HD 220445

HD 220445 is a K0 orange star in the constellation Andromeda, 103.5 ly from Earth, shining at apparent magnitude 8.61 (V). It is catalogued as HIP 115470.

WHAT IT IS

Orange star

HOW FAR

103.5 ly

The light arriving now left it that long ago.

HOW BRIGHT (V)

8.61

Binoculars reach it; the naked eye does not.

WHERE TO LOOK

Andromeda

The patch of sky it sits in, as seen from Earth.

What it takes to see HD 220445 for yourself. Everything in this part of the page is worked out for a real horizon, a real night and the equipment you say you have.

A star gives out light at every wavelength at once. The dark gaps are atoms in the thin gas above its surface, each one removing the single colour it is able to absorb — which is how a list of ingredients is read off something nobody will ever touch.

• HEAVY ELEMENTS The catalogued iron figure for HD 220445 is +0.02, which puts it at about the Sun's share of the elements heavier than helium. The figure is a logarithm: nought is the Sun, and every whole step is a factor of ten. It comes from published measurements of the star itself, not from the spectrum above — which belongs to the type.

Pickles (1998) stellar spectral flux library. K0 V — the average of several real stars of this type, not an observation of any one star. Sampled every 5 angstroms; 1,895 points rebinned onto 1,024 log-spaced display points and normalised to the median flux. Brightness is scaled to this spectrum’s own middle value, so the shape is the measurement and the height is not. The 7 lines named above are the ones that stand clear of the scatter and of the features around them; a spectrum at this sampling holds many more that it cannot separate. The samples themselves, as JSON, CSV or VOTable.

HD 220445 is an orange star on the main sequence, fusing hydrogen in its core — about ten billion years of it in all — and when that hydrogen is gone it will swell into a red giant, and end as a white dwarf.

NOW Hydrogen fuses to helium in the core, and the outward push of that exactly balances the star's own weight. This is the long, steady stretch — nine-tenths of a star's life — and it ends when the core's hydrogen is gone.

NEXT With the core out of hydrogen, the star swells enormously and its surface cools to red. It burns helium in the core and hydrogen in a shell around it, and it loses mass from its surface the whole time.

• HOW FIRM No luminosity class is recorded for this star — the catalogue gives its temperature class and stops there — so which stage it is in was read from how far its brightness sits above where a star of its temperature would sit on the main sequence. That is a best estimate rather than a classification.
• ALSO No mass has been measured for this star. The figure above is inferred from its temperature by way of the main-sequence relation between the two, which is tight enough to be worth stating and is still an inference.

Which stage HD 220445 is in was read from its catalogued class, its temperature and its total output at every wavelength — not from its brightness in visible light alone, which understates a cool star by a factor of several. The mass it started with is about the Sun's own mass, from its temperature, and that mass is what chooses the track. Every span of time here comes from the standard relation between a star’s mass and how long its fuel lasts, and is rounded to a single figure: they are orders of magnitude and none of them is a date.

The raw catalogue values, as the source published them, with the error bars where one was published — sorted by what each set of figures is about rather than by the order they happened to be stored in.

• HD HD 220445
• HIP HIP 115470