Viewing Venus Through a Telescope

Most people who get their first telescope will spend their first nights looking at the Moon. And the Moon is certainly a worthwhile target. But it is the planets that usually draw their attention next.

This guide will be about observing Venus with a telescope, the second planet from the Sun, the nearest planet to us, and the third brightest object in the sky. When Venus is in the sky, it is brighter than any star or indeed any other celestial object besides the Moon and Sun. Venus is visible in broad daylight on an exceptionally clear day to the naked eye. Venus appears like a tiny gibbous or crescent Moon through a telescope, and the discovery of its phase was key to our modern understanding of the Universe.

The Italian astronomer Galileo Galilei is credited with the discovery of the phases of Venus in the 17th century, a key piece of evidence supporting the Copernican model of the Solar System, which states that the planets, including Earth, go around the Sun instead of all of these celestial bodies orbiting the Earth as current dogma supports. Using Galileo’s telescope, he observed that Venus, similar to the Moon, undergoes a full set of phases. This observation was inconsistent with the geocentric model, which predicted that Venus would always appear in a crescent or new phase. Instead, Galileo’s observations revealed that Venus could also be seen in full and gibbous phases, thus supporting the heliocentric model where Venus orbits the Sun, not the Earth.

However, Venus is not always in the sky. As it orbits around the Sun, moving behind the Sun, it moves out of our view. Venus, like Mercury, is closer to the Sun than Earth. The result of this is that it is never far from the Sun, from our vantage point. In fact, it is never more than around 47 degrees away.

When To See Venus In The Sky?

Because of its proximity to the Sun, Venus is highest in the sky during the twilight hours, earning it the nickname “Evening Star” when it appears after sunset and “Morning Star” when it shows up before sunrise. Look for a bright, yellowish object that doesn’t twinkle or move—that’s Venus or Jupiter most likely. Smartphone apps and online tools can help you pinpoint Venus’s exact location from your viewing location. Once you’ve found it, it’s effortless to locate Venus again each night and track its progress as both Venus and Earth move around the Solar system with respect to each other.

The picture below is a screen capture from the Stellarium program, which is a sky tracking tool. It depicts the sky on February 10, 2020, just as an example, so I can explain how to find Venus.

Notice that the direction we are facing is 180 degrees, or directly South. There is an orange line shown across the image, the Ecliptic line. This is the path across the sky traveled by the Sun, moon, and all of the planets. Notice that Venus is shown on the Ecliptic.

The Ecliptic is always along the southern sky. So, if you are looking for Venus or any of the planets, watch the paths traveled by the Sun and Moon, and you will know where to look. Now it is just a matter of knowing when to look and where to be on the Ecliptic to find them.

Elongation & Superior/Inferior Conjunctions of Venus

Venus orbits the Sun inside Earth’s orbit, so from our perspective, it rapidly emerges low after sunset, swings out to the east of the Sun in the evening sky, and then dips back towards the Sun, reappearing in the dawn sky to the west. It then swings back around and repeats this cycle every 584 days, its synodic period.

The point at which Venus is at its maximum distance from the Sun in our sky is known as its greatest elongation. At this point, Venus is positioned at the top of an imaginary line drawn from the Earth through the Sun, forming a right angle with the line from the Sun to Venus. The planet appears half-lit when viewed through a telescope, much like a first-quarter or last quarter Moon. The dates of greatest elongation are the best times to view Venus, as it spends more time above the horizon before or after the Sun and appears as a bright “evening star” in the western sky after sunset or a “morning star” in the eastern sky before sunrise. The synodic period is also the time between greatest elongations on each side of the Sun.

Upcoming dates of Greatest Elongation for Venus

• October 23, 2023 (Western elongation)
• February 25, 2024 (Eastern elongation)
• June 8, 2024 (Western elongation)

In the context of observing Venus, two critical terms are “inferior conjunction” and “superior conjunction.” An inferior conjunction occurs when Venus is aligned between the Earth and the Sun, making it appear as a large, thin crescent when observed from Earth. Conversely, a superior conjunction occurs when Venus is on the far side of the Sun relative to Earth. Around this time, Venus is not visible from Earth due to the Sun’s glare and appears as a small, nearly full disc when it can be seen emerging again in the evening sky.

