What the Turkey, Earth and ISS Screens Show in Uzay Gunlugu

By Nesim Razon, independent Android developer

Uzay Gunlugu (Space Journal) mixes a daily space card with satellite images and live numbers. This guide explains what each screen shows, where the picture or number comes from, how fresh it is and where its limits are. The app's interface is in Turkish, so the Turkish labels are given in brackets where they help.

The big picture: one daily file and a few live sources

The app has five tabs: Today (Bugün), Turkey (Türkiye), Earth (Dünya), ISS and Album. They do not all work the same way. The 61 space cards are bundled inside the app, so they open even without internet. Everything else is fetched online.

Most of the changing information comes from one small data file that the developer publishes once a day. It holds the Earth frames, the asteroid list and a link to the astronomy picture of the day. The app downloads it when you open it and keeps a copy. If the download fails, it shows the last saved copy, so numbers can be older than they look when you are offline. The satellite image of Turkey and the world map come straight from NASA's public GIBS/Worldview service. The ISS position comes from a separate public service, wheretheiss.at.

One important note: Uzay Gunlugu is an independent app. It is not affiliated with or endorsed by NASA. It only uses publicly available images and data, and it names the source on every screen.

The card of the day and the album

The Today screen opens with the card of the day: a space photograph, its category (for example a nebula, a planet or Earth from orbit), a short note in Turkish, the image credit and an Open in archive link to the original page. The notes were written by hand for the set of 61 cards. They are meant as a quick, friendly caption, not a full lesson.

The card is not random on your phone. The 61 cards are put in one fixed shuffled order, and the number of days since a fixed date decides which one is today's. So everyone sees the same card on the same day, and after 61 days the cycle starts again. Tap the picture to open it full screen, zoom in, share it or set it as wallpaper.

Streak and album: how the counting works

• The first time you open the app on a given day, that day's card is added to your album automatically. A box on the Today screen tells you when a new card was added. Opening the app again the same day changes nothing.
• The streak counts consecutive days. If you opened the app yesterday and open it today, it grows by one. Skip a full day and it starts again from one. The flame number next to the title shows the current streak, and it disappears when the streak is broken.
• The album shows how many of the 61 cards you have collected, with collected ones first. The album and streak are stored on your device, not in an account.

Turkey from space

This screen shows a true-colour satellite picture of Turkey and the sea around it. It comes from the VIIRS instrument on the NOAA-21 satellite, served through NASA's GIBS/Worldview. True colour means it looks roughly like a photograph: land, sea and clouds.

The default image is yesterday's, built from the satellite passes of that day. There is no image for today because it has not been assembled yet. Use the previous day and next buttons to move through earlier days; the date is shown between them. Clouds are the main limit: on a cloudy day you simply see clouds, and parts of the land can be hidden.

Night lights: a fixed map, not a live view

The Night lights button shows how cities glow after dark. It is easy to misread, so note this: it is a fixed map built from satellite images collected over the whole year 2016, and the app labels it as a yearly average. It is not last night's view and it has no date buttons.

Use it to compare regions: big cities, coastlines and highways stand out as bright areas, and sparsely populated regions look dark. Do not use it to judge today's situation anywhere.

Earth now: the rotating Earth

The Earth screen plays a short loop of pictures of the whole planet taken from a camera on the DSCOVR spacecraft (the EPIC instrument), about a million kilometres away. The app takes the frames of the newest day available and plays them one after another, so you can watch the planet turn. Play and Pause control the loop.

Under the image you see the time of the current frame in UTC (not your local time), the date of the frames and the latitude and longitude at the centre of the picture. The frames are not live: the newest set is usually from a day or two earlier, and the date tells you exactly which. The sunlit side of Earth is the part you see, which is why the picture changes through the day. If frames cannot be loaded, the screen asks you to check your connection.

ISS now: reading the numbers

The ISS screen puts a marker on a world map. The position is requested again every five seconds while the screen is open, so you can watch the marker creep along. The map behind it is a still picture of Earth's surface, not a live view with clouds or day and night shading.

Below the map the app lists four rows. Latitude and longitude give the point on the ground directly under the station. Height is the altitude above the surface in kilometres; the station orbits at roughly 400 km. Speed is shown in kilometres per hour. The last row says whether it is day or night on the ground below the station. A button opens a live camera view from the station on YouTube in your browser, if that stream is available at the time.

Remember what this is not: the marker is a position on a map, not a prediction of when the station will pass over your house, and the app does not tell you when to look up.

Asteroids this week: a list to read, not an alarm

The Today screen ends with a short list of near-Earth asteroids. It comes from NASA/JPL's CNEOS and covers close approaches in roughly the coming two weeks, up to a fixed distance limit. The app shows the first five by date. Each row gives the date and time (UTC), the asteroid's designation, how far away it passes, an estimated size and its speed in kilometres per second.

Distance is written in Moon distances, because kilometres are hard to feel. The Moon is about 384,000 km away, so a pass at 8.0 times the Moon's distance is roughly three million kilometres. If an asteroid passes closer than the Moon, the row says so as a percentage of the Moon's distance. Size is only an estimate worked out from the object's brightness, and the app compares it with a car, a bus, an apartment building or a football field to give you a feel for it.

These are routine, scheduled flybys. The list is informational and is not a hazard warning.

Quick limits checklist

• Interface and card notes are in Turkish only for now.
• Satellite picture of Turkey: yesterday at the newest, and cloud cover can hide the ground.
• Night lights: a fixed 2016 yearly composite, never daily.
• Rotating Earth: recent frames, usually not from today; the time shown is UTC.
• ISS: position refreshes every five seconds, but the map under it is a still image.
• Asteroids: estimated sizes and a short window; not a safety tool.