FAQ

How sunlight, twilight, and your body clock fit together — and how Solar Rhythm uses that. Lifestyle education only. Not medical advice.

Also see the user manual.

The big idea

What is a “solar rhythm”?

Your body runs on a roughly 24-hour circadian clock. The strongest daily reset signal for that clock is light, especially the changing pattern of natural light from night → dawn → day → dusk → night again.

Solar Rhythm turns your location into a personal clock of those solar moments (dawn, sunrise, noon, sunset, dusk, and related times) so you can plan wake, outdoor light, activity, and wind-down relative to your sky — not a fixed city schedule.

Why not just use clock time (e.g. “wake at 6:30”)?

Clock time is the same everywhere; sunlight is not. Sunrise in June vs December, or in Perth vs London, can differ by hours. Aligning routines to solar events tracks the light environment your circadian system actually senses.

Is this medical treatment?

No. Solar Rhythm provides lifestyle guidance only. It does not diagnose, treat, or prevent any condition. If you have sleep, mood, or eye-health concerns, talk to a qualified clinician.

Light, the eye, and the clock

How does light affect the circadian clock?

Special cells in the retina (ipRGCs) detect light intensity and spectrum and signal the brain’s master clock (the SCN in the hypothalamus). Enough of the right light at the right time can:

• Suppress melatonin and raise alertness
• Help set (phase-shift) when you feel sleepy or awake
• Support the morning cortisol awakening pattern when dawn light arrives

Dim evening light (or avoiding bright indoor light after dusk) helps melatonin rise — often discussed as dim-light melatonin onset (DLMO).

What is melatonin?

Melatonin is a hormone that rises in darkness and helps signal “biological night.” Bright light — especially earlier in the day — tends to suppress it and promote wakefulness. Solar Rhythm does not measure melatonin; it only surfaces solar times you can use as lifestyle cues.

Daylight and twilight

What is daylight vs twilight?

Daylight usually means the Sun’s disk is above the horizon (sunrise → sunset). Useful outdoor light does not start and stop exactly then — the atmosphere still scatters sunlight when the Sun is below the horizon. That transition is twilight.

Twilight is split by how far the centre of the Sun sits below the horizon:

• Civil — 0° to 6° below
• Nautical — 6° to 12° below
• Astronomical — 12° to 18° below
• Night — more than 18° below (for illumination purposes)

What do the Solar Rhythm times mean biologically?

Approximate lifestyle framing (not a clinical protocol):

• Solar midnight (nadir) — Deep night proxy; typically near minimum core temperature and high melatonin expression.
• Astronomical dawn — Negligible circadian stimulus; still below the threshold that strongly drives ipRGCs / the SCN.
• Nautical dawn — Minimal light; may matter for vision, but usually weak for phase-shifting the clock.
• Civil dawn — Often crosses a practical outdoor-light threshold linked with waking, reducing sleep inertia, and beginning melatonin suppression.
• Sunrise → solar noon → sunset — Daylight / peak alertness window; full SCN drive toward wakefulness when outdoor light is available.
• Civil dusk — Light falling fast; a cue that night is coming. Keeping evenings dimmer can support melatonin onset.
• Nautical / astronomical dusk — Functionally dark for many circadian purposes; melatonin synthesis proceeds if you are not flooded with indoor light.

Photography-oriented times (golden hour, sunrise end, sunset start) are geometric sun-altitude markers; they are optional in Settings.

Why does twilight length change with season and latitude?

Near the equator the Sun dives steeply below the horizon, so twilight is short. At higher latitudes the Sun skims more shallowly, so twilight can last much longer — and in polar summer/winter some events may not occur for parts of the year.

Using the app

How does Solar Rhythm calculate times?

It uses your latitude/longitude and the open-source SunCalc library to compute solar geometry for each local day. No weather API is required for the clock itself.

Which times should I enable in Settings?

Defaults focus on the most useful lifestyle anchors: civil dawn, sunrise, solar noon, sunset, civil dusk.

Add nautical/astronomical times if you want finer twilight detail, solar midnight for a “deep night” marker, or golden-hour times for photography. Enable only what you will actually act on — more cues can mean more noise.

What are Export / Mark / Cancel for?

• Export week / Export day — create a calendar file (.ics) for your phone calendar.
• Mark all / On calendar — records in the app that you added those cues. This does not change your phone calendar by itself.
• Cancel day / Cancel week — build a cancel .ics for times you marked, so you can try to remove matching events from your calendar app. Some calendar apps ignore cancels; you may need to delete manually.

Does my data leave the phone?

Preferences, On calendar marks, and export records stay in browser localStorage. Location is used on-device for solar math. Suburb lookup may send coordinates to a geocoding service (via the site’s proxy when available). There is no Solar Rhythm account or cloud profile.

Practical starter routine

1. Get outdoor light soon after civil dawn → sunrise when you can.
2. Use the solar noon window for demanding work or exercise if it fits your life.
3. After sunset / civil dusk, dim screens and overheads where practical.
4. Keep a stable sleep target and let solar cues shift gently with the seasons.

Notes

Twilight definitions follow the standard geometric stages used in solar astronomy (civil / nautical / astronomical). Circadian notes are educational summaries of commonly discussed light–biology relationships, not personalised medical guidance.