Venus at its morning best

Although bright planets avoid this month’s evening sky like the plague, the evening’s loss is the morning’s gain: All five naked-eye planets populate the predawn sky. The steep angle of the ecliptic — the apparent path of the Sun across our sky that the planets follow closely — to the eastern horizon before sunrise at this time of year strongly enhances their visibility.

Dazzling Venus dominates the scene. Although it dims slightly this month, fading from magnitude –4.7 to magnitude –4.4, it remains far and away the night sky’s brightest point of light. The planet moves eastward relative to the starry backdrop, crossing from Sagittarius into Capricornus on March 7. (It then edges into southern Aquarius on the 23rd before entering western Capricornus on the 27th.) Venus reaches greatest elongation on the 20th, when it lies 47° west of the Sun and stands nearly 30° high in the east as twilight starts to paint the sky.

The inner planet continues to move away from Earth, so a telescope shows its disk shrinking and its phase waxing. Venus’ apparent diameter dwindles from 32" to 22" while its phase grows from 38 percent to 55 percent lit this month.

Mars stays close to Venus and moves nearly in parallel to our sister world during March. The Red Planet’s easterly motion relative to the background stars carries it into

Capricornus a day before Venus makes that border crossing. At 1st magnitude, Mars glows less than 1 percent as bright as its neighbor. A telescope won’t show any detail on the ruddy world’s 5"-diameter disk.

Another pair of planets tangos to the lower right of Venus and Mars. Mercury and Saturn make an attractive couple in early March. Saturn lies 2.5° below Mercury on the 1st, but the two appear even closer on the 2nd and 3rd. The magnitude –0.1 innermost planet slides 0.7° south (lower left) of the magnitude 0.7 ringed world at 13h UT on the 2nd.

Saturn gains significant altitude during March, making it a fine telescopic target by month’s end. Even small instruments reveal the planet’s 16"-diameter disk and spectacular ring system, which spans 36" and tilts 14° to our line of sight. Also look for 8th-magnitude Titan, Saturn’s biggest moon and the second-largest satellite in the solar system.

As Saturn moves slowly eastward through Capricornus, hard-charging Venus and Mars soon catch up. The three form a spectacular trio during the month’s final week. But the best views come on the 28th and 29th, when the waning crescent Moon lies close.

While Saturn climbs higher, Mercury sinks toward the horizon. You’ll find it hard to spot the inner planet after March’s third week. Even before it disappears, the rocky world shows only a small gibbous disk when viewed through a telescope.

As Mercury descends into bright twilight, Jupiter draws away from the Sun. The two meet March 20, when Mercury slides 1.3° south of its companion. You might spot them if you scan just above the eastern horizon through binoculars a half-hour before sunrise. By month’s end, magnitude –2.0 Jupiter climbs significantly higher and should be easy to see, though it still will be too blurry to show much detail through a telescope.

The starry sky

The great ship Argo rides high in the March evening sky. This enormous former constellation boasts several conspicuous sights, including the sky’s second-brightest star, magnitude –0.6 Canopus, and the False Cross, which many viewers mistake for the true Southern Cross in Crux.

The 18th-century French astronomer Nicolas Louis de Lacaille broke up Argo into three smaller constellations: Carina the Keel, Puppis the Stern, and Vela the Sails. The stars in all three retained their original Greek letters from Argo, however, so you won’t find Alpha (α) Puppis or Alpha Velorum. Only Carina contains an Alpha star, Canopus.

Lacaille also introduced a fourth constellation, Pyxis the Compass, from stars close to the original Argo. Intriguingly, it has its own set of Greek letters.

Pyxis fell into disuse early in the 19th century before American astronomer Benjamin Gould resurrected it in 1879.

Pyxis’ three brightest stars — Alpha, Beta (β), and Gamma (γ) Pyxidis — form a straight line that lies on the edge of the Milky Way’s visible glow. Although the constellation is relatively obscure, with magnitude 3.7 Alpha being its brightest star, the Compass does hold a few objects worth exploring with a telescope.

One of these is a wide double perfect for small instruments. SAO 199924 holds stars of magnitudes 7.1 and 7.9 separated by an easy 14". If you don’t have a go-to mount, aim your telescope at Alpha Pyx and place it at the northern edge of the field. If you use a wide-field eyepiece, Earth’s rotation will carry the double into the field 20 minutes later. The double itself lies only 25' south of Alpha.

Also look for the 8thmagnitude open star cluster NGC 2818. It lies in barren southeastern Pyxis. Its main claim to fame is as host to the only known planetary nebula in an open cluster. A 20-centimeter instrument will deliver nice views of NGC 