Summary
Introduction
Throughout history, people have always been captivated by celestial objects like stars, planets, and the Moon. Now, man-made satellites have entered the picture. Did you know you can see many satellites with the naked eye? Try this activity and find out for yourself! You will even learn how to classify them!Materials
- Place to sit and observe the sky, preferably in a rural area where light pollution is low
- Clear night
- Compass or app that indicates the cardinal direction
- Access to the internet
Prep Work
- Access a web page that displays the satellites in the sky over your area. In-the-sky.org is a good example. If your goal is to see the International Space Station (ISS)— one of the easiest satellites to see from Earth—look up good sighting opportunities in your area on NASA's Spot the Station.
- On whichever webpage you choose, enter a large city near the place where you plan to observe the sky. Any city within a 50 mile radius is fine.
- To start, look for satellites with a magnitude three or lower (a negative number is fine). A lower magnitude indicates a brighter object in the sky. Once you become experienced, you might be able to detect fainter satellites.
- Search for a time when you might observe several satellites. Try within a window of a few hours after dawn or before dusk. During this time, the satellites are still illuminated by the Sun and stand out against the dark sky.
- Look for satellites with an altitude between 20° and 90°. The altitude indicates the height above the horizon where 0° means at the horizon and 90° means directly overhead.
- Take notes on where (cardinal direction and altitude), at what time, and with what brightness (magnitude) you can expect to see some satellites cross the night sky.
Instructions
- Go to the planned location at the planned time. Make sure to bring your notes, a pen or pencil, and a compass or compass app. If you have internet access, you can look up where and when to look for a satellite onsite.
- When the time to see a satellite comes close, look in the cardinal direction where you expect to see this satellite appear. A compass can help you find N, E, S, and W. Apps can help with this step, too.
- To find the altitude, hold your arm straight out horizontally, then raise it until it is halfway between horizontal and pointing straight up.
- If you are looking for a satellite with an altitude between 35° and 55°, keep your outstretched hand as is.
- If the altitude of the satellite is below 35°, lower your outstretched hand by about 10 cm (child) / 15 cm (adult).
- If the altitude of the satellite is between 55° and 75°, elevate your outstretched hand by 10 cm (child) / 15 cm (adult).
- If the altitude of the satellite is close to 90°, raise your arm so it points straight up to the sky above you.
- Scan the area of the sky in which your arm is pointing for objects with a steady brightness that follow a straight path across the sky with consistent speed. If you spot a blinking object, it is most likely an airplane; satellites sometimes flash, but not often.
Do you see any lights that slowly move across the sky? How long does it take for them to move across the sky? - Determine the direction of the satellite's apparent movement.
Does the satellite move with the Earth's rotation (from west [W] to east [E]), against the Earth's rotation (from E to W) or at about a right angle with the Earth's rotation (following the north [N] -south [S] line)?
- Count how many satellites you can spot during your observation time, and keep track of how many move with, against, and at a right angle to the Earth's rotation.
Do most satellites move with the Earth's rotation? Why would that be the case?
What Happened?
Satellites do not have their own lights that make them visible in the night sky. We can see satellites because sunlight is being reflected off of them, just like we see the Moon in the night sky because sunlight is reflected from its surface. As satellites fly high above the Earth, from 180 to 36,000 km (112 to 22,000 miles) above Earth, the Sun still reaches them a few hours after dusk and a few hours before dawn. That is when you can spot them in the sky. The larger the reflective panels on a satellite and the lower it orbits, the easiest it is to spot.
Likely, most of the satellites you spotted were flying from west to east, in the same direction as Earth's rotation. This is partially because launching a satellite that orbits with the direction of Earth's rotation requires less fuel. These orbits are called prograde orbits. Orbits against the direction of Earth's rotation are called retrograde, and orbits that pass above or nearly above both poles are called polar orbits.
If it was hard for you to spot satellites, check out NASA's Spot the Station for opportunities to see the International Space Station (ISS) pass by. This is a very bright satellite that orbits relatively low.
You might have noticed an illuminated line moving across the sky. In 2020, a number of small satellites were launched, some of which follow each other like a train of satellites. These collections of satellites can be seen with the naked eye and appear as a line rather than a set of individual moving lights.
Digging Deeper
A satellite is an object that orbits (circles around) a planet or star. Because Earth orbits the Sun, it is a satellite. So is the Moon because the Moon orbits Earth. These are natural satellites. The word "satellite" is more often used to indicate man-made machines that orbit a planet (e.g. Earth) or a star.
There are now thousands of man-made satellites orbiting Earth. Navigation (e.g. GPS), communication, studying the weather, climate, and environmental monitoring are just a few areas where satellites play an essential role. Each satellite's purpose will help determine its best-suited orbit.
There are different ways to classify satellite orbits. Whether they travel with (prograde), against (retrograde), or at a right angle (polar) to the object's own rotation is one classification. A more common classification for satellites that orbit Earth is one that uses the height at which the satellite orbits. Orbits are classified into high Earth orbits (more than 36,000 km above Earth), medium Earth orbit (between 2,000 and 36,000 km above Earth), and low Earth orbit (between 180 and 2,000 km above Earth).
You may have heard of geosynchronous satellites. These satellites stay fixed above one spot on Earth. They orbit around 36,000 km (22,000 miles) above Earth and move with the same rotational speed as Earth itself. Because they are so high, they look faint to us. Even if we could see the light reflected from these satellites, we could easily mistake them for a star, as they stay in a fixed position in the sky.
Ask an Expert
For Further Exploration
- Try to identify other celestial objects in the night sky.
- Imagine what Earth would look like seen from one of the satellites, then look at a live stream video of Earth taken from the ISS.
