Can You See the ISS with a Telescope?

The International Space Station (ISS) is the largest human-made object to fly in outer space and, at the right time, it can be seen from anywhere around the world.

This massive space station hovers 250 miles above the surface of the earth, traveling at a speed of around 17,500 mph. It spans 357 feet in length - just one yard shy of an American football field.

The ISS serves as a large space laboratory and has been continuously inhabited since Nov. 2, 2000. An international crew of six people live and work onboard the ISS while traveling at a speed of five miles per second.

That means they orbit Earth about every 90 minutes - that's 16 orbits of Earth every 24 hours, traveling through 16 sunrises and sunsets.

You might be surprised to find out that you can see the ISS without a telescope. The ISS is as bright as Venus - the third brightest natural object in the sky. Like the moon, the brightness of the space station is owed to the sun, as the station reflects its light.

Whereas the moon can occasionally be seen during the day, the ISS can only be glimpsed during dawn or dusk, and cannot be seen when it is flying through Earth's shadow since there is no sunlight for it to reflect down to Earth.

How to See the ISS

However, while the space station is always orbiting Earth, getting a good view of the station also requires the right conditions and a small amount of planning.

Catching a glimpse of the space station hinges on its orbit and what time of day it passes overhead. The easiest way to work these specifics out is by checking online or on a smartphone app, which notifies onlookers when the ISS will be visible.

NASA’s Spot The Station website lists every time the ISS will be visible at a specific location over the next fortnight. Each time the station passes overhead is different.

On some passes, it is very dim and is only visible for a few moments, while other times it shines incredibly bright and is visible for over five minutes - allowing you to get a good glimpse.

If you’re planning to view the ISS, it’s best to do it on a night when it will be in the sky for a longer period. Not only are these passes brighter, but the station will also be visible higher in the sky.

You can also check the AccuWeather Astronomy weather forecast to see how cloud cover will impact your viewing conditions.

Viewing the ISS with a Telescope 

As we said, you can view the ISS with the naked eye, but if you want an even better look at it, you can use a telescope. Not only this, but those with a good telescope and proper equipment can look for it when it passes across the face of the moon or sun, which is known as a transit.

During the total solar eclipse in 2017, some astrophotographers traveled to very specific locations in the US to capture the ISS as it transited the sun during the partial phase of the solar eclipse.

Viewing the ISS in transit takes some planning and may even require some travel. You also need to get the timing right, as the space station will fly across the face of the sun or moon in the blink of an eye, so if you don’t time your viewing, you could miss it completely.

You also need to bear in mind safety when viewing the ISS as it transits the sun. It’s extremely important to ensure you have the proper safety equipment, as looking at the sun through a telescope without a proper solar filter is extremely dangerous and can even lead to permanent eye damage.

Tips for viewing the ISS 

  1. Choose a day: choose a good time to view the station, ideally when the ISS is visible for a few minutes at a time. Ideally use a website that allows you to enter your address, city, and zip, so you can get precise details about the best location near you to view the ISS. 
  2. Choose a good time: Usually, the best time to view the space station is at night, within a few hours of sunset or sunrise, as this is when the ISS is easiest to see. Some charts available online may provide the specific period the station will be visible for, while on others you may need to calculate the appearance length yourself by subtracting the start time from the end time. 
  3. Check the brightness: Use these charts to look at the brightness scale of the ISS at a given time. The brightness scale is a little odd: a negative number, such as -4, is strangely brighter than a positive number, such as +3. A magnitude of -4 to -2 is the brightest the ISS typically gets, and at peak brightness, it may even be visible during the day. -2 to +4 is usually visible at night, however, it may be difficult to see in areas with heavy light pollution. +4 to +6 is dim, and in this case, you’ll probably have difficulty viewing the space station, unless the night sky is very clear and you’re in an area with limited light pollution. 
  4. Check the weather: You want as little cloud cover as possible when trying to spot the ISS. Because the weather is temperamental and forecasts can be inaccurate, try to find an hour-by-hour weather forecast if possible, and check whether there will be cloud cover blocking your view during this time. 

Final say 

Contrary to what you might expect, you don’t need a telescope to view the ISS, as it’s as bright as Venus. With the right weather conditions and some planning, you can spot the space station with relative ease.

You may wish to use a telescope to get a glimpse of the ISS as it transits the sun or moon - but always ensure you have the correct protective equipment when viewing anything to do with the sun’s powerful rays. 

Gordon Watts
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