Sharing the Sky, April—May 2020

by Jeffrey Pinyan

April marks the opening of our 2020 season. We have about 30 Fridays ahead of us, and as long as the weather cooperates, we’ll have some special celestial treats to share with the public.

Venus and the Seven Sisters – Apr 1-5
Peaking on April 3rd (the first Friday of our season), Venus makes her way through the Pleiades. Venus, even half-lit, is hundreds of times brighter than the individual stars that make up this Dipper-shaped cluster. Because this conjunction occurs early in April, the skies will be dark enough to enjoy it before both Venus and the Pleiades set behind our observatory’s southwestern tree line. Continued observing until around 11 PM can occur out at the soccer fields.

This stunning April conjunction comes in three varieties, each of which repeats every eight years. This cycle (2012 – 2020 – 2028) occurs early in the month and has Venus passing directly through the Pleiades. Another cycle (2015 – 2023 – 2031) peaks near mid-April and has Venus pass some 2.5° south of the cluster; the third cycle (2018 – 2026 – 2034) peaks late in the month and is the most distant, about 3.5° south. The close encounter is due to the Pleaides’ location about 4 degrees north of the ecliptic, and Venus’ 3.4° tilt relative to that same plane. The cause of the reliable cycle is the orbital resonance between Venus and Earth: the two planets align 5 times every 8 terrestrial years (= 13 Venusian years). The 13:8 resonance might remind you of the Fibonacci sequence; indeed, the actual resonance ratio is less than 0.5% from the golden ratio Φ (phi), that value toward which the ratio of two successive Fibonacci numbers approaches (3/2, 5/3, 8/5, 13/8, 21/13, and so on)…

Planetary Close Passes – Apr 14-16
If you’re up around 5 AM on these three successive mornings, you can watch the waning Moon go from gibbous to crescent while skirting close to Jupiter, Saturn, and Mars. These are all low in the southeast (dropping from 20° to 12° in altitude) so you’ll need a low horizon, and you’ll have to act fast before the encroaching dawn drowns them out.
Unfortunately for us in New Jersey, the closest approach to Jupiter happens when both are well below the horizon (7:30 PM on the 14th), but Saturn will be a mere 3° above the Moon just before sunrise on the 15th, and Mars will be about the same at 5 AM on the 16th.

PANSTARRS at Perihelion – May 4
Comet C/2017 T2, also called PANSTARRS, will make its closest approach to the Sun at the beginning of May. Its position near the north celestial pole means it will be visible all night long. The current estimate for its brightest magnitude is 7, meaning it will be too dim for the naked eye.

It might be a worthy target for displaying to the public this month, especially with the long-exposure setup on the observatory’s permanent telescopes. Find it among the dim stars between Ursa Major and Camelopardalis, around 76° dec., and 06h20m r.a. (May 1st) to 09h0m r.a. (May 15th).

Jupiter Bids Saturn Adieu – May 18
Early on this Monday morning (4 – 5 AM) you can spot Jupiter and Saturn in the south-southeast, around 4.7° apart. These two gas giants have been creeping closer and closer together all year, as Jupiter has appeared to be trying to overtake Saturn. But on May 18th, Jupiter enters its retrograde motion and will begin slipping further west of Saturn. This will continue until the beginning of September, which marks the beginning of a 3½ month charge toward a stunning solstice conjunction on the evening of December 21st.

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