What Can You See With a Telescope?

A lot of novice stargazers end up disappointed upon buying a telescope and taking their first peek at the interesting planets, rich star clusters and far-away galaxies. Some amateurs simply do not know what to expect, while others have a puffed up and unrealistic idea of what their observations will look like thanks to the wonderful images we see of space in the media.

From solar system views to a look at deep sky objects, this overview will help clarify what you can expect to see with your backyard telescope.

Technical and Environmental Considerations

Aperture

An instrument’s aperture size is always an important factor when buying and using a telescope. This is the size of the primary optic or main openings of a telescope. Large aperture telescopes have the capacity to gather and focus more light, so the bigger the aperture of the telescope, the more it can essentially ‘see’. While an 18 inch telescope of high quality optics will show breath-taking images, they are largely impractical for us ordinary folk. They are expensive, take up a lot of space, and cannot be handled or transported.

A safer bet for most amateur needs is a telescope of around 4 to 8 inches. Instruments of this size are practical and will get more use.

Aperture also comes in to play with another element to what you can see with your telescope: limiting magnitude.

Magnitude and Limiting Magnitude

Magnitude – or more accurately, apparent magnitude – is how bright a celestial object appears from Earth. The brighter an object appears, the lower the number assigned for magnitude will be – including negative numbers.

The Sun has an apparent magnitude of -27, the full moon of -13, Venus – the brightest planet in the night sky – can appear as bright as magnitude -5, and the brightest star Sirius can have an apparent magnitude of -1.5.

There is a limit to how dim of an object the naked eye and telescopes can see. This is called the limiting magnitude, and for telescopes, aperture will play a part in what the limiting magnitude is.

For the rest of this article, we will work on what you can see with an 8 inch telescope, though most of what is mentioned can be seen with a 6 inch telescope as well. Telescopes of this aperture can see objects as faint as magnitude 13, revealing most solar system bodies, and a variety of star clusters, nebulae, and galaxies.

As a quick note, the unaided eye can see celestial objects as dim as around the magnitude 6.5 mark, and this is for good conditions under dark skies. Apparent magnitude does vary slightly depending on certain factors, and the conditions of the sky will surely also affect what we can see. The biggest telescope won’t help much under heavily light polluted skies!

Solar System

The traditional naked eye planets – Mercury, Venus, Mars, Jupiter and Saturn – are great targets for observing through your telescope. They appear relatively bright in the night sky, so they are easy to find and can show some interesting detail under magnification. Uranus and Neptune can also be viewed with a small telescope.

Mercury

The innermost planet shows as a small yellow or pale disc. Like the Moon, Mercury and Venus appear to go through phases, which you can observe through your telescope.

Venus

VenusThe evening and morning star, Venus is the third brightest object in the sky after the Sun and Moon. A telescope shows a bright disc. The planet is covered in a thick layer of atmospheric clouds and so no surface details are visible. But like Mercury, Venus goes through phases which you can observe.

Mars

The beautiful red planet is small compared to the as giants that follow it, but a good telescope can show some wonderful details. Its distinct reddish-orange colour can be detected even with the naked eye, and the disc through a telescope shows this colour too. A telescope of 6 inches is enough to reveal the planet’s white polar caps, and a telescope of 8 inches shows fainter details like Mars’ dark markings. You can also observe Mars’ two natural satellites, Phobos and Deimos, through an 8 inch instrument.

Jupiter

JupiterJupiter is the second brightest planet in the night sky after Venus, and is the Solar System’s giant. Because of its great size and the makeup of its atmosphere, even a smaller telescope shows lovely features. The planet also has a very quick rotation, meaning that features you can observe change relatively quickly. You will be able to see Jupiter’s belts, showing as dark bands across the disc of the planet. Also look for details that show Jupiter’s storms in action. These include light zones and dark bands which are strong winds moving eastward with the rotation of the planet, and winds moving in the opposite direction respectively. And then of course, there is the magnificent Great Red Spot to behold: Jupiter’s 300+ year raging storm.

Four Galilean Moons; Io, Europa, Ganymede, and Callista are actually visible to the unaided eye when the glare of their parent planet is blocked off. Through a telescope you will be able to watch as the moons transit Jupiter (move in front of and across the planet’s disc), looking almost shadow-like.

Saturn

Saturn, like its giant neighbour Jupiter, is a firm favourite for novices and seasoned stargazers alike; and it’s no wonder with its majestic rings. Through your backyard telescope you will be able to see the rings as two bands (Rings A and B), as well as Cassini’s Division (a thin gap). Many of Saturn’s larger moons can also be viewed including Rhea, Enceladus, Tethys, Dione, Hyperion, and Phoebe.

Uranus

Though Uranus can be seen with the unaided eye under dark skies and good seeing conditions, at magnitude 5.5 it’s a bit of a challenge to see under more polluted skies and less steady conditions. Uranus shows as a small, featureless blue disc. An 8 inch telescope is able to show Uranus’ biggest moons: Titania and Oberon.

Neptune

Neptune is the furthest planet from the Sun, and is beyond the limiting magnitude of the unaided eye. It can however be viewed through your telescope, though no discernable detail can be seen. An 8 inch telescope will show Neptune’s brightest moon Titan.

Pluto and The Other Dwarf Planets

Pluto and the other official dwarf planets – Ceres, Haumea, Makemake, and Eris are too small and far away to easily see, even through your backyard telescope. Even Ceres, the brightest magnitude of the five, won’t show up with much detail. Ceres varies between the 7th and 9th magnitude.

Comets

Comets are rocky bits of dust and frozen gases that are a stunning sight to see with the naked eye, binoculars or telescopes. As comets come closer to the Sun in their orbit, the trapped gases are warmed and released, producing the awesome tail that comets are so popular for. A telescopic view will show a brightly lit and dense head, trailed by milky nebulosity. It is best observed under low magnification, so that the field of view is greater allowing you to see more of the comet at once.

The Sun

Viewing the Sun comes with a special precautionary warning: exposing your eyes to direct sunlight can leave you blinded. Never risk viewing the sun under incorrect conditions – for example, by using makeshift filters made from negative film etc. You should only ever use trusted and quality Sun filters, which cover the entire aperture of your telescope.

When done correctly, your telescope will open up an awe-inspiring solar world: sunspots, transits of Mercury and more rarely Venus, granulation and more.

Deep Sky Objects

Star Cluster Deep sky viewing generally includes celestial objects outside of our Solar System; such as nebulae, star clusters and galaxies.

Most deep sky objects appear as colourless, cloudy features interspersed by many bright points of light. Nebulae may look like fuzzy patches or wispy streaks. Galaxies will show a somewhat brighter and denser core surrounded by cloudiness. Telescopes can also resolve clusters that look like fuzzy balls to the naked eye into many points of light. Though the view is far from what you see on the internet pictures, it is truly breath-taking.

A good starting point for telescopic deep sky observations is the catalogue of Messier Objects: 110 different nebulae, star clusters, and galaxies that can all be viewed with your backyard telescope.

Conclusion

Not everything you can see through your telescope has been mentioned here. The skies are so vast that you will not have uncovered a fraction of all the beauty you can see, even after owning your telescope for many years.

Lastly, remember that even the best telescope won’t reveal much under polluted skies and bad seeing conditions, and that on the other hand cheap optics won’t help you even under perfect skies. Quality in both sky and instrument are always vital for the best observations.

Happy viewing and clear skies.

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