Upcoming Venus Solar Conjunction Dates

Inferior Conjunction

• August 13, 2023
• March 17, 2024
• September 1, 2024
• April 14, 2025

Superior Conjunction

• October 22, 2022
• May 10, 2023
• November 18, 2023
• June 1, 2024

Finding Venus in the Daytime Sky

Surprisingly, Venus can also be spotted in the daytime sky if you know exactly where to look. The key is good transparency, the same as you’d want for any nighttime astronomical viewing. Dust, clouds, smoke, haze, and other pollutants will brighten and fog up the sky too much to spot the planet amidst a sea of blue, but even on a fairly bad day, it is pretty easy to locate Venus in binoculars or a finder scope.

The best time to try to spot Venus during the day with the naked eye alone is when it is at its greatest elongation, meaning it is as far from the Sun in the sky as it gets. Look for a small, bright speck in the sky. Using a Moon or a nearby contrail as a reference can make it easier to locate the planet. Of course, taking safety precautions to avoid looking directly at the Sun is vital when you’re looking through a telescope. Once you’ve seen Venus in daylight, it’s nearly impossible to find yourself not notice it again and again if conditions are good. If you’ve successfully spotted Venus with the unaided eye, you might also be able to go after Jupiter, which is nearly as big and bright.

What Does Venus Look Like Through a Telescope?

The main thing you will see when looking through a telescope at Venus is its phase. The planet’s dazzlingly bright (but perfectly safe to view) cloud tops easily wash out faint detail, which can usually only be observed with cameras or by patient observers with filters. The only exception is slight general light-dark contrasts, which (as of the time of writing in 2023) can be seen with even a small telescope. Observing Venus with a telescope in the daytime or equipping a good blue or violet color filter (see below) may bring out striations in the clouds. Other than that, the only possible detail you might see is the Ashen Light.

The Ashen Light of Venus is a faint illumination of its dark side observed when Venus is in a crescent phase. It was first reported in 1643 and has been a matter of controversy ever since. Some observers swear by it, while others state they’ve never seen it. The source of Venus’ ashen light is still unknown. Several theories have been proposed, including lightning, airglow, and even auroras, but none have been definitively proven. Due to the lack of a global magnetic field, auroras like those on Earth are unlikely. More recent hypotheses suggest it could be due to a form of airglow, a faint emission of light by a planetary atmosphere caused by the recombination of atoms and molecules that were ionized by solar radiation. Lightning has been theorized to also be responsible, but it would have to be much brighter than the lightning observed by scientists so far to trigger such an obvious glow.

Conjunctions & Occultations of Venus

Due to its position in the Solar System as an inner planet, Venus frequently appears in conjunction with other planets in the night sky, mainly due to its proximity to the ecliptic plane. Occasionally, these are close conjunctions where both Venus and another planet will fit in the same telescopic field of view. On February 22nd, 2024, low in the pre-dawn sky, one of these conjunctions occurs with Mars; they will appear a little less than a degree apart and in the same medium- to low-power field with a telescope. On March 21st, it passes a similar distance from Saturn but is still quite hard to spot. On April 3rd, higher in the morning sky, an even closer encounter occurs with Neptune, though spotting the latter will be difficult. The next interesting conjunction will be on August 12, 2025, when Venus approaches to within about 1 degree of Jupiter in the morning sky.

Venus also partakes in lunar occultations and conjunctions quite frequently, where the planet appears very close to our Moon or is blocked by it altogether in an occultation. These events are always a treat to observe due to Venus’ bright and shining presence in the sky along with the phases of both participants. Two particularly close approaches between the two occur in 2024, resulting in an occultation for some observers. On April 7, 2024, the Moon will appear to occult Venus low in the pre-dawn sky throughout North America; the second approach on September 5 will only result in an occultation in Antarctica.

Transits of Venus

One of the rarest predictable astronomical phenomena is the transit of Venus. This event occurs when Venus, from our perspective on Earth, passes directly across the face of the Sun, appearing as a small black disc moving across the Sun’s bright surface. These transits occur in pairs eight years apart, separated by long intervals of over a century. The last pair of transits occurred in 2004 and 2012, and the next pair won’t happen until 2117 and 2125. These transits have been historically important in measuring the scale of the Solar System as well as studying Venus itself.

Telescope Color Filters for Observing Venus

Color filters for telescopes can be helpful in enhancing your view of the planets, and this is particularly true when observing Venus, a notoriously tricky planet to study due to its intensely bright, featureless appearance. The use of color filters can help improve contrast and bring out subtle details that might otherwise go unnoticed. Normally we don’t recommend color filters very strongly – cheap ones just blur your view, and they are generally only useful in fringe cases – but if you really want to see Venusian cloud structure, a filter is one of the more effective ways to improve your luck.

