View the Thin Crescent of Venus

By: Bob King July 26, 2023 11

With Venus approaching inferior conjunction in August, here’s a foolproof way to follow its thinning crescent as the planet transitions from Evening Star to Morning Star.

Venus cusp extensions — Around the time of inferior conjunction we face the nightside of Venus. Sunlight scattered by its atmosphere forms a narrow, glowing ring around the entire planet. These photos were taken on May 31 (left) and June 2, 2020, when just 0.4% and 0.1% of the planet, respectively, were illuminated by sunlight.
*Sebastian Voltmer*

Have you seen Venus lately? In late spring the brightest planet beamed high above treetops and apartment buildings alike. By the start of July, it started losing altitude — fast! Now, in the final week of the month, I have to drive 2 miles to a nearby field and use binoculars to pull it out of the twilight glow minutes after sunset. Every day the fleeing planet draws 1° closer to the solar glare as it approaches its August 13th inferior conjunction with the Sun.

In astronomy appearances can be so convincing that it's hard to explain to newcomers that Venus and the Sun aren't actually getting closer to each other. It looks that way because we can't sense depth at the distances of the Moon and planets. The sky is like a flat drawing board with celestial objects describing lines and arcs that approach and sometimes touch as if there were no space between them. Thank goodness for all that emptiness or the universe would be in a lot of trouble.

What's really happening is that Venus will soon be in the same line of sight as the Sun, then it will pass to its "right" and reappear in the morning sky. Just like someone seated a few rows ahead of you at a concert momentarily blocks your view of the lead guitarist when they get up to leave and have to excuse their way down the row.

Venus 2023 2024 — Because Venus orbits the Sun interior to the Earth it appears to cycle from one side of the Sun to the other from our perspective. At inferior conjunction Venus passes almost directly between the Earth and Sun. At superior conjunction it aligns with the Sun on the far side of its orbit. The planet's phase changes as the angle Venus makes with the Sun and Earth varies across its orbit. Venus also appears considerably larger (up to 65″) when it's closest at inferior conjunction compared to 10″ at superior conjunction.
*Bob King*

Venus currently shines about 25° east of the Sun and sets about 45 minutes after sundown. On August 13th the two bodies will be in conjunction and rise and set together. For about a week before and after that date, Venus will be difficult-to-impossible to see with the naked eye because of interference from solar glare but remain visible in a telescope if you know exactly where to look.

The orbit of Venus is tipped 3.4° relative to the plane of the ecliptic. At inferior conjunction, when the two planets are closest, Venus can pass up to 8.4° north or south of the Sun. If Venus lies at or close to either one of its nodes — the two points where it intersects the plane of Earth's orbit — we'll see it transit across the Sun's face. That last happened in June 2012 and will happen again in December 2117.

Venus color shimmers — On January 8, 2022, a 0.3%-illuminated Venus displays cusp extensions and lots of distortion and color due to unsteady air and atmospheric refraction. The crescent was so thin it behaved more like a twinkling star.
*Michael Karrer*

During the present apparition, Venus will pass 7.7° south of the Sun's center, close to its maximum distance, making it possible to safely follow the planet up to and beyond solar conjunction. This only happens occasionally. For instance, during the June 2020 conjunction, Venus sat just 0.5° north of the Sun — much too close to safely view. At its last conjunction in January 2022, the Sun and planet were less than 5° apart.

Venus crescent rollover — Around the time of inferior conjunction on August 13th you can watch the Venusian crescent flip-flop from one side of the disk to the other. North is up. Cusp extensions should also be visible around this time.
*Stellarium*

Special viewing opportunities await prepared observers every time the planet steps in front of the Sun. For one, we'll get to see the planet as a razor-thin crescent so fragile in appearance that it will appear to shimmer and possibly exhibit flickering bits of color due to atmospheric refraction. If you start looking several days before conjunction and continue looking until several days after, you'll witness the crescent "roll over" from the western to the eastern limb. Knowing that Venus is hovering in front of the Sun as this happens makes it easier to imagine the scene in three dimensions.

