See Crescent Venus This Valentine's Day

Venus presents a conundrum. While bright and alluring, it offers little in the way of telescopic detail. Despite my best efforts to ferret out low-contrast swirls in its ubiquitous cloud cover, I've seen nothing definitive. Other amateurs have had better success. Still, I always enjoy seeing Venus wax and wane like the Moon as it orbits the Sun, especially so when it's a crescent, my favorite phase. That's also when its shape becomes discernible in binoculars.

I aimed my 8×42 binoculars at the planet on February 9th and could easily make out a teeny-weeny sickle. The best time to observe the beacon-like object in a telescope or binoculars is when the sky is still bright, the better to tame its ferocious glare. That means you'll want to find Venus before or around sunset. This is easily done by keeping track of its location in relation to local landmarks or simply using a stargazing app to point you to it A blue sky does wonders for the planet, snapping it into sharp view and revealing the immaculate white purity of its deadly sulfuric acid clouds.

On February 12th, it's still a fat crescent 38.1″ across and 29% illuminated. Growing by more than 4″ each week, Venus will reach a maximum apparent size of 59.5″ (just shy of 1 arc-minute) at inferior conjunction on March 23rd, when it will pass just 42 million kilometers (26 million miles) from Earth. At the same time, Venus's illuminated extent wanes to a sliver-thin 1%.

Venus Valentine

Fortuitously, the Planet of Love reaches greatest brilliancy on Valentine's Day. At magnitude –4.9, it's the equivalent of crushing a 1.4-day-old Moon into a point source. That's bright! Bright enough to cast a shadow from a rural site on a moonless night. Count yourself lucky if you have snow cover. The added contrast makes it the perfect backdrop for shadow-spotting.

If you're wondering what to give your love for Valentine's Day, consider the nearest planet. In the movie It's a Wonderful Life, the fictional character George Bailey offers to lasso the Moon for his future wife Mary Hatch. Why not brandish your own imaginary lasso and "pull down" Venus for your sweetheart? (Don't forget to have a box of specialty chocolates as a backup.)

At greatest brilliancy, Venus sits midway between greatest elongation and inferior conjunction and displays the maximum amount of surface area combined with a large apparent disk. Newcomers to the hobby might assume that the "full moon" Venus would be brightest. But at that phase the planet lies on the opposite side of the Sun from Earth and displays a much smaller, 9.8″ disk that's nearly a magnitude fainter at –4.0. After it tops out on Valentine's Day, the crescent continues to grow but thins further, reducing the total surface area and causing Venus's brightness to diminish slightly.

As Venus approaches conjunction and moves closer into the Sun's line of sight, its solar elongation decreases. Before you know it, it's lost in the glow of evening twilight. The speed of the transition must be seen to be appreciated. On February 12th, the planet stands a comfortable 41° from the Sun; 2 weeks later, it shrinks to 30°. And the leash just keeps getting shorter.

Come conjunction, Venus will be steeped in solar glare 8.5° north of the Sun in the daytime sky. Most of us crescent-seekers will track it down by carefully offsetting in right ascension and declination from the Sun using a safe solar filter. Turns out that 8.5° is the maximum distance the planet can pass either north or south of the Sun at inferior conjunction, and that means a special observing opportunity.

If you live in the northern U.S., Canada, or other northern regions of the globe, Venus will be steeply inclined to the eastern horizon at dawn. Nearly all of that 8.5° elongation goes into the planet's altitude above the sunrise point, making it possible to see the planet before sunup with binoculars or a telescope. I've never observed it at inferior conjunction without the Sun in the sky, so I look forward to the unusual challenge. I'll focus more on what to expect and how best to view it at that time in a post next month.