# Chi Cygni (χ Cyg)

Chi Cygni (χ Cyg) is a star in the constellation Cygnus, magnitude 8.0.

**A star whose brightness can swing more than ten-thousand-fold — one of the widest ranges of any pulsating star.**

In 1686 the German astronomer Gottfried Kirch was searching that part of the sky for observations of Nova Vulpeculae when he noticed that a star marked on Bayer’s atlas, Chi Cygni, was missing. He kept watching, and on 19 October 1686 it reappeared at 5th magnitude. He had found one of the most extreme [variable stars](https://astropilot.space/glossary/variable-star) in the sky.

At its extremes Chi Cygni has climbed to magnitude 3.3 and sunk to 14.2, over cycles of about 409 days — yet its total energy output changes far less. It is a pulsating red giant near the end of its life, swelling from about 350 to 480 times the Sun’s radius. As it cools, molecules form that soak up visible light, and more of its glow shifts into the infrared.

It is also an S-type star, its spectrum marked by zirconium oxide and by technetium — an element with no stable form, which must have been forged inside the star itself. And it was the first Mira variable in which a magnetic field was detected.

Chi Cygni (χ Cyg) is 590 light-years away: the light we see from it set off around 1435, around the time Gutenberg printed his Bible.

## Did you know?

- **Brightest in a century.** Its 2006 maximum reached magnitude 3.8, the brightest for over a century. Less than ten years later, the 2015 maximum barely reached 6.5 — perhaps the faintest ever seen.
- **A star that went missing.** Flamsteed catalogued a star as Bayer’s Chi Cygni when Chi was probably too faint to see, so he had in fact recorded another star. Nobody noticed until 1816.
- **Weighed by its own pulse.** By measuring how fast layers of its atmosphere rise and fall, astronomers weighed Chi Cygni at about 2.1 times the Sun’s mass.

On the Swan’s long neck between Sadr and Albireo, a little south-west of Eta Cygni. Near maximum it can reach naked-eye visibility; months later it drops below 13th magnitude. Check it every few weeks and watch its red deepen as it fades.

## When and where to see it

It is best placed in the evening sky around August, when it crosses the meridian at about 10 pm local time (around midnight in July). It can be seen from everywhere north of 57°S and never sets north of 57°N.

At its highest it stands 73° up from 50°N, 88° up from 35°N, 57° up from the equator, 22° up from 35°S.

## Facts

- Type: Star
- Constellation: Cygnus
- Designations: χ Cyg, HR 7564, HD 187796, HIP 97629
- Magnitude: 8.0
- Position: RA 19h 50.6m, Dec +32° 55′ (J2000)
- Spectral type: S6-9/1-2e
- Colour: orange-red (B−V 1.82)
- Brightness: varies from magnitude 3.3 to 14.2
- Distance: 590 light-years
- Discovered: Gottfried Kirch, 1686, Discoverer of its variability

Open AstroPilot to see when Chi Cygni (χ Cyg) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view. https://astropilot.space/object/chi-cygni