Venus July 24, 2023 — On July 24th the planet was 11.7% illuminated with a thinning crescent 48.5″ across.
*Shahrin Ahmad*

Then there are the cusp extensions. Instead of each crescent tip terminating in a knifelike point, the horns extend faintly beyond 180°. In past apparitions I've seen them reach two-thirds or more around Venus's limb; on rare occasions, they even touch to make a complete ring. Sunlight streaming in our direction grazes the planet's thick carbon dioxide atmosphere and faintly illuminates the planet's otherwise dark limb. At this conjunction 0.9% of the planet will be illuminated at minimum, enough to see the tip extensions, but the full circle may prove elusive.

If you have a Go To mount, finding the pointy planet is easy enough. If not, you'll need an equatorially mounted telescope and a simple compass. I look up the celestial coordinates of the Sun and Venus, aim my solar-filtered telescope at the Sun, offset in right ascension and declination, pull the filter and if I'm lucky I see Venus smiling back. My favorite instrument for daytime Venus viewing is a 94-mm refractor on an equatorial mount. Only modest magnification is needed. I start at very lower power (32×) for a wide field of view, the more easily to snag the planet. Then I increase magnification to 65× or 90× to better coax out the cusp extensions.

Crescent Venus — Looking like a second moon, albeit a tiny one, Venus shows off its pointy form through a 600-mm telephoto lens at dusk on July 16, 2023.
*Bob King*

With Venus so close to the Sun, it's important to take the necessary precautions to avoid looking directly at the blazing solar surface. Even a momentary glimpse can risk eye damage so please be careful. Work slowly and deliberately. If the sky looks too glaringly bright near the Sun, use sunglasses or a red filter (which also increases contrast) to temper the glare. A dew shield over the objective end of a refracting telescope will help keep sunlight and solar reflections out of the field of view. Make one from dark-colored cardboard if your scope is lacking.

Let's take this step by step:

Step 1: Find the Coordinates

Venus and Sun coordinates — I use an app (SkySafari here) to find the current right ascension (R.A.) and declination of the Sun and Venus. If you don't have an app then download the free Stellarium skywatching program for your PC or Mac laptop and simply click on the Sun and Venus for their celestial coordinates at the time of your observation. My date of observation was July 22, 2023.
*Bob King*

Step 2: Find the offset

Venus-Sun offset — Once you know the R.A. and declination of the Sun and Venus, find the difference between them to determine how far east / west and north / south you need to move the telescope from the Sun to land on Venus. A simple subtraction gave the following offset for July 22nd: 1h 50m in R.A. to the east and 11.5° south in declination.
*Bob King*

Step 3: Align the Mount

Polar axis alignment — Use a compass to point the polar axis of your equatorial mount north. At some locations there's a considerable difference — called *magnetic declination* — between magnetic north and true north. If it's more than a few degrees you'll have to factor in the difference to ensure the axis points to true north and not magnetic north. Check it with this magnetic declination calculator. You can also use your cell phone's compass. *Bob King*

Step 4: Center on the Sun

Pointing at the sun — Cap the end of your scope with a safe solar filter, cover the finderscope, and center on the Sun. Focus sharply.
*Bob King*

Step 5: Offset the telescope

Sun to Venus offsets — Unlock one axis at a time and offset the correct amounts in R.A. and declination from the Sun to Venus.
*Bob King*

Step 6: Remove the Filter and Look for Venus

Found it! — Remove the filter and look through the eyepiece. If you've been meticulous Venus should pop into view. Don't see it? Check the finder. Still don't see it? Go through the process again. It usually takes me two tries.
*Bob King*

Once you get the hang of calculating offsets, you'll have the distinct pleasure of seeing Venus at the forbidden time of solar conjunction and maybe even experience a dizzying sense of depth perception.

Comments

Mike McCabe

July 26, 2023 at 12:08 pm

Hi Bob,
Excellent article, as usual! One advantage to today's cell phones is that most of them can be set up with a compass that actually points to true north, thereby eliminating the step of figuring out the magnetic declination. My daytime polar alignment has improved exponentially since the advent of the compass app!
Sincerely,
Mike McCabe

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Bob KingPost Author

July 26, 2023 at 1:01 pm

Thank you, Mike. And that's an excellent suggestion on the compass app — thanks!

