Venus to Shine Brightest On Saturday

This week Venus will be at its brightest for many months to come and hit its peak as a brilliant jewel in the sky on Saturday morning.

Due to a combination of its orbital path and amount of reflected sunlight, on Saturday (Dec. 4), Venus will shine so brightly it should be unmistakable to skywatchers with a clear morning sky.

This sky map shows where to look to see Venus on Saturday morning.

Venus is always the fourth-brightest object in the sky after the sun, the moon and the International Space Station. But it isn?t always equally bright. [Gallery: Venus photos from around the world]

As the Earth and Venus circle around the sun in their respective orbits, their changing geometry causes Venus? brightness to vary. As you might expect, it generally tends to be brighter when it is closer to Earth. However, this isn?t always true because Venus is an "inferior" planet.

Astronomers use "inferior" to mean "closer to the sun" rather than "lower in quality." So, the planets Mercury and Venus are both known as "inferior planets."

As a result of its orbit being closer to the sun than the Earth's, Venus passes between the Earth and the sun once every 584 days. This is known as "inferior conjunction," and last occurred on Oct. 29.

Even though Venus was closest to Earth on that date, it was ? for all intents and purposes ? invisible. That's because on Oct. 29 Venus was almost entirely backlit, except for a tiny amount of sunlight leaking through its upper atmosphere.

But over the last five weeks, Venus has moved along its orbit such that, while it is farther from the Earth than it was in late October, it is now more brightly illuminated by the sun from the side. This makes more of Venus' cloud tops visible and gives the planet a brilliant shine.

On Dec. 4, these two factors balance out to result in Venus being the brightest it can be. Astronomers measure brightness using a term called magnitude. The lower the number of an object's magnitude, the brighter it is in the sky.

This Saturday, Venus will have a magnitude of minus 4.9, while the sun is minus 26.8, the moon is minus 12.7, and the brightest star Sirius is minus 1.4.

When Venus is this bright, it is easily seen in a clear blue sky with the naked eye, if you know precisely where to look. The best way to find it is on the day when it is closest to the moon, since it?s much easier to find the bigger brighter moon in a blue sky.

A good example was yesterday morning ? Thursday, Dec. 2 ?  around 9:30 a.m. ET, when both the Moon and Venus will be due south (for observers in the northern hemisphere) and Venus will be 7 degrees (1 binocular field) above the moon.

You can find Venus first with binoculars, and then try to spot it with your naked eye. If you miss it this time, you can try again on Dec. 31.

In binoculars or a small telescope, Venus now appears as a narrow crescent, similar to the moon. In fact, if you checked the pre-dawn sky on Thursday morning, you may have seen the 26-day-old moon right next to Venus, while both showed almost the same phase illumination, since both were being lit by the sun from about the same angle.

• Gallery - Venus Seen From Around the World
• Telescopes for Beginners
• Brilliant Venus May Prompt 'UFO' Sightings

This article was provided to SPACE.com by Starry Night Education the leader in space science curriculum solutions.