Earendel

The name

The most distant star ever seen needed a lens the size of a galaxy cluster.

Back in 2022, Hubble spotted a point of light that had set off on its journey 12.9 billion years earlier; a single star sitting at the very edge of the observable universe. They called it Earendel, Old English for morning star. On its own it's far too faint to see. The only reason it shows up at all is that a cluster of galaxies happens to sit in front of it, bending spacetime into a magnifying lens.

Your telescope's raw frames are full of light too faint to see. Earendel is the lens.

One · Before the case is open

Most of a night is decided indoors.

Earendel opens on Tonight. It works with the telescope still in its box, which is the half of the hobby no app bothers with.

Is tonight a night?

The forecast for your garden, not your county: cloud, transparency, and the hour the dew is due. It will tell you plainly when the answer is no, which saves you the setup and the disappointment both.

What to point at

Three thousand targets ranked for tonight, from where you actually stand: what has risen, what clears the roof, what fits the lens you own, and what the Moon is about to ruin. Not an atlas to get lost in; a shortlist, with the reasoning shown.

The nights you'd otherwise miss

Everyone knows an eclipse is coming. Nobody knows the space station crosses the face of the Sun over their own garden a fortnight on Thursday. Earendel works out both, draws the corridor the crossing is visible from, and counts you down with the exposure already set for something moving that fast.

Carry on with what you started

Two hours on the Whirlpool last month is an asset, not history. Tonight offers to add to it, and matches the target however it was spelled the first time, which is the reason most apps lose track of it.

How dark your garden really is

Not a colour off a light-pollution map drawn for a postcode. Earendel measures the sky between the stars of your own frames against the catalogue, in magnitudes per square arcsecond, and plans by that number instead. It refuses to guess when a frame can't answer honestly.

Guided from the first click

No manual, no wandering the UI. Earendel walks you from first connection to first finished image, with sensible defaults doing the thinking.

Two · While it runs

You should be able to go inside.

Set the night up, shut the door, and let the Mac do the watching. It knows the difference between a night going wrong and a night that has simply finished.

Focus you can check

The commonest complaint in the hobby is auto-focus reporting success while the scope sits miles out. Earendel runs the telescope's autofocus, then measures the stars instead of trusting the word “success”. It compares them with how tonight looked when focus was genuinely good and allows for the fact that a target low in the sky is blurred by air rather than by the focuser.

Watches the weather with a camera

Your scope has two lenses and uses one. Earendel reads the idle finder as a cloud sensor, so cloud is seen coming in from one side before it reaches what you're shooting, and a rising Moon is told apart from an incoming bank. Best of it: stars fading on the imaging lens while the finder still sees them is dew on the glass, not cloud. And dew is a night you can rescue with a towel.

Says why the frames are going

Frames dropping is a symptom. Earendel names the cause while the night can still be saved: wind, dew, cloud overhead, a target sinking into the murk, the wrong filter left on the wheel. Then it says whether to fix it, move on, or call it a night.

Knows the night will fit

Before a frame is taken it works out whether the card, the battery and the space on your Mac get you to sunrise, and says so while there is still time to do something about it. It ends a run deliberately rather than letting the card fill up mid-galaxy.

In the menu bar, all evening

Frames, integration, and how the sky is behaving, in the corner of the screen you're already using. A notification when the night is done, because by then you're indoors, and one press turns the finished night into a picture.

Mission control

Both lenses live on the screen already on your desk, full resolution, with 1×, 2× and 4× and a sky you can drag. Pick a target and plate-solved GoTo puts it in frame. The tele lens's footprint is drawn on the wide view, so you can see what you're about to photograph before you commit the night to it.

Daylight plans too

Earendel calculates eclipses and satellite crossings for where you actually stand, then maps the narrow path where a solar or lunar transit is visible. Filtered-Sun telescope control remains an attended TestFlight field beta until its physical safety session passes.

Local. Always.

No cloud round-trip, no upload failed, no waiting on someone else's server to see your own photograph. Nothing leaves your Mac, and nothing needs to arrive: the two and a half million stars Earendel measures your colour against travel inside the app. Works on a hilltop with no signal, and will still work when someone else's API is retired.

Three · The Forge

Everything your phone app does, on a screen that deserves it. Then everything it can't.

Frame rescue

The phone app bins frames at the first wobble, sometimes half the night's worth. Earendel re-examines every sub, keeps what's sharp, and shows you exactly what it saved.

The Forge

Metal-accelerated stacking on Apple Silicon handles the lot: registration, sigma-clipped integration, stretch and background extraction, tuned to your scope's sensor. No tutorials, no scripts, no first step to fail.

Colour measured, not assumed

Every other tool balances colour by hoping the average star in your frame is grey. It never quite is; it depends which stars are in shot and how much dust sits in front of them. Earendel matches your field to the Tycho-2 catalogue, two and a half million stars carried inside the app, and takes the colour from stars whose real colours were measured from orbit. On a recent M 31: 324 stars matched, and the usual assumption was out by fifteen per cent.

Four looks, or six sliders

Natural, Vivid, Deep, Soft. One tap each, and every setting inside them was chosen together on real data. Turning the colour up without holding the noise down is how a picture ends up looking cheap. The sliders are underneath for the nights you want them, and nothing you touch costs a restack.

Knows when to leave it alone

Drizzle only helps when your pixels are too coarse for the detail that arrived. Ask for it on data that is already finely sampled and Earendel measures the stars, declines, and tells you why, rather than spending an hour of your evening making the picture softer.

Stack across nights

Three clear nights on one galaxy become a single deep master. Different scopes register too: a friend's DWARF Mini frames fold straight into your DWARF 3 stack. Owners have asked the vendors for this for years; the answer is always soon.

Sessions that sort themselves

Frames import over Wi-Fi and organise by target and night. Thumbnail clutter cleaned up, formats kept sane. No SD cards, no mysteriously empty folders. Hold a picture down to see what the telescope made of the very same night.

Properly native

SwiftUI, sandboxed, and built for the Mac App Store. Not a port or a webview, and no phone app stretched into a window.

Why it matters

Your scope caught more than it kept.

The stack your telescope builds on board is made for a phone screen; it has to be quick and small, and done before you're back indoors. Getting there means throwing signal away. The raw frames it saved at the same time, the FITS files, still hold the faint arms, the outer shells and the dust.

The board inside your scope hasn't a patch on your Mac for raw computing power, and Earendel puts every bit of it to work on those frames. Same telescope, same night, more galaxy.

The app will be free to download, and the free app stays useful: the whole of Tonight, DWARF 3 control, and the whole pipeline. The Forge unlocks for a one-off £24.99, less than an eyepiece, and £19.99 in launch month. No subscription, no cloud account, nothing recurring.

EARENDEL