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Joe Stieber

July 26, 2023 at 4:06 pm

After many years of being foiled by uncooperative weather, I was finally able to spot Venus on the day of inferior conjunction, January 8, 2022, when it was about 4.8° from the sun, center-to-center, using my 88 mm apo spotting scope. In addition, I spotted it at sunrise and sunset that day with 15x56 binoculars, thanks to its northerly ecliptic latitude. The crescent was beautifully thin in the scope at 60x.

I didn't think it would be possible to see Venus at superior conjunction on October 22, 2022, when it was a mere 1° from the sun, center-to-center, but I started looking a couple of weeks beforehand anyway. I continued my vigil and was able to pick it out on the day of conjunction with the 88 mm scope Since it was superior conjunction, Venus was just a small "full" disc, a bright spot of light vs. the lovely large crescent at inferior conjunction.

My standard procedure for these daytime sightings is to use the spotting scope on a sturdy tripod, sitting behind it on an ordinary lawn chair. I don't use any filters, but the important thing is to BLOCK THE SUN behind something opaque. I use a solar panel on a utility pole at the local baseball field complex. Those panels, ubiquitous here in southern New Jersey, are about 4 ft high x 6 ft wide and are mounted at an angle, around 15 ft off the ground. I'll set up the tripod-mounted scope in the shadow of the panel and sit on a lawn chair behind it. As time progresses and the sun moves, I'll move the tripod and chair as needed to keep the sun blocked.

At conjunction, the location of Venus relative to the sun is easy to judge since they're close together. I'll look at a planetarium app to get the angle and distance for the current date and time and use that to estimate the solar offset and scan while pushing the scope manually in the estimated direction (it's on an alt-azimuth mount, and I also do all my nighttime observing with alt-az manual pointing).

Of course, seeing Venus isn't always easy. Even on a really clear day, the glare from the sun extends beyond the solar panel, and oftentimes, flying pappi (plural of pappus, a wind-borne seed), sometimes a blizzard of them, add visual confusion. Those seeds do provide a very graphic example of forward scattering (a phenomenon sometimes associated with comets near the sun). Look away from the sun and they disappear.

However, my best sighting of Venus was on June 1, 2020, two days before inferior conjunction when Venus was 3.1° from the sun. The crescent was sublimely thin and in moments of good seeing, the illumination continued for the full rim of the disc. That may be the most magnificent thing I've ever seen in a telescope and the view was never matched by any photos I've seen of Venus near inferior conjunction! Then we had a spell of cloudy weather.

Of course, I'm following the end of this Venus elongation. I last saw it on July 24, 2022, around sunset (it was cloudy last night, July 25). The crescent was evident with my 15x56 binoculars as it had grown to nearly 49 arc seconds diameter and is now down to about 9% illumination. Soon, I'll be looking during the daytime.

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Bob KingPost Author

July 28, 2023 at 11:07 am

Hi Joe,
Beautiful description of seeing the planet Venus so close to the sun. It IS a sublime experience to see that impossibly delicate crescent reaching around the planet.
Even though Venus will appear slightly thicker at this conjunction than in 2020 I'm eager for the sight. Oh, and I'm familiar too with those fluffy seeds — a great example of forward scattering and also a little infuriating when attempting to get your eye focused on the planet!

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Anthony Barreiro

July 26, 2023 at 6:45 pm

Thank you Bob. I've been enjoying seeing crescent Venus in the afternoon through 10x42 image-stabilized binoculars. My back yard is on the east side of the two-story building I live in, so I wait until the back yard is shaded in late afternoon. I calculate the offset from the Sun, guesstimate where Venus will be, and scan around until I see her. After a few clear days in a row I know about where she will be relative to my neighbor's roof deck.

When the evening will be clear I take a little 50 mm spotting scope up to Bernal Hill to show passersby crescent Venus from just after sunset until twilight gets too dark and the shape is lost in the glare. The correct image in the spotting scope makes it easier to explain the geometry of why we see a crescent. Plus it's tiny and easy to carry on a mile walk from my home and up the hill. Last night was remarkably clear and pleasant, there were a lot of people out walking on the hill. Venus, Mercury, Mars, the waxing quarter Moon, M7, and M8 were lovely.