One of the best, but less widely available, filters for observing Venus is the #47 Wratten “Violet” filter. This is a dark blue filter that is known to bring out the most subtle features in Venus’s cloud cover by increasing the contrast. However, this filter tends to dim the view quite significantly. Therefore, it’s most effective when used with larger telescopes, typically those with an aperture of 8 inches or more. For smaller telescopes, the dimming effect of the #47 Wratten filter is too great and a #80A filter is probably best.

The #80A filter, which is widely considered the best available for Jupiter and fairly common, is another option when observing Venus. This blue filter can help to slightly increase contrast and reduce the planet’s dazzling glare, although its effects are generally less pronounced than the #47 Wratten filter. 

Other filters, such as the #21 (orange) and #38A (dark blue) can sometimes enhance the view of Venus, but their effectiveness tends to vary and a #47 or #80A filter is probably more useful. The #21 Orange is commonly used for lunar observation in the daytime to reduce the blue filter of the sky, but the bluish tint of the daytime sky actually helps increase contrast on Venus, so you should only give this filter a try when the Sun is well below the horizon.

Neutral density filters and other color filters are largely ineffective when observing Venus. Neutral density filters simply reduce the amount of light entering the telescope without altering the colors, which, while perhaps more comfortable, doesn’t contribute to bringing out any additional detail in Venus’ cloud tops. Other color filters might have beneficial effects, but none have been shown to consistently enhance the view of Venus like the filters mentioned above.

Imaging Venus’ Surface in the Infrared

Venus emits a lot of heat because of its thick atmosphere and its proximity to the Sun, and this heat can be detected by spacecraft and telescopes with thermal imaging capabilities. Infrared light is invisible to the human eye, but it can be detected by special cameras. However, in addition to the cost of the equipment, setting up for this type of imaging can be difficult. For starters, you’ll need a camera and filters to shoot around the 1 micron (1000nm) range.

The atmosphere of Venus is very bright in the thermal/IR spectrum, and it can make it hard to see faint features on the nighttime surface of the planet. The entire daylight side will need to be overexposed. The rather long exposure time of your images also limits the ability to compensate for bad atmospheric conditions with stacking, so you need to start out with fairly good seeing conditions. Venus should be as high in the sky as possible and in a crescent phase, and you should be equipped with a fairly large telescope—10” or bigger is best.

Venus Facts

Venus is the third smallest planet in our solar system, yet it’s roughly similar in size to Earth with a diameter of about 12,104 kilometers, only about 638 kilometers less than Earth’s diameter. This similarity in size has earned Venus the nickname “Earth’s Twin”. However, the two planets have very different environments and physical characteristics.

Venus is a terrestrial, or rocky, planet, which means its composition is primarily silicate minerals and metals like Earth, Mars, the Moon, and Mercury. Venus’ crust is mostly composed of rocky basalt, and its entire surface is obscured by a thick layer of clouds composed mainly of sulfuric acid, with trace amounts of other compounds. These clouds reflect the visible portions of  sunlight, which is why Venus shines so brightly in our sky. However, they allow infrared radiation, or heat, through. This allows Venus’ crushingly thick carbon dioxide atmosphere to trap heat in a runaway form of the greenhouse effect.

Venus’ interior structure is thought to be similar to Earth’s, with a crust, a mantle, and a core. The core is believed to be at least partially liquid, but due at least in part to Venus’s slow rotation, it does not generate a significant magnetic field like Earth’s. Venus does not have tectonic plates like Earth, but it shows signs of tectonic-like activity in the form of crustal rifting and volcanism.

Due to its similar density but lower mass compared to Earth, the gravity on Venus is just slightly lower than it is on Earth, about 90% of Earth’s gravity. Specifically, the acceleration due to gravity on the surface of Venus is about 8.87 m/s² compared to Earth’s 9.8 m/s². This means that an object weighs a bit less on Venus than it would on Earth, by about 11%. You wouldn’t be able to leap over tall buildings like on the Moon, but Venus’ lower gravity would certainly improve your professional basketball stats if you could somehow build a court there.

The rotation of Venus is another intriguing feature. Remarkably slow, it takes Venus about 243 Earth days to complete a single rotation on its axis, longer than its orbital period around the Sun, which is 225 Earth days. This slow rotation contributes to Venus’s thick, dense atmosphere and extreme surface temperatures. Notably, Venus rotates in the opposite direction of most planets in the solar system, a phenomenon known as retrograde rotation.