> For the complete documentation index, see [llms.txt](https://www.sunscan.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.sunscan.net/use/observe.md).

# Observe

{% embed url="<https://www.youtube.com/watch?v=u0lkpp-ddh0>" %}

A good session comes down to three things: the right time slot, a sharp and well-exposed spectrum, and a disk that crosses the slit from edge to edge. Since version 2.1, the scan assistant helps you with all three.

{% hint style="warning" %}
These features require firmware 2.1. The app offers the update as soon as it detects a SUNSCAN that needs it.
{% endhint %}

## Picking your time slot

The "Assist." button opens the scan assistant. Before the scan, it uses your GPS position and ephemeris data to give you:

* **Scan duration:** how long the disk will take to cross the slit.
* **Sun inclination:** the angle at which the disk meets the slit.
* **Quality of the observing window at this hour:** ideal, good, usable, strongly inclined…
* **Best time slot:** the part of the day to aim for.

The assistant also warns you when the Sun is below the horizon, and asks for your GPS position if it does not have it.

## Setting exposure and focus

The camera controls are covered in [Mobile app overview](/use/mobile-app-overview.md). Two settings matter before every scan.

In colour full-frame mode, the "AUTO EXP" button adjusts the exposure time for you. The setting is remembered, and the exposure is locked as soon as you start recording.

<figure><img src="https://3365769115-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fj8VBNLZ1OZic6lJdEMn0%2Fuploads%2F1Z9nZhRZlOWaByGO89lm%2Fsunscan-2-1-v07-autoexp.jpg?alt=media" alt=""><figcaption><p>AUTO EXP settles the exposure time on its own.</p></figcaption></figure>

The focus assistant has been rebuilt: a percentage bar of your best score, a curve of the last twenty seconds, a "New best!" flag and a reset button. The score is smoothed.

{% embed url="<https://3365769115-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fj8VBNLZ1OZic6lJdEMn0%2Fuploads%2FgVzcce5QUoq5DjcEGgjP%2Fsunscan-2-1-v09-focus-assistant-b.mp4?alt=media>" %}
The sharpness score rises as you adjust the focus.
{% endembed %}

## Knowing where you are in the spectrum

The "Ident." button runs spectral line identification. In full-frame mode, mono or colour, the app recognises which part of the spectrum is on screen, much like plate solving applied to a spectrum.

Line names are drawn straight onto the image, and the labels follow the zoom:

* **Solar lines:** in amber.
* **Telluric lines:** in blue.
* **Key lines:** in colour (Hα, Na D, Mg b, Ca II H & K…)

A banner gives the wavelength range, the dispersion (Å/px) and the number of lines identified. When it fails, the reason is spelled out: not enough light, saturation, focus…

<figure><img src="https://3365769115-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fj8VBNLZ1OZic6lJdEMn0%2Fuploads%2FXKFWab6JIzokiZaaBE7N%2Fsunscan-2-1-v06-ha.jpg?alt=media" alt=""><figcaption><p>The Hα region, with H₂O telluric lines in blue.</p></figcaption></figure>

## Placing the disk and starting the scan

{% stepper %}
{% step %}

### Bring the disk to the marker

The assistant guides you live as you position the disk along the slit, so that it stays centred for the whole crossing. Follow the prompts: "Bring the disk to the mark", then "In position, let the Sun drift off upstream, then record".

{% embed url="<https://3365769115-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fj8VBNLZ1OZic6lJdEMn0%2Fuploads%2FXZO3a0to0I19eYhQv0Gg%2Fsunscan-2-1-v03-scan-assistant-b.mp4?alt=media>" %}
From the observing window to the disk in position, the assistant walks you through the placement.
{% endembed %}
{% endstep %}

{% step %}

### Watch the recording

A gauge shows the time remaining and tells you when the disk has finished crossing. A live disk preview builds the disk column by column.

{% embed url="<https://3365769115-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fj8VBNLZ1OZic6lJdEMn0%2Fuploads%2F24DpTRF4tBpLXlD5OSaS%2Fsunscan-2-1-v04-live-disk.mp4?alt=media>" %}
The solar disk builds column by column while recording (video sped up ×2).
{% endembed %}
{% endstep %}

{% step %}

### Stop the scan

Stop the recording a few seconds after the disk has left the slit. That margin makes sure the edge of the Sun is fully in the scan.

If you forget, the automatic stop takes over: a 30 s countdown starts once the disk has finished crossing, then the recording stops by itself. Tap the countdown to cancel it. It is on by default and can be turned off in the Settings.

<figure><img src="https://3365769115-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fj8VBNLZ1OZic6lJdEMn0%2Fuploads%2FTerYgYAIdVlm5U9zJcmU%2Fsunscan-2-1-v04-rec.jpg?alt=media" alt=""><figcaption><p>The automatic stop countdown, below the live disk preview thumbnail.</p></figcaption></figure>
{% endstep %}
{% endstepper %}

## After the scan

The "Scan complete" dialog has been redesigned: you pick the observed spectral line from a grid of coloured pills. That tag drives the watermark, the gallery filters and the Hε images of a Ca II H scan.

The scan then lands in the gallery, where you can process it, stack it or animate it, and then [retrieve your data](/use/retrieve-your-data.md) on your computer.

{% hint style="danger" %}
Never look at the Sun directly, or through an instrument, without proper protective equipment. You observe with the SUNSCAN on your phone screen.
{% endhint %}

## Going further

* [The sun in Hα](/use/observe/markdown.md): the most observed line.
* [Reference Cards](/use/observe/images-and-media.md): field landmarks.
* [Colored sun spectrum](/use/observe/interactive-blocks.md): finding your way among the lines.