSO VSX in your browser.
- Press ESC to leave fullscreen.
Frequently asked questions
- Is this real data?
- Yes — it comes from AAVSO VSX and is refreshed on a schedule.
- Is a key needed?
- No. This source is fully key-less.
- Does it need an internet connection?
- Yes — it reads a live source, so it needs a connection to update.
- Is it free?
- Yes — free, no download, in your browser.
- What is the phase of a variable star?
- The fraction of its cycle completed since a reference moment, the epoch. Zero and one are the same point in the cycle, so it wraps around.
- Why can a computed phase be inaccurate?
- The period of some stars changes over time, and errors accumulate the further the current date is from the catalogue’s epoch.
- What kinds of stars vary?
- The AAVSO groups them by cause. Pulsating stars, whose radii swell and shrink, eruptive and cataclysmic stars, eclipsing binaries and rotating stars are among the main classes.