AstroKids › Everything in the sky › SS Cygni
cataclysmic variable · binary star system

SS Cygni

Most stars look the same night after night, but this one suddenly gets a hundred times brighter every few weeks and then fades again — you could watch it change with a small telescope! It is two stars, one stealing gas from the other.

🕒 When can I see it?🚀 Travel there
SS Cygni — Drawn, not photographed.

What it is

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

Cataclysmic variable: A white dwarf stealing gas from a neighbour, flaring as it lands. Every kind of thing there is →

How to find SS Cygni

Look in the constellation Cygnus.

Too far north to rise for most of the Southern Hemisphere.

The Planetarium works out where it actually is from your own place and the date — including whether it is above the horizon at all tonight.

Show me SS Cygni in tonight's sky

What you will really see

With binoculars

Binoculars find it, especially braced against a wall or a fence — it stays a point of light, but now you know which point.

Through a small telescope, on a good night

A faint star that suddenly flares up — catching one in outburst is the sport.

🔭 See it drawn as it looks through a telescope
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🖨️ Print a sheet and go and look
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Worth knowing about SS Cygni

On the 100-meter-track scale model of the Milky Way, SS Cygni would be about 37 centimeters from the Sun — roughly the length of an adult's forearm. Light takes 370 Earth years to get here from SS Cygni, so what you are looking at is SS Cygni as it was 370 Earth years ago.

What it is made of
A close binary pair — a white dwarf siphoning gas off a companion star, which piles up and ignites, flaring every few weeks.
How we know: Over a century of brightness records show a repeating outburst pattern; spectroscopy shows gas streaming onto the smaller, hotter star.
What makes it worth knowing
Normally magnitude 12, brightens to magnitude 8 during outbursts. Observed continuously since the 1890s.
The numbers
Distance from us~370 light-years

How anyone knows this

Nobody flew a tape measure out there. Every number on this page was worked out from the ground:

Next to it

The Milky Wayspiral galaxyNaked eyeProxima CentauristarWith effortAlpha Centauri A & Bbinary star systemNaked eyeSiriusstarNaked eyeVegastarNaked eyeArcturusstarNaked eye
📖 How the Milky Way fits together

Then go outside

Clear tonight? The Planetarium will show you what is worth a look. Then just go out.

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