LSTclock: sidereal time clock

LSTclock is an app for iPhone, iPad, and Apple Watch that displays the local sidereal time (LST) at registered location(s). The minimum system requirement is iOS/iPadOS 17 and/or watchOS 10.

The main features are:

Table of contents

Usage for iOS/iPadOS

Authorization for accessing location data

When the app is launched for the first time, you will see a dialog asking to access your location information. If "Allow Once" is chosen, the authorization will expire after a while and the dialog will show up again when needed.

You can choose whether you allow the app to use the precise position. If it is set to "Off", as a consequence, the LST for the location added using the "Obtain current location" button on the "New Location" sheet may become slightly inaccurate (perhaps within 10 seconds or so in most cases).

Access to your location information facilitates to add locations into the list, but is not obligatory, so you can deny it if you would not like the functionality. More details can be found in Privacy Policy section.

Main screen

The Main screen consists of three sections, followed by a set of buttons at the bottom. When auto-locking (sleeping) of the device is disabled via the "Preferences" sheet, a small indicator (crossed-out padlock icon) is displayed on the top right corner.

Local Time

The current date (YYYY-MM-DD) and time are displayed. The timezone (following the device setting) is shown on the right.

"Play/Pause" button is on the left. Once it is tapped, the clock stops updating and the text showing the local time turns into a button (the text color changes to blue), which opens the "Choose Date/Time" sheet to pick a date/time. The clock resumes updating when the "Play/Pause" button is tapped again. While the button is tapped and held, the LST at 0:00 of the day in the local time or UTC (can be chosen via the "Preferences" sheet) is shown. Please note that the "local time" refers to the device's own clock and timezone setting, not the local time of each registered location.

The Julian Date (JD) and Modified Julian Date (MJD) can also be displayed when enabled via the "Preferences" sheet.

UTC

The Coordinated Universal Time is displayed. The font size can be set to small, or the section can be completely hidden, via the "Preferences" sheet.

When the clock is paused, the UTC display turns into a button, which opens the "Choose Date/Time" sheet to pick a date/time.

LST

The LSTs are displayed as a list. The names and longitudes of the locations are shown on the left. Upon the first launch of the app, only one location, "Greenwich" at zero longitude, is registered in the location list.

Location(s) can be added via the "New Location" sheet, as described below.

Existing locations can be edited by tapping its name/longitude or by swiping to right, via the "Edit Location" sheet. Tap on the LST (when the clock is paused by tapping the "Play/Pause" button) opens the "Choose LST" sheet.

Buttons

"Edit" button
To enter the Edit mode of the LST list (deleting and reordering row(s)). Deletion of a row can also be done by swiping the row to the left, also reordering by long-tapping and dragging.
"Full Screen Mode" button (arrows icon)
To toggle the Full Screen Mode, in which only the LST at a location is displayed. Locations can be switched by swiping left/right.
"Night Mode" button (moon icon)
To toggle the Night Mode.
"Preferences" button (gear icon)
To open the "Preferences" sheet.
"Add Location" button (plus icon)
To open the "New Location" sheet to add a location to the list.

New/Edit Location sheet

The "New Location" and "Edit Location" sheets are nearly identical: the former is to add a new location to the list, while the latter is to modify the name and/or longitude of an existing location.

There exist two text fields to input the location name and longitude.

When the "Search" button below the Name text field is tapped, the app does a simple search based on the given location name and opens the "Search Results" sheet to pick one of the results.

The Longitude text field accepts an integer or real number (east-positive) in unit of degrees, e.g., "-67.755" is interpreted as 67.755 degrees (67°45′18″) West. The field also accepts "DD:MM:SS.s" format (seconds or minutes+seconds can be omitted), e.g., "138:28:21" means 138°28′21″ (138.4725 degrees) East.

When the "Obtain current location" button is tapped, the longitude of the current location is set to the Longitude text field (if you have allowed the app to access your location and the device is able to obtain the location data).

When the "Choose location from Map" button is tapped, the "Choose Location" sheet shows up.

