Telescope Image Orientation: Why Is Everything Upside-Down?

Although the concepts of “up” and “down” are a little different in space, you still might have noticed that the images through your telescope aren’t exactly what you expect them to be.

Rather than the same star layout you can spot with the naked eye, things through the lens of a telescope can look distinctly the wrong way around.

Telescope Image Orientation: Why Is Everything Upside-Down?

Looking through a brand-new telescope, you might be a little alarmed by your reverse images. But don’t worry! Your telescope probably isn’t broken. Images in a telescope often appear upside-down because of the arrangement of mirrors and lenses. 

It might take some time to get used to, but your flipped images are still a fantastic way to view the sky at night. After all, there is no “upside-down” in space!

Check out our guide to find out why your telescope is showing images reversed, and possible fixes for using the telescope on land.

Why Are Images Through A Telescope Upside-Down?

When you take your first look through a new telescope, you might be surprised to find that images aren’t the way you expect them to be. And while that shouldn’t put you off discovering the stars, it can leave you feeling wrong-footed.

However, the flipped image of a telescope is caused by the way light passes through the lenses and mirrors inside the scope, and is perfectly normal.

As light passes through the telescope, it travels through certain lenses. These lenses bounce the light towards the eye, producing an image.

However, as the light bounces through the scope and into focus, it often gets turned upside-down or back-to-front, depending on how many lenses and mirrors it has to pass through.

To fix this, more lenses can be added, but this reduces the clarity of the image.

What Telescopes Show Images The Wrong Way Round?

Not all telescopes show images reversed, and binoculars very rarely do. Those that are designed for terrestrial use will add prisms to ensure that all the objects are the right way up and the right way around.

But telescopes designed for astronomy will typically show an image flipped.

Refractor and Cassegrain are two types of telescope that are commonly used by astronomers. They both typically show images upside-down. To fix this, you can use a star diagonal alongside the eyepiece.

This will flip the image the right way up, but show it mirrored back to front. Adding an erect image prism diagonal will orientate the image in the right direction.

A Newtonian Reflector also shows images upside down. Again, this can be fixed with a star diagonal. However, doing so can ruin the focus, so we recommend learning to work with the flipped image.

How To Correct An Upside-Down Image From A Telescope

It is possible to correct upside-down images in a telescope. To do so, you need to add lenses or mirrors for the light to bounce through, so it comes to you the right way up.

A star diagonal attaches to the eyepiece, and adds a mirror that is angled at 45 degrees. When the light collected through the scope hits the mirror, it bounces at a 90-degree angle. This will show the image the right way up, but back to front.

Erecting prism diagonals work similarly. They reflect the light at a 90-degree angle, but do so through a prism. This will provide an image both the right way up and the right way around.

If you’re looking to correct an upside-down image from a telescope, then you’ll need to know which type of telescope you have. If you’ve got a refracting telescope, then you can try to correct it with the use of star diagonals and erecting diagonals.

But with a reflector telescope, it’s better to stick with the image upside-down. By adding a diagonal, the eyepiece is shifted further away from the focal point.

This will provide a dimmer, less focused image — much worse than just an upside down star!

Should I Correct The Image In My Telescope?

If flipping the image through a telescope is so easy, you might wonder why all telescopes don’t come the right way up. The reason for this is that adding more optics decreases the quality of the image.

As the light has a more complex path to travel, more of it gets lost along the way. This can produce a dull and out of focus image.

Some choose to add a star diagonal to make it easier to follow star charts. However, there’s a much easier (and more cost-effective) fix. Simply flip the star chart 180 degrees, and get star hopping. 

Once you’ve gotten used to the reversed image, you’ll find it easy to travel around the stars.

There are times when you need the image the right way up, but this is rarely necessary when looking at stars. In fact, the best reason to add a star or prism diagonal is to adapt the telescope for terrestrial use.

Although you might not notice stars are upside down, you’ll definitely spot a flipped image on Earth.

The added layers of optics have less of an effect on daytime terrestrial viewing, when there’s enough light to see clearly through the scope.

Many correct the image to make it look “right”. However, what’s the right way around for the night sky depends on where you’re standing on the planet.

The night sky in Australia will look the wrong way round compared to the night sky in the United States.

Does Space Have An “Up” And “Down”?

Images of space can’t really be “upside-down” because there is no right way up in space. Up and down is based on our perspective of gravity and how we interact with it on Earth.

And while gravity does play its role in distant planetary objects, it doesn’t provide them with an “up” or “down” as we think of it. 

“Up” and “down” change depending on where you are on the Earth. Star charts that are the right way around in one country, are upside-down when you travel to the other side of the planet.

But the objects in space remain in the same place.

How Do I Know If My Image Is the Right Way Up?

A telescope won’t try to hide the fact that an image is upside-down, so it should be clear in the instructions how the picture will appear.

Make sure you know what type of telescope you’re purchasing, reflector or refractor, to determine if a correction is possible. 

If it’s your first time using a telescope, figuring out which way the stars are meant to be can be overwhelming. Take a look at an object you know well, such as the moon, and see how it appears compared to the naked eye.

Now you can be sure if you have an inverted image, an upside-down image, or a corrected image, and you can delve into your star maps.

Final Thoughts

When you see an image upside-down in a telescope, don’t panic. It’s unlikely to be a sign that there’s anything wrong with your equipment.

Instead, it’s simply because the light has been bounced through the scope in a way that when it gets to the eyepiece, the image is flipped.

This can be corrected with a star diagonal, but many prefer the clearer image, even if it is on its head. After all, stars have no up or down!

Gordon Watts