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.
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 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.
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.
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.
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.
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
Step 2: Find the offset
Step 3: Align the Mount
Step 4: Center on the Sun
Step 5: Offset the telescope
Step 6: Remove the Filter and Look for Venus
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.