Venus Leads A Parade Of Planetary Crescents

Venus and Regulus in conjunction this morning at the bottom of the Sickle of Leo (drawn in). This is very close to their appearance with the naked eye. Regulus is “stuck” on top of Venus. Photo: Bob King

Once the goo was out of my eyes I could see it was a bright, clear morning. Venus dazzled in the east between a cluster evergreens, but where was Regulus? The bright star and brighter planet were in conjunction before dawn and so close at first I didn’t think I’d be able to cleave them without binoculars. Not true. Looking more closely I discovered Regulus was easy to see atop Venus. But they were tight! Rarely does a planet approach a bright star this close and seeing them together held my gaze for minutes.

Regulus sits atop Venus in this telephoto view. Details: 70mm lens at f/2.8, ISO 800 and 8-second exposure. Photo: Bob King

The night before, students in my community ed class savored double stars through the telescope. Venus and Regulus snugged up to create a similarly beautiful if temporary double, no telescope required. I hope some of you were also out at dawn this morning to enjoy the sight.

Miss the event? Mark your calendar for a close conjunction of Venus and Saturn on November 26 and 27. The two planets will be less than one degree apart both mornings. This two-planets-for-the-price-of-one promises to be a wonderful sight in a small telescope.

The waning gibbous moon shone high in the southwest this morning. In a week it will have slimmed to a thin crescent and hunker down near Venus. The crescent phase is a favorite of many sky watchers. Two points or cusps at the end of a Cheshire Cat grin make it a pleasure to the eye. Because Earth orbits outside the orbits of Venus and Mercury, we’re able to look inward toward the sun’s general direction and watch these worlds change phase like the moon. Through a small telescope, Venus and Mercury wax from moon-like crescents to “full moons” and back again.

Human eyes never saw the outer planets as crescents until our space probes gave us an otherwise impossible perspective. Credit: NASA photos taken by Voyager and Cassini

Not so with the outer planets. They can never pass between Earth and the sun, so we only see them as full or nearly full disks. It took space probe missions to the outer planets to finally “get behind” these worlds, look back toward the sun and photograph them as crescents.

The Voyager 1 and 2 spacecraft zoomed by four of the outer planets – Jupiter, Saturn, Uranus and Neptune –  and sent back breathtaking pictures shot from a viewing geometry not possible from Earth. Cassini, which is still employed at Saturn, has done the same.

A thin crescent Mars (white) captured by Rosetta probe in February 2007 during its long journey to comet Churyumov-Gerasimenko. Nightglow in the planet’s atmosphere can be seen at the 11 o’clock position. The red and fuzzy blue haloes are a result of internal reflections within the camera’s optics. Credit: ESA / MPS / UPD / LAM / IAA / RSSD / INTA / UPM / DASP / IDA / processed by E. Lakdawalla

The European Space Agency’s Rosetta probe, en route to an encounter with Comet Churyumov-Gerasimenko in the summer of 2014, made a rare flyby of the planet Mars in 2007. While trying to capture a picture of nightglow in the planet’s atmosphere, it shot a rare photo of a crescent Mars.

The pass by Mars was the second of four planetary flybys performed to crank up the craft’s speed and slingshot it to the comet. The other three gravitational boosts were provided by Earth.

This isn’t the first photo of Mars as a crescent – that was taken in December 1971 by the Soviet Mars 3 mission – but images of the Martian crescent are few. Rosetta mission controllers planned this one to study the weak light emitted by molecules in Mars’ atmosphere similar to airglow on Earth.