What is SS Cygni?

Close binary where a white dwarf siphons gas from a companion, flaring up every few weeks.

Worth knowing about SS Cygni

You see SS Cygni as it was 368 years ago.

Why it stands out

Normally magnitude 12, it brightens to magnitude 8 in outburst, and amateurs have watched it every night since 1896.

What it is

Each outburst is the disc of gas round the white dwarf suddenly heating up and brightening.

How we know: Over a century of brightness records show a repeating outburst pattern; spectroscopy shows gas streaming onto the smaller, hotter star.

How anyone knows this

• Why some stars change brightness
• How a star is born, and the ways it can end
• Every kind of object on this site

Also worth a look

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