I've never tried to see Venus at inferior conjunction (other than the 2012 transit, which I watched from Hawaii). I would think people in the southern hemisphere will have an easier time observing this year's inferior conjunction. They'll be able to situate themselves south of a building to block the Sun, with Venus passing higher than the Sun. For us northerners, Venus will be below the Sun, which will be trickier. I wish good luck and safety for all who try.

In Sumerian and later mythologies, the planet we call Venus was considered the goddess Inanna. The passage from evening to morning star is Inanna's heroic journey through the underworld, death, and rebirth.

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Bob KingPost Author

July 28, 2023 at 11:10 am

Hi Anthony,

Thank you for your comment. The folks in your part of the world are lucky to have you. Sharing the beauty of the cosmos is good in every way. Good point about southern hemisphere vs. northern!

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Ludovicus

July 28, 2023 at 5:55 pm

Don't forget the power of a good Alt-az mount!!!

Been bagging daytime planets and Mercury/Venus closer proximal views with big binoculars as well, and scopes! A good digital inclinometer on an RDF rail mounted works wonders! For those interested, email: [email protected]

Caught Venus really nicely in my 90mm APO using my house as a "block" when Venus was <5% lit - caught a dandy image of it too. 🙂

Just be safe and midful of the solar proximity, as Bob mentions. All fine then!

DH,
Edmonton AB Canada

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Glenn

July 28, 2023 at 9:23 pm

With Venus nearly 8 degrees south of the sun they cannot rise nor set together. Using heavens above: on Aug 12 from Sydney Venus rises at 6.21 am and the sun at 6.42 am. Setting is 5.20 and 5.39 pm respectively. At the moment we southerners are favoured with sunset tonight at 5.10 pm and Venus sets at 7 pm so it is still easy in a deep twilight sky at 6 pm.
Venus is now retrograding since it was stationary on the 20th July, so nearing the sun at more than 1 degree per day. At Inferior Conjunction they move apart relatively at 1.75*/day.
The orbital resonance of Venus and Earth means we will have almost identical circumstances in 8 years. And every 32 years Mars is involved as it was a month ago with the M and V quasi conjunction. Back in 1991 there were two proper conjunctions.

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Bob KingPost Author

July 29, 2023 at 12:56 am

Hi Glenn,

I only meant they rose and set together in a generic way "as a pair." But yes, they definitely rise and set at somewhat different times. Good to know about the 32-year Mars period. Had no idea! Thank you.

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Bob KingPost Author

July 29, 2023 at 12:54 am

Ludovicus,
Thanks for chiming in about using an alt-az mount and offering to share your technique.

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Andrew James

July 31, 2023 at 2:19 am

Instead of posting your comment, readers might like to look at this webpage about observing Venus in a telescope. e.g. http://www.southastrodel.com/PageVenus002.htm . One of the interesting observations that you can make use of the ashen light, which is the light you can see on the dark portion of the planet. You can also use a purple filter especially useful to improve contrast with the background sky.
One of the first serious observers that made very close observations of the Sun and either Mercury or Venus, was the French observer, Jacques Vidal who lived in the French town of Mirepoix between 1790 and 1805. He made 170 observations in this time, and it was important to accurately determine, especially, the eccentric orbital elements of Mercury. One of his observations was just 15 arcmin from the Sun's surface! The famous French astronomers Lalande and La Verrier at the Paris Observatory, thought he was remarkable and extraordinary, and gave tributes and fanfare to his extraordinary skills.
I have done this kind of observation in the past probably six or seven times, but I would advise any novice to be ultra-careful so close to the Sun. I would strongly advise that if you do attempt this, make sure before you look at the sun is not in the eyepiece field by looking at the lens surface before looking into the eyepiece. Even better, is make sure the telescope out is firmly stuck to the ground, and that there is no possibility of accidentally knocking the field of you into the rays of the sun. Even then, this is not for the faint hearted nor even if experienced!

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