This month’s fun fact about the planets:

Venus

Venus is the second planet from the Sun and is Earth’s closest planetary neighbour. It’s one of the four inner rocky planets, and it’s often called Earth’s twin because it’s similar in size and density. These are not identical twins, however – there are radical differences between the two worlds.

Venus has a thick, toxic atmosphere filled with carbon dioxide and it’s perpetually shrouded in thick, yellowish clouds of sulfuric acid that trap heat, causing a runaway greenhouse effect. It’s the hottest planet in our solar system, even though Mercury is closer to the Sun.

Another big difference from Earth – Venus rotates on its axis backward, compared to most of the other planets in the solar system. This means that, on Venus, the Sun rises in the west and sets in the east, opposite to what we experience on Earth.

Venus was the first planet to be explored by a spacecraft – NASA’s Mariner 2 successfully flew by and scanned the cloud-covered world on December 14, 1962.

Figure 1: As it sped away in February 1974, NASA’s Mariner 10 spacecraft captured this view of Venus showing a world wrapped in a dense layer of toxic clouds. The clouds whip around the planet at about 100 metres per second), circling  the globe in about four and a half days. Credit: NASA/JPL-Caltech

Venus is still shining brilliantly in the western evening sky, and you certainly can’t miss it.  After eight months as the Evening Star, Venus is now rapidly heading back toward the Sun. and by the end of the moth it will be lost in the Sun’s glare as it nears inferior conjunction early in January.

Venus reaches its brightest on the 4th at -4.7 magnitude – known as greatest illuminated extent. It is defined as when the planet’s illuminated portion or day side covers the greatest amount of sky. At this time, we see Venus one-quarter illuminated, just like a 3- or 4-day old Moon. On the 7th the 4-day old waxing crescent Moon appear about 5° above the planet.

Mercury

Mercury returns to have western evening twilight this month and is best seen late in the month sharing the sky with Venus, Saturn and Jupiter. On the 27th the duo of Mercury and Venus will be parallel to the horizon and best viewed about 30 minutes after sunset. They appear at their closest on the 29th .

Figure 2:The planets after sunset on December 29th in the Western Sky

Earth

The Earth is at Solstice on the 22nd when the days are longest. On this day, the Sun is at its most southerly position with a declination of -23.5°.

Mars

Mars is now visible in the eastern dawn sky in the constellation of Libra during the first half of the month. It will then cross into the claw region of Scorpius and lastly into Ophiuchus. On the 3rd, the planet will be 4° to the south of the slender crescent of the waning 28-day old Moon – binoculars and a good eastern horizon will help you see it in the dawn sky.

Figure 3: The Moon and Mars in the early morning sky on December 3

Jupiter

Jupiter stands out in the western sky at the end of twilight, the only bright star nearby being 1st magnitude Fomalhaut in Piscis Austrinus. If you want to view the planet through a telescope, you should do so early in the month before it loses too much altitude. Jupiter’s brightest has decreased a little over half a magnitude since it’s opposition last August. Its equatorial diameter has also diminished by 32%. On the 9th, the 6-day old waxing crescent Moon will be 4° from the planet.

Saturn

Saturn is visible low in the western evening sky, setting around 10 pm mid-month. Although a little too low for meaningful telescopic observations of the planet, waxing crescent Moon provides a pleasant visual display at the end of twilight. First, on the 7th the Moon will be seen near Venus, then on the following evening near Saturn and finally on the 9th near Jupiter. With each visit the Moon appears within 5° of the planet.

Uranus

Uranus now past opposition, is in the northern evening sky at the end of astronomical twilight in Aries, transiting the meridian around 9 pm mid-month.

Neptune

Neptune comes to the end of five months in retrograde on the 2nd and appears high in the early north-western evening sky at the end of astronomical dusk.