Once the "Add" button (✓) in the "New Location" sheet is tapped, the specified location is added to the location list. By tapping the "Done" button (✓) in the "Edit Location" sheet, the name and/or longitude of the existing location are modified. If the "Cancel" button (✕) is tapped (or the sheet is swiped down), the sheet is closed and the location list is left unchanged.

Search Results sheet

This sheet is to pick a location from the results of a "Search" action in the "New/Edit Location" sheet. The search results are presented as a list and you can choose one by tapping the row. On top or left (depending on the device size and orientation) of the list, the chosen location is shown as a pin on the map. The map type can be switched between the standard one and the satellite view by using the selector at the top of the map.

When the "Done" button (✓) is tapped, the sheet is closed and the longitude of the chosen location is set into the "Longitude" field of the parent "New/Edit Location" sheet. If the "Cancel" button (✕) is tapped (or the sheet is swiped down), the sheet is closed and the "Longitude" is left unchanged.

Choose Location sheet

This sheet is to pick a location using interactive map interface. To choose a location, you need to drop a pin by tap & hold on the desired location. When you drop another pin, the previous one is automatically removed.

The map is initially centered at your location (which is marked as a blue dot) if you have allowed the app to know your location; otherwise a sort of world map shows up.

The map type can be switched between the standard one and the satellite view by using the selector at the top of the sheet.

When the "Done" button (✓) is tapped, the sheet is closed and the pin's longitude is set into the "Longitude" field of the parent "New/Edit Location" sheet. If the "Cancel" button (✕) is tapped (or the sheet is swiped down), the sheet is closed and the "Longitude" is left unchanged.

Choose Date/Time sheet

The sheet consists of three sections.

When the "Done" button (✓) is tapped, the sheet is closed and the local time, JD/MJD, UTC, and LSTs for the chosen date/time will be displayed in the Main screen. If the "Cancel" button (✕) is tapped (or the sheet is swiped down), the sheet is closed and the date/time in the Main screen is left unchanged.

Date and time

At the top of the section, there is a picker to choose the time zone. The options are "System", "UTC", -12 to +14 hours (every hour) with respect to UTC, and "Other". The default selection is "System" if the sheet was opened by tapping the local time on the Main screen, and "UTC" when Main screen's UTC was tapped. When "Other" is chosen, a text field to input the desired time zone (in "[+/-]HH:MM" format; up to +/-15 hours wrt UTC) appears.

There are a date picker and a time picker, that follow the time zone selected above. (On iOS/iPadOS 17, you may need a long press, rather than a tap, to open the date picker — seems like a bug in the OS.)

Three buttons are placed in the row below the time picker: "Now" is to reset the pickers to the current date/time; "<" and ">" are to step backward/forward by one sidereal day, approximately 23 hours 56 minutes 4 seconds. The chosen date/time is displayed above the section, while the UT, JD, and MJD are shown below the section.

LST

The list of LSTs corresponding to the chosen date/time at the registered locations is displayed. When the LST for a location is tapped, the "Choose LST" sheet shows up.

Add to Calendar

The chosen date/time can be added to the calendar as a new event. To add an event, input the name of the event and tap the "+" button on the right.

[New in version 9.3] There is a picker to choose the alarm to be set to the event. The options are none; at the time of the event; 5 minutes, 10 minutes, 15 minutes, 30 minutes, or 1 hour before the event; and "Other". When "Other" is chosen, a text field to input the desired lead time (in minutes) for the alert appears.

The event is added to your default calendar (see "Calendar" in the "Settings" app). When you use this functionality for the first time, the app asks the authorization to access your calendar. You can deny it if you would not like the functionality. The app uses the access only to add events; it does not read anything from there. More details can be found in the Privacy Policy section.

Choose LST sheet

This sheet is to pick an LST, in order to determine the date/time when the specified LST is realized at the selected location. If the preferred unit of LST is degrees ("Preferences" sheet), text fields for degrees and arcminutes show up; otherwise there are wheel pickers for hours and minutes.

