# APT Darkness Clock — Knowing when to image/observe

> Calculates optimal deep sky astrophotography and observation times. (iPhone/iPad app by Ivaylo Stoynov.)

- Source: https://appshunter.io/ios/app/apt-darkness-clock/id1351332907 (this page in markdown: same URL + `.md`)
- Developer: [Ivaylo Stoynov](https://appshunter.io/developer/1351332906)
- Category: Reference, Utilities
- Price: Free
- Rating: 5.00/5 from 4 App Store ratings · 3 written reviews indexed
- Age rating: 4+
- Requires: iOS 10.0 · 1 MB
- Languages: American English
- Released: 2018-02-24
- Data updated: 2026-06-01
- Monetization: free
- User reviews in markdown: https://appshunter.io/ios/app/apt-darkness-clock/id1351332907/reviews.md

## What is APT Darkness Clock?

APT Darkness Clock (APT DC) is a free app without ads, that calculates the suitable time for deep sky astrophotography or observing in selected night and location. It is a small sub-set of a full featured desktop application named APT - Astro Photography Tool.

APT is like Swiss army knife for your astro imaging sessions. No matter what are imaging with - Canon EOS, Nikon, CCD or CMOS astro camera, APT has the right tool for planning, collimating, aligning, focusing, framing, plate-solving, controlling, imaging, synchronizing, scheduling, analyzing, monitoring and more. You can find additional information about APT at www.astroplace.net.

To image or observe a faint deep sky objects is needed to use the darkest time of the night. This is the time between the evening astro twilight end, the morning astro twilight beginning and when the Moon is below the horizon. In APT that time is named DSD Time - Deep Sky Darkness Time. 

The purpose of APT DC is to calculate what is the DSD Time duration and when this time starts/ends for selected night and location. It is possible to use the current location or one of three other stored observing sites.   

For suggestions and support related to APT DC, use the dedicated section of the APT Forum at - http://aptforum.com/phpbb/viewforum.php?f=26

## Key features

- Calculates Deep Sky Darkness Time (DSD Time)
- Determines start and end times for DSD Time
- Calculates DSD Time duration
- Supports current location
- Allows storing up to three observing sites
- Free and ad-free

## Recent user reviews (3 of 3)

All indexed reviews: https://appshunter.io/ios/app/apt-darkness-clock/id1351332907/reviews.md

### 5/5 — Handy app

*2018-05-03, version 1.3*

Handy app from apt , lets you know sun rise /set, Astro twilight start end /moon rise/set /illumination all handy in one place what’s not to like .

### 5/5 — Simple handy App

*2018-05-02, version 1.3*

Nice simple easy to use App

### 5/5 — Good app!

*2018-04-13, version 1.3*

Handy info to have to hand!  Works
Well to make more accessible the info I’ve been using in APT for several years!

## Frequently asked questions about APT Darkness Clock

### What is APT Darkness Clock used for?

APT Darkness Clock is used to calculate the optimal times for deep sky astrophotography and observing. It specifically determines the Deep Sky Darkness Time (DSD Time), which is the period between evening and morning astronomical twilight when the Moon is below the horizon.

### Is APT Darkness Clock free to use?

Yes, APT Darkness Clock is a free application. It does not contain any advertisements or in-app purchases, making it completely free for users.

### What devices does APT Darkness Clock support?

APT Darkness Clock is available for iOS devices, including iPhones and iPads. It is designed to run on these platforms to assist users with their astronomical observations.

### How accurate is APT Darkness Clock?

The app calculates optimal times based on astronomical twilight and moon phase, which are scientifically determined. Users can select their current location or stored sites for precise calculations relevant to their observing environment.

### Can I use APT Darkness Clock offline?

The provided information does not specify offline functionality. However, as it calculates times based on location and astronomical data, an internet connection might be required for initial setup or location services.

### What is the age rating for APT Darkness Clock?

APT Darkness Clock has an age rating of 4+. This indicates it is suitable for users of all ages and does not contain any content that would restrict its use by younger audiences.

### How often is APT Darkness Clock updated?

The app was last updated on March 6, 2018, to version 1.3. While there haven't been recent updates, the existing functionality provides core features for astrophotography timing.

### Where can I get support for APT Darkness Clock?

For suggestions and support, you can visit the dedicated section of the APT Forum at http://aptforum.com/phpbb/viewforum.php?f=26. This forum is the primary resource for user assistance and community interaction.

## Version history (last 2 releases)

### 1.3 — 2018-03-06

This app has been updated by Apple to display the Apple Watch app icon.

-Added the Moon phase visualisation for the selected night
-More detailed legend for the displayed values
-Fixed a bug in the automatic Daylight Saving Time calculation

### 1.2 — 2018-02-24

No release notes.

## Apps similar to APT Darkness Clock

| App | Rating | Price | Category |
| --- | --- | --- | --- |
| [SkySafari 7 Plus](https://appshunter.io/ios/app/skysafari-7-plus/id1567654881) | 4.7 (1,498) | $19.99 | Reference |
| [SkySafari 7 Pro](https://appshunter.io/ios/app/skysafari-7-pro/id1567658979) | 4.7 (4,914) | $29.99 | Reference |

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-06-01.*