The night sky is getting busy. On a clear night, you can see a satellite or two passing among the stars. How do you know if that is a spent rocket booster, the Hubble Space Telescope, or a crewed space station? What was the brief flash of light? Was it a meteorite or a satellite?
The first artificial satellite, the Soviet Union's Sputnik 1, was launched in 1957. Many of these were satellites for scientific, telecommunication, and military uses, while the rest were spent rocket boosters and space debris. The International Space Station is the largest object. The 490-ton crewed space laboratory is about the size of a football field and includes an acre of solar panels. At the other end of the scale, there are tiny CubeSats that measure only 10 centimeters on each side.
How to see and track the International Space Station.
Several commercial operators have begun launching thousands of communications satellites designed to deliver broadband internet access across the globe. While most of those aren't particularly bright, the SpaceX Starlink satellites create a buzz among skywatchers immediately after they are launched. They appear as long chains of dots as they move across the night sky.
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Since everyone carries a phone with them, mobile apps are ideal tools for tracking the satellites. They can tell you which object you are seeing, alert you just before a space station appears in the sky, and show you exactly where to look for it.
When sharing the fun of satellite-watching with friends and family, the most useful satellite apps use your device's compass and gyro to guide you where to look in the sky. The best mobile apps for spotting artificial denizens of the night sky. Satellite basics first!
Even when the sun is below the horizon, satellites are visible to us because they are high enough overhead to be illuminated by sunlight. Most satellites are seen an hour or two before dawn and after dusk. When a satellite passes by, it enters the shadow of the Earth, a patch of the sky where the sunlight can't reach it. Satellites can be seen when they leave the shadow.
A satellite's brightness depends on its distance from you and how much sunlight it gets from you. Most satellites shine with a steady light, but objects that are tumbling can glow and dark as they travel. Satellites don't have lights, and no artificial light would be bright enough to spot from the ground. An aircraft is an object with flashing lights.
Satellites are kept in view from the same spot on Earth at all times. They need to go above the equator at a distance of over 30,000 km above sea level. The type of satellite will be dim. You might see one moving very slowly against the background stars while using your telescope. In the night sky, there is a strip of satellites below the equator. The Earth's shadow covers a small patch of the sky so they can appear all night long. You aim your satellite TV dish at these satellites. Many of the apps in the app store are not designed for skywatching.
Spacecraft that need to move around the Earth at a modest rate closer in to the Earth's surface, around 12,600 miles (20,200 km) above sea level. The navigation networks of Russia, Europe, China, India, and Japan are included. The satellites are invisible to the naked eye, but they can be seen through your telescope.
Satellites that need to closely observe Earth's surface and weather, or that are too heavy to lift into high orbits, are placed in low Earth orbit. These are the bright satellites that are in the sky. The Earth's elliptical shape falls into a range. To allow for high-resolution close-up views of our planet, the lower limit is 190 miles. The upper limit is 1,250 miles, just inside the protective shell of Earth's Van Allen radiation belts.
Satellites need to travel between 90 and 225 minutes to complete a single trip around Earth. The International Space Station, the Hubble Space Telescope, China's Tiangong Space Station, the National Oceanic Atmospheric Administration weather satellites, and Europe's Envisat are some of the well-known examples. The American Atlas-Centaur and Russian COSMOS rocket upper stages also fall into this class.
Individual modules were launched and connected to the space station. The first component, dubbed Zarya, was launched on a Russian rocket in 1998. Nauka was added to the name of the Multipurpose Laboratory Module-Upgrade on July 29, 2021. The solar panel array on the space station rotates constantly to keep them focused on the sun, and the reflections from them give us a steady glow as it flies overhead. The most easily observable object is the ISS. The moon and Venus shine in the night sky.
The International Space Station is one of the objects that completes one of the Earth's moons every 92.50 minutes or 16 per day. The Earth has a rotation to the east by 22.5 degrees when the International Space Station completes one mission. A series of diagonal strips are covered with each strip west of the previous one, if the station is tilted with respect to the Earth's equator. Almost all of Earth will be flown over every few days.