Once the "Done" button (✓) is tapped and if the LST (hours/minutes or degrees/arcminutes) has been changed, the sheet is closed and the date/time (closest to the previous value) corresponding to the chosen LST is set in the parent Main screen or "Choose Date/Time" sheet. If the "Cancel" button (✕) is tapped (or the sheet is swiped down), the sheet is closed and the date/time is left unchanged.

Preferences sheet

There are six options in the Preferences sheet.

Once the "Done" button (✓) is tapped, the choices are applied and saved in the setting file on the device. If the "Cancel" button (✕) is tapped (or the sheet is swiped down), the sheet is closed without applying/saving the options.

Show JD/MJD

Toggle for the JD/MJD display. It applies to the Main screen and Widgets in some sizes.

Disable auto-lock

This option prevents the device from auto-locking (sleeping) while using the app — please be careful with battery drain.

UTC Display

Toggle for the UTC display in the Main screen: normal font, small font, or completely hidden. If "Hide" is chosen, UTC is also hidden in Widgets.

Hold on Play/Pause Button

Selection of the time to be used when the "Play/Pause" button on the Main screen is tapped and held. The LSTs at 0:00 of the day in the local time or UTC are shown.

LST Unit

Selection of the preferred unit of LST, hours (0 to 24) or degrees (0 to 360).

Longitude Format

Selection of the preferred format of longitude, sexagesimal (like DD:MM:SS.s) or decimal degrees (like DD.ddd). This option is applied to the list of LSTs in the Main screen and the Longitude field in the Edit Location sheet (the latter still accepts both formats regardless of the setting).

Widgets

 

Widgets can be placed on the Home Screen and/or Lock Screen. A widget displays the current LST at a selected location (also UTC and/or JD/MJD in some sizes, if configured so in the "Preferences" sheet), refreshing every minute. Multiple widgets can be placed concurrently.

StandBy widgets are also supported. The contents are the same as the Home Screen widgets.

The widgets are configurable (i.e., you can choose the location from the list). If the chosen location no longer exists, the first location in the list is shown instead.

If you find widgets are not working correctly, please try the followings:

(Caveat: when you perform time-critical observations or something like that, it is recommended to open the app to check the LST, rather than to rely on the widgets — updating of the widgets might not be 100% reliable.)

Other features

Night Mode

In order to help dark adaptation, the UI elements and background colors are set to red and black, respectively, regardless of the system appearance setting. (Caveat: due to technical reasons, some UI elements remain bright.) This can be turned on/off by using the button on the Main screen.

Import locations from "Maps" app

Locations can be imported from the "Maps" app using the "Share" () functionality of the OS. Although the feature works only for Apple's "Maps" app, the LSTclock app may also show up on the Share sheets in other apps, such as Google Maps (apologies for the inconvenience).

It may take up to half a minute for LSTclock app to recognize the newly added location(s).

Multitasking (iPadOS)

The app supports multitasking features on iPadOS. Multiple windows can be opened concurrently.

Usage for watchOS

Authorization for accessing location data

When necessary, a dialog asking the authorization to access your location information pops up. If "Allow Once" is chosen, the authorization will expire after a while and the dialog will show up again when needed. This setting follows that on the paired iPhone, so you may not see the popup if you have already chosen "Allow While Using App" on the iPhone.

The app uses your location (if allowed) when you are going to set the current location in the "New Location" sheet. See also the Privacy Policy section.

Main screen

[Changed in version 9.3] There are three buttons at the corners of the screen. The "Night Mode" button (top left; moon icon) is to toggle the Night Mode. The "Preferences" button (top right; gear icon) is to open the "Preferences" sheet. The "Add Location" button (bottom right; plus icon) is to open the "New Location" sheet.

The current UTC is displayed at the top of the screen. [Changed in version 9.3] This can be changed to JD or MJD, or completely hidden, via the "Preferences" sheet.

The LSTs at the locations in the location list are displayed. The list can be scrolled by rotating the Digital Crown (or swiping up/down), and reordered by long-tapping and dragging items. By swiping a list item to the left, the item can be deleted. By swiping a list item to the right, the item can be edited via the "Edit Location" sheet.

New/Edit Location sheet

The sheet is to add a new location into the list, or to edit an existing location.

A text field to input the name of the location is at the top of the sheet.

Three wheel-pickers for degrees, minutes, and east/west of the longitude are in the middle of the sheet. The pickers are scrollable by rotating the Digital Crown, or swiping up/down. (The longitude is rounded to the nearest arcminute. The maximum error due to rounding is 0.5 arcminute, i.e., 2 seconds in LST.)

The button at the bottom left is to obtain the current location. The current longitude is set to the pickers described above, if you have allowed the app to access your location and the device is able to obtain the location data.

Once the "Add/Done" button (✓) is tapped, the changes are saved. If the "Cancel" button (✕) is tapped, the sheet is closed and the location list is left unchanged.

Preferences sheet

There are a toggle switch and two pickers in the Preferences sheet.

Once the "Done" button (✓) is tapped, the choices are applied and saved in the setting file on the device. If the "Cancel" button (✕) is tapped, the sheet is closed without applying/saving the options.

LST Unit

Toggle for the preferred unit of LST, hours (0 to 24) or degrees (0 to 360).

Main screen item

Picker to choose an item to display in the Main screen. [Changed in version 9.3] The options are UTC, JD, MJD, and None.

Widget item

[New in version 9.3] Picker to choose items to display in the complications ("Rectangular" style) and widgets. The options are "UTC and JD" and "UTC and MJD".

Complications/widgets

 

The app complications can be placed on the watch faces. The complications are configurable (i.e., you can choose the location from the list). If the chosen location no longer exists, the first location in the list is shown instead.

A complication can display the current LST at a selected location. In the "Rectangular" style, the current UTC and JD/MJD (following the setting in the "Preferences" sheet) are also displayed. The complications are scheduled to be updated once a minute.

Smart Stack widgets are also supported. The contents are the same as the "Rectangular" complications.

(Caveat: updating the complications may not be 100% reliable, and therefore, when you perform time-critical observations or something like that, it is recommended to open the app to check the LST, rather than to rely on the complications.)

Other Features

Night Mode

In order to help dark adaptation, the UI elements and background colors are set to red and black, respectively. (Caveat: due to technical reasons, some UI elements remain bright.) This can be turned on/off by the "Night Mode" button on the Main screen.

Sync from/to iPhone

If the app is installed on iPhone and paired Apple Watch(es), the location list should automatically sync between the devices. The sync is not done on an item-by-item basis, but the entire list is transferred from one device to the other. Upon syncing, the device on which the list was lastly modified behaves as the primary, where "modified" includes addition, removal, modification, and/or reordering of the items. (If the sync does not happen for some reason, please try quitting/re-launching the app or modifying the list on one of the devices to trigger syncing.)

It is optional to have the app installed on iPhone; the app on Apple Watch can work stand-alone.

Double-tap gesture

The double-tap gesture on Apple Watch Series 9+ and Apple Watch Ultra 2+ is supported (requiring watchOS 11). The gesture is assigned to scrolling the LST list on the Main screen; the "Add/Done" button on the "New/Edit Location" sheet; and the "Done" button on the "Preferences" sheet.

Version history

See also

For Mac users (running Mac OS X 10.4 Tiger – macOS 10.14 Mojave), a Dashboard widget providing a similar functionality is available.

Disclaimer

The app and this website are provided "as is". The developer does not make any warranties and is not responsible to any harm or inconvenience the app/website might cause.

Privacy policy

The app uses your location in the following occasions:

And the app uses your calendar to add new events via the "Choose Date/Time" sheet on iOS/iPadOS. The app does not read anything from your calendar. On iOS/iPadOS 17+, "Full Access" permission is no longer required but "Add Events Only" is sufficient.

At any time you can deny or disable the app's access to your location and/or calendar using the "Settings" app; the app can work without these functionalities.

When a location is added to the list, it (longitude only) is saved into the app's setting file on the device. Besides that, the app does not store, share, or send your location, calendar contents, or any other kind of private information.

When the developer receives messages from users via email (the address is in the footer of this page), the information contained in the messages is used only to provide support and not shared with others.