# LSTclock: sidereal time clock — Local sidereal time clock > Displays local sidereal time and Julian Date for registered locations. (iPhone/iPad app by Tsuyoshi Sawada.) - Source: https://appshunter.io/ios/app/lstclock-sidereal-time-clock/id1510148631 (this page in markdown: same URL + `.md`) - Developer: [Tsuyoshi Sawada](https://appshunter.io/developer/1510148630) - Category: Utilities, Education - Price: Free - Rating: 3.80/5 from 10 App Store ratings · 11 written reviews indexed - Age rating: 4+ - Requires: iOS 17.0 · 15 MB - Languages: English - Released: 2020-04-26 - Data updated: 2026-07-27 - Monetization: free - User reviews in markdown: https://appshunter.io/ios/app/lstclock-sidereal-time-clock/id1510148631/reviews.md ## What is LSTclock? LSTclock is an iOS/iPadOS/watchOS app that displays the local sidereal time (LST) at registered location(s). On iOS/iPadOS, it can also calculate LST and Julian Date for any date and time. The list of locations can be synced between iPhone and paired Apple Watch(es). ## Key features - Local sidereal time display - Julian Date calculation - Supports multiple registered locations - Location sync between iPhone and Apple Watch - Date and time specific calculations ## Recent user reviews (10 of 11) All indexed reviews: https://appshunter.io/ios/app/lstclock-sidereal-time-clock/id1510148631/reviews.md ### 5/5 — Amazing app *2026-01-27, version 8.4* Thank u for making this app, could I suggest a feature to add LST based on custom local time? I.e if local time was 3 hours in advance or less to predict future / backtrack LST? Update: the dev just replied to me and explained the hidden Hmm feature I was not aware of: taping the play/pause button let you edit specific time! Killer feature indeed, which let me preview upcoming LST in local time! This app is wonderful to have: works on all devices (works on Mac as well as widgets which is all I need) Clean, modern and easy to use It’s free! I’m so grateful ### 5/5 — Exceptional and multifunctional *2025-12-25* There is much to discover about sidereal time with this app. Take the time to read the user guide to access multiple functions. One suggestion for the developer: a user setting to allow the app to override the lock screen timeout optionally for a constant on display setting. Thank you for bringing this very useful app to the iOS environment. **Developer response:** Thank you for the comment. In version 9.1, an option to prevent the device from auto-locking (sleeping) was added. I hope it helps. ### 5/5 — Almost; but, not quite. *2024-12-15* Astronomers often need to use standard and local sidereal time which is done in the app; but more importantly for record keeping, they also need Julian and Modified Julian Dates. The app does not show JD or MJD and really needs to do this to be useful and bumped from three to five stars. Having to go to settings for time (which is not self explanatory) in order to get the JD and MJD is a pain. Just display both under the LST. Hope the developer takes this under advisement. 14 December 2024 UPDATE: Tsuyoshi Sawada quickly responded with a note through the Apple App store that he added an optional setting to switch on or off the JD/MJD in his LSTClock and I tested it this evening when making my observations. It is a perfect solution to a long term issue that I have struggled with in my work having to look things up and compute JD and MJD with online calculators. Tsuyoshi, your solution is perfect! Thank you for responding so quickly and as promised, your app is not rated ⭐️⭐️⭐️⭐️⭐️ and more. Thank you so very much! **Developer response:** Thank you for the suggestion, I added an option to show JD/MJD in version 8.3. ### 3/5 — Almost; but, not quite. *2024-12-03* Astronomers often need to use standard and local sidereal time which is done in the app; but more importantly for record keeping, they also need Julian and Modified Julian Dates. The app does not show JD or MJD and really needs to do this to be useful and bumped from three to five stars. Having to go to settings for time (which is not self explanatory) in order to get the JD and MJD is a pain. Just display both under the LST. Hope the developer takes this under advisement. **Developer response:** Thank you for the suggestion, I added an option to show JD/MJD in version 8.3. ### 1/5 — Widget broken *2024-11-21* Widget in iOS 18 still broken. ### 3/5 — Extreme minimalism *2023-05-12* The app works but I can’t seem to get the Lock Screen widget to show the LST. It shows a time when selecting the widget as a preview, but not on the active Lock Screen widget itself. I’ve tried all the privacy/notification settings I could find, updated iOS and reinstalled. The app doesn’t show up in some lists where other app settings would appear. ### 2/5 — “Local” sidereal time *2023-04-19* In relationship to my actual location, it’s not showing me accurate side real