TheISS is only able to travel between the Kamchatka Peninsula and the Falkland Islands because it is inclined 51.6 degrees from the equator. It takes 63 days for the space station to reappear over your house at the same time of night because it passes over the same spot on Earth every three days. The station doesn't need to be straight overhead to see it. If the conditions are right, you should be able to see one or two passes east and west of your location.
The sun's position, location, and orbital details can be used to predict where you will see it. Higher passes can be up to 5 minutes from horizon to horizon, often passing nearly overhead. The station's maximum elevation above the horizon will be so low that it will be hard to see if you are east or west of your location. The app will show the maximum height above the horizon in degrees, direction of motion and duration. An icon is offered to distinguish a high-quality pass from a mediocre one. You can use the better apps to limit the poor spotting.
The Chinese space station was launched. Over the next several years, components will be added. The core module with a mass of 22.6 metric tons and dimensions of 54 by 14 feet is in the middle of the sky at an altitude of 241 miles. It swings between 41.58 degrees north and south every 92 minutes. It's only observable from latitudes within 45 degrees of the equator.
We will look at two of the best apps for skywatchers.
The most powerful and comprehensive satellite tracking app I have found is the Orbitrack app for Apple products. Southern Stars is the developer of the SkySafari app. Users of that app will already be familiar with its user interface because the main toolbar looks the same.
The app tracks every object that is large enough to be seen. All data is stored in the local area and can be used without a data connection. Dragon crewed and cargo deliveries to the International Space Station are just two of the new objects that Orbitrack adds as they are launched. Everything is included for an inexpensive purchase price.
Special interest satellites, those that will be visible tonight, are the first items on the search menu. The sections for Weather, Earth Resources, Communication, navigation, Scientific, and Miscellaneous satellites are divided into sub- categories with the entries listed in order alphabetical. Satellites are highlighted with brighter text. If you enter all or a portion of the name into the search bar, you can find an individual satellite.
The satellite's physical characteristics, position in the sky, location on Earth, and its orbital parameters are included in the object info tab on the page. You can find upcoming passes by scrolling down. The clock icon can be used to show the sky at a certain time or to alert you for the pass. An object description tab opens a page with information about the satellite.
The lock screen of your device has notifications on it. You can change the amount of advanced warning time in the main menu. Unless you are a ham radio operator, I recommend enabling Sort Lists by Pass Time and showing Visible Passes Only.
Sky View, Satellite View, and Ground View are some of the modes that Orbitrack displays satellites in.
Sky View shows the sky at your location, or from any other location in the app. Satellites have green symbols. I prefer the option to also draw the selected satellite's orbit. The magnitude limit value can be adjusted to control the number of satellites shown. The default value is too dim to see with the naked eye, but is close to binoculars. You can choose between a flat horizon and a photorealistic one, and decide which stars and planets you want to see. In Sky View mode, Orbitrack is a very good basic sky charting app.
The SkySafari app series uses the same time controls. They allow for a lot of new things. You can see the passes that will happen that night if you are planning an observing session. If someone tells you that they saw a satellite pass, you can enter the date, time, and location into the app and see which satellites were in the sky. It is possible to allow for a bit of uncertainty in the time it took for it to happen. If you want to take a picture of the satellite, you can make time flow faster.
Sky View can be used to identify passing satellites. With the app's time set to Now, hold your device up to the sky in portrait mode to invoke the augmented reality feature. If you have a compass and gyro sensor on your device, the app will show the part of the sky you are pointing at. You can use the info button to learn more about the satellite. Another trick is to tilt the device downwards to show the sky below the horizon. The arrow on the locate button will lead you to the target.
The Virtual Reality feature on the iPhone allows users to explore a virtual representation of the night sky by moving their heads around. Simple voice commands will change the amount of zoom in the display while in virtual reality mode. If you prefer, voice control can be disabled in the settings menu.
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A zoomable 3D rendered model of the Earth surrounded by green dots is displayed. To see the satellite's name and location, tap a dot. The display will be very cluttered. You can choose which classes of satellites to include in the settings menu. It's fun to see how the distant satellites compare with the low Earth satellites such as the Hubble Space Telescope. You can show only the selected satellite if you want to display all satellite names.
