The cosmic odometer and camera framing

Two smaller tools round off Skyfold: the Cosmic odometer tab and the Camera framing dialog in the Sky tab.

The cosmic odometer

Open Cosmic odometer and enter Start date and Start time — your birth, for example. The end is the date in the side panel; press Now there to measure up to today. Your latitude comes from the place in the side panel.

Four cards show the distance travelled, each with its speed:

• Earth rotation at your latitude — the circle your place draws around the Earth's axis every sidereal day (about 0.29 km/s in Central Europe, 0.47 km/s at the equator).
• Earth around the Sun — the real path length of the Earth's orbit, added up from the planetary theory: about 940 million km per year.
• Sun around the centre of the Milky Way — 247 km/s (Reid and colleagues, 2019).
• Solar system relative to the cosmic background radiation — 369.82 km/s (Planck 2018).

These motions are measured against different reference points, so Skyfold lists them separately instead of adding them into one big number.

Below the cards you find the number of Days, Orbits of the Sun, Full Moons and Earth rotations (sidereal). The table Stars whose light left them when you started lists naked-eye stars whose distance in light years matches your span of years: the light you see from them tonight set off around your start date.

The Solar system walk scales the Sun to a 20 cm ball and tells you how far away and how big each planet would be today — a good outdoor activity with children.

The start date stays in this browser: it is saved with the project but never put into share links.

Camera framing

In the Sky tab, press Camera framing…. Choose a Target (the Moon, a planet or a bright star), the Focal length (mm) of your lens and your Camera sensor. Skyfold draws a finder chart around the target, north up and east left, with the field of view as an orange rectangle and the Moon or planet at its true apparent size.

Use it to decide whether a lens frames the whole Moon with some margin (about 1 000 mm on a full-frame camera) or whether the Pleiades fit (around 300 mm).

Download PNG saves the chart. If Lumina is available, Open in Lumina hands the chart over to Lumina, where the Astro Lab stacks and stretches the frames you take.

Where to go from here

• Help → About the accuracy summarises the algorithms and data sources.
• Every calculation is also available as an API and MCP tool, for example the planet positions and the eclipse circumstances, so assistants and scripts get exactly the same numbers as the app.
• Go back to your sky in five minutes for the basics.