time. It’s showing me side real time for Switzerland, but I’m not in Switzerland. I have my location on, but it’s not telling me what my local sidereal time is ### 5/5 — Small bugs but unique in function *2022-12-11* There seems to be a bug in how the Watch app enumerates complications, and took a few restarts and resets before I could get everything just right, but this app is unique in that you can get sidereal time with just your longitude and display it on the watch face. ### 2/5 — No Night Mode *2021-07-16* No Night mode, I.e dim red light **Developer response:** Thank you for the feedback. Night mode is added in version 3.5 (I hope it helps). ### 5/5 — Light and easy *2021-07-09, version 3.4* This app works well and best of all, it has a small footprint. It’s interface is uncluttered and displays LST clearly on the phone and watch. It doesn’t have a location lookup for cities etc but does have a current location button which suits me. ## Frequently asked questions about LSTclock ### What is LSTclock? LSTclock is a free utility app for iOS, iPadOS, and watchOS that displays local sidereal time (LST) for your registered locations. It can also calculate the Julian Date for any given date and time. ### What devices does LSTclock support? LSTclock is available on iPhone, iPad, and Apple Watch. You can sync your registered locations between your iPhone and paired Apple Watch devices. ### How accurate is LSTclock? LSTclock provides calculations for sidereal time and Julian Date. While the app itself is free, user reviews indicate an average rating of 3.8 stars from 10 ratings, suggesting a generally positive but not perfect user experience. ### Does LSTclock have ads? No, LSTclock does not contain advertisements. It is a free application without any in-app purchases or ads. ### When was LSTclock last updated? The latest version of LSTclock, 9.3, was last updated on March 20, 2026. The app was initially released on April 26, 2020. ### What is the age rating for LSTclock? LSTclock has an age rating of 4+, making it suitable for a wide range of users. This rating is based on its content and is generally considered safe for children. ### Can LSTclock calculate past or future sidereal times? Yes, on iOS and iPadOS, LSTclock can calculate the local sidereal time and Julian Date for any specific date and time you input. ## Version history (last 5 releases) ### 9.4 — 2026-07-07 - UI tweaks. ### 9.3 — 2026-03-20 - Added a functionality to set an alarm for calendar events created from the "Choose Date/Time" sheet (iOS/iPadOS). - Modified the layout of the Main screen (watchOS). - Added an option to hide UTC/JD/MJD on the Main screen (watchOS). - UI tweaks. ### 9.2 — 2026-02-21 - Worked around the issue with "Share" from Maps app on iOS/iPadOS 26. - Added a functionality to set date/time in desired time zone on the "Choose Date/Time" sheet (iOS/iPadOS). As a side effect, settings for UTC display (show/hide and font size) are reset to the default values upon the update of the app (sorry for the inconvenience). - Assigned swipe-to-right gesture to edit existing locations (iOS/iPadOS). - UI tweaks. ### 9.1 — 2026-02-07 - Improved darkness of the Night Mode. - Added an option to disable auto-locking (sleeping) while using the app (iOS/iPadOS). - Added a map type toggle on the "Search Results" sheet (iOS/iPadOS). - Added a functionality to edit existing locations by swiping to right (watchOS). - Bug fixes and UI tweaks. ### 9.0 — 2026-01-28 - Dropped support for iOS/iPadOS 16 and watchOS 9 (sorry for the inconvenience). - Adapted to modern OS look & feel, including Liquid Glass and new icon. - Known issue on iOS/iPadOS 26: "Share" sheet from the Maps app does not work because of internal changes of the OS. In this version, the error message was improved to clarify the situation. - Bug fixes and UI tweaks. ## Apps similar to LSTclock | App | Rating | Price | Category | | --- | --- | --- | --- | | [Touch-N-Stars](https://appshunter.io/ios/app/touch-n-stars/id6744902856) | 5.0 (6) | Free | Utilities | | [Local Sidereal Time](https://appshunter.io/ios/app/local-sidereal-time/id1256725300) | 4.7 (1,055) | Free | Utilities | | [Custom Word Clock - TextTime](https://appshunter.io/ios/app/custom-word-clock-texttime/id6449908609) | 5.0 (4) | Free | Utilities | | [Desktop Astro Clock](https://appshunter.io/ios/app/desktop-astro-clock/id1588806370) | 3.7 (3) | Free | Utilities | | [@Beat: Internet time](https://appshunter.io/ios/app/beat-internet-time/id1570173118) | 4.4 (17) | Free | Utilities | | [Polar Scope Align Pro Watch](https://appshunter.io/ios/app/polar-scope-align-pro-watch/id986082042) | 4.9 (50) | $4.99 | Utilities | ## Related topics [sidereal time](https://appshunter.io/ios/topics/sidereal-time) · [local sidereal time](https://appshunter.io/ios/topics/local-sidereal-time) --- *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 2026-07-27.*