You can see a 3D rendering of major satellites in Satellite View. By using your finger you can see the satellite from any angle and watch it as it moves through the sky. Launching virtual reality mode allows you to fly around the satellite by moving your device.
The fourth mode is called Ground View. It shows a top-down view of the selected satellite. The indicator is displayed along with the orbital track. The selected satellite front and center will be brought by tapping the Centre icon.
RunaR's free app is a favorite. The free version of the app tracks the space station. An extension pack will track more satellites, planets, and even comets.
The user interface of the app is easy to understand. The main page has upcoming events ordered soonest to latest and distinguishes them by color codes. An icon is sized to represent the quality of the pass. The local time of the start and end of the satellite pass, as well as the angle above the horizon at which it will occur, completes the information provided. The app can show the weather as a symbol and link to your local weather forecast. At a glance, the sunrise and sunset times are available.
If you only want to observe certain types of events, you can use the filters on the Events page. You can set limits on the minimum elevation, minimum brightness, all-day or night-only passes, and even set the quality threshold within each object category. You can refresh the data manually. There is a time until the next event.
There are three tabs labeled Radar, Details, and Live Video on the phone version of ISS Detector. It is revealed by tapping a panel. Swiping between switches. The current location above Earth and in the sky is shown in the Details pane. There is a map of Earth that shows the current location. A double-tap enlarges the map for pan, pinch and zoom.
The Radar pane makes the ISS Detector shine. You can align your device with the satellite in real-time with the display of a dynamic compass and tilt indicator. The point of maximum height is shown in a blue arcs. You can rehearse a pass to see how it will cross the sky. You can track the satellite with the help of the compass needle during a live event. The moon and planets are displayed to help orient you. To display pass and timings planet labels, hold a finger on the pane. You can choose between compass mode and a whole sky star map, where the object's track and direction through the stars are clearly indicated. If you have purchased the upgrade, the app will guide you to any visible comets.
You can watch the video from the International Space Station in either HD orSD mode, but an internet connection is required. The pass list, Radar, and Detail panes are shown at the same time on a larger display, but the live feed option is not available.
The silent periods and notification of impending passes are offered by the ISS Detector app. You can add passes to your calendar. I haven't tried out the feature that allows the app to link to a rotator to allow a ham antenna or telescope to track a satellite. It sounds like a lot of fun.
Satellite predicting tools are available to users of popular sky charting apps. Satellites is a plug-in that allows searches for names in the sky, but it does not give predictions.
The free and paid versions of the Stellarium Mobile app for Android and the paid version of the Stellarium Plus for iPad offer lots of information about satellites, and terrific tools for predicting them and seeing them. Only one or two satellites can be seen on the sky using the default settings. To see everything passing overhead, long-press the labels menu and run the satellites sliders to the right. If you want to expand the information panel, tap on a satellite to select it. You can review data about the object and read its entry on the internet. You can fly around the object with finger gestures if you tap the label.
To summon a graph of that satellite's elevation, tap the button labeledVisibility. Higher altitudes suggest brighter passes. The sky can be changed by moving a slider at the bottom of the graph. The same thing happens when you tap a pass. If you tilt the phone up to the sky, it will show you the annotated sky in front of the real thing. The real object will be in front of you if you center the satellite in the display. You can find your phone by hitting the locate button in the toolbar.
The SkySafari app can be used to search for individual satellites or to select from a list of Current Satellites that can be sorted by brightness, height, rise time, and more. By default, satellites aren't displayed in the sky, but the current ones can be plotted as small blue circles on the sky.
A symbol on the sky or a satellite in a list can be used to call up information. There is a chronological list of passes. Daylight and Night Passes are provided. The direction and elevation for each event are included in the set times for each pass. The small clock icon is beside an event. The Center icon can be used to see a satellite's location in the sky. You will be in space next to a 3D model of the satellite. SkySafari's basic versions limit the number of satellites to 125. The Plus and Pro versions track a lot of them.
Keep looking up, good luck with your satellite hunting!
Chris Vaughan is an astronomy public outreach and education specialist at Astrogeo and an award-winning member of the Royal Astronomical Society of Canada. He and John A. Read published a book. You can reach him via email and follow him on social media.
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