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Starting now and for the next eight or nine months, Venus is visible in daylight. This opposition is especially good for northern hemisphere observers. Currently Venus transits the meridian and can be used for a nice latitude sight at about 3:00pm local mean time (14:21 UT +/- longitude converted to time --you figure out the sign!). Its expected altitude at meridian transit (for presetting your sextant) is co-latitude + declination and the Dec of Venus today is +16.0°). Then turn to the west and grab a Sun sight, and you have a two-body fix, fast and accurate. Example: Suppose you live near Indianapolis (chosen because of its extreme time zone issues): lat 40°N, lon 86°W. The meridian altitude should be 66° and the since the longitude converted to time is 5h44m, transit should occur at 20:05 UT.

For now, Venus in daylight still probably requires binoculars or a good sextant scope. I saw it in daylight with 7x35 binoculars a few days ago, but I could not spot it naked-eye. The planet will be significantly brighter in the next few months and easier to see. As always with Venus in daylight, it's shockingly bright when you finally lay eyes on it, but it vanishes completely if you look away. Finding it takes practice and patience.

Venus is heading towards inferior conjunction. On 13 August 2023, Venus will be nearly aligned between the Earth and the Sun. It will have the same ecliptic longitude as the Sun (the traditional definition of the conjunction event) at about 11:20:40 UT. But for this conjunction, the planet will pass well south of the Sun as seen in our sky. Its distance from the Sun at the time of conjunction will be about 7.7°. This means that it will be possible to follow Venus with a backyard telescope (carefully avoiding pointing it straight at the Sun!) right through inferior conjunction, and it will be possible to watch the slim crescent of Venus roll all the way around from pointing west to pointing east within a few days of observation.

At inferior conjunction Venus would no longer be useful for navigation. So what should be the cutoff for navigational relevance? Maybe 30° elongation for daylight sights? Perhaps 10° elongation for twilight sights?

Frank Reed

PS: I couldn't resist last night, and I asked ChatGPT when Venus would next reach inferior conjunction. It got it wrong repeatedly. I'm attaching the conversation strictly for its entertainment value. 

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