Xasteria for iOS


Notice: Xasteria now has its own mirror of the 7Timer service, for more reliability and quicker response times!

Xasteria brings the Astronomical-oriented ASTRO world weather forecast of the service 7Timer! to any iOS 6.0 or later device. You can use your device GPS for a forecast of your location, enter manual coordinates or search of a location online.

7Timer! is mainly derived from the NOAA/NCEP-based numeric weather model, the Global Forecast System (GFS) and gives you a forecast for the entire globe with a resolution of about 20km at 3-hour intervals.

Xasteria is available iPhone/iPod/iPad with iOS 6.0 or higher.

Download on the App Store


Graphic/Visualization Modes

Xasteria provides you with a choice of 3 visualization modes for the data: the new 7Timer! ASTRO graphics, which tries to be quick to read by using different visuals per category and not overwhelming with data that is not useful (e.g. if humidity is low, you don’t need to know the exact percentage), the color-stripe graphics similar to some other astro-forecast services and a raw text mode.

7Timer! Mode

Stripe Mode

Text Mode


Available Data

A list of available data categories, along with the graphics that are used by the 7Timer! graphic mode and the stripe graphic mode.

  • Moon phase.
  • Cloud cover. Will give you the cloud cover forecast from 0% to 100% (worst).


  • Astronomical seeing. Turbulence and temperature differences in the atmosphere can reduce the amount of detail visible through a telescope, especially with high magnification on planets.


  • Atmospheric transparency. Water vapor can reduce the transparency of the atmosphere. Good transparency is required for low contrast targets like galaxies and nebulae.


  • Temperature. Apart from your comfort level, a low temperature can affect the cool-down time of your equipment.

  • Humidity. High humidity can, depending temperature, telescope type etc, lead to quicker dew formation on optics.


  • Rain/Snow.rain
  • Atmospheric instability. Indicates when there is a high chance of a thunderstorm (based on a calculation of the lifted index).


  • Wind. The app will either warn you about high wind (in graphic modes), or show the wind strength in the beaufort scale (text mode). Strong winds apart from comfort affect the stability of your telescope and can be crucial for astrophotography.


Language Support

Xasteria is available in English, Greek and French (translation by Damien Kusior). If you’d like to translate it to your language, contact me about it!

Pronunciation & Meaning of The Name “Xasteria”

Xasteria is a Greek word (Ξαστεριά) which means a night without clouds with all the stars visible (“full of stars” is the closest literal translation). The Greek pronunciation is “Ksa-steh-RYA” (rhymes with kumbaya), however I don’t really expect English speakers to go for that, so I’d be fine with something like “Za-STEE-ree-ah” or perhaps a “hybrid” pronunciation of “Ksa-STEE-ree-ah”.

Polar Scope Align Pro

There is a special version of Xasteria in the Polar Scope Align Pro app, which adds the ability to switch to night-mode (and access to that app’s quick-dim function) and also can take advantage of the app’s location manager.


  • How do I switch to XXX language?

Xasteria currently has support for English, French and Greek and iOS will automatically load the language that is set on your phone. If you want to set your phone to a language Xasteria does not support (e.g. Spanish, Chinese etc), but also “choose” specifically one of the Xasteria languages, then first switch your device language to the Xasteria language you prefer, which will make Xasteria load into that, and then switch it back to the unsupported language.

  • How often is the forecast recalculated?

The 7Timer! forecast uses NOAA data. NOAA updates their data every 6 hours, hence 7timer itself recalculates the forecast at the same frequency.

  • What is the altitude correction?

This is something you should normally leave “off”. However, if you are on the top of a steep mountain, it is likely that the resolution of the forecast system (about 20km) is not enough to give you readings specifically for the peak you are on. This will become obvious if you notice the Xasteria temperature reading being much higher than the actual temperature at your location. In that case you can try the +2 km correction (or the +7 km in a couple of places in the world).


If you have any questions or problems with your app, the quickest solution is to use the Contact page to write directly to the developer. Or you can post your suggestions, questions in the comments below

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5 thoughts on “Xasteria for iOS

  1. Ari Siqueira says:

    I downloaded Xasteria for iOS but could not yet figure out how to use it for a polar alignment. Have you published detailed instructions or perhaps a tutorial?
    Thank you.

    • ecuador says:

      Hi. I am not sure I understand what you are trying to do. The Polar Scope Align app is for polar alignment. There are general instructions (button on top left on the main screen) and also specific instructions for your polar scope (Reticle Help button in Settings screen after you select your Polar Scope Reticle).
      Xasteria is a different app that gives you a weather forecast.
      The connection between the two apps is that the Pro version of Polar Scope Align includes a night-vision enabled version of Xasteria.
      Hope this clears it up.

  2. Curtis says:

    7Timer is down, can you use Meteobule’s astronomical data for Xasteria?

    • ecuador says:

      Hello Curtis. Thanks for the suggestion. I looked at Meteoblue, however access to their data is relatively expensive (especially for a free app like Xasteria). I could make their website open for your location inside the app to cross-check the 7Timer data (when it works again – shouldn’t be long now), or have as an extra source if the 7Timer data is not available. I’ll add that to the next version. I haven’t found a proper global data feed to use when 7Timer is not working I am afraid, and the main reason I made the app is specifically for that data, as there were iOS apps like Clear Outside (and Meteoblue has their own) providing other sources, but it is always good (especially in the UK where weather forecasts don’t often agree), to have an extra source. Plus, I find the 7Timer data among the most readable – I hope it doesn’t take too long to return now (a bit bureaucracy is delaying the process).

      • ecuador says:

        A delayed note to say that for a while now I have been hosting the main 7Timer! mirror, so we haven’t had any downtime for the service since. The app still gives you quick links to Meteoblue and Clear Outside.

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