Delta Cephei compared to the Sun

Yellow supergiant that swells and shrinks every 5.366 days; the star the Cepheids are named after, the stars used to measure the distances to other galaxies.

How big is Delta Cephei compared to the Sun?

Delta Cephei is roughly 44 times as wide as the Sun.

How much mass does Delta Cephei have compared to the Sun?

Delta Cephei has roughly four and a half times the mass of the Sun.

How hot is Delta Cephei compared to the Sun?

Delta Cephei’s surface is 5,632 °C. The Sun’s surface is 5,499 °C.

Worth knowing about Delta Cephei

You see Delta Cephei as it was about 940 years ago.

How much light it gives off: Mean luminosity 1,949 solar luminosities; visual magnitude runs 3.48 to 4.37 over a period of 5.366 days.
What it is: A yellow supergiant that does not sit still: it swells and shrinks, and gets hotter and cooler as it does.
How far away it is: About 940 light-years (about 290 parsecs).; How we know: Measured by parallax — Hubble’s of the star itself (Benedict et al. 2002), and now Gaia’s of the companion it travels with. It matters more here than for most stars: it is one of the handful of nearby Cepheids the period-luminosity relation is calibrated against, so its distance has to be known without using that relation. Rung 5 of the cosmic ladder — the distance to nearby stars
It is a rung of the cosmic ladder: The prototype classical Cepheid. The period-luminosity relation makes Cepheids standard candles, and they carry the distance ladder from rung 5 (parallax) out to other galaxies on rung 6.; How we know: Henrietta Leavitt noticed the rule in 1908 among the variable stars she was cataloguing in the Magellanic Clouds, and pinned it down in 1912 with 25 of them in one small galaxy, where they all sit at much the same distance — so the ones that pulsed slowest really were the brighter ones, and not just the nearer ones. Rung 6 of the cosmic ladder — the distance to other galaxies
Watch it change: It is one of the few stars that visibly does something. Look at the bottom corner of Cepheus on two nights, three days apart: at its brightest it nearly matches Zeta Cephei next door, and at its faintest it drops below Epsilon Cephei, on its other side. No telescope, no equipment, just your eyes and a bit of patience.
Its name and its story: Its variability was spotted in 1784 by John Goodricke, a deaf twenty-year-old in York who timed it by eye. He died at twenty-one, before anybody knew what he had found: nearly a hundred and thirty years later that beat became the ruler that measured the universe.

Delta Cephei — A model, seen from the Earth, with north up.

The numbers

Across	about 61 million km
Distance from us	about 940 light-years
Surface temperature	5,632 °C
Light given off	1,949 × the Sun

How anyone knows this

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Games it appears in

Show Delta Cephei in the model 🧭 Where is Delta Cephei?🕒 When can I see Delta Cephei?📖 How the Milky Way fits together 🌙 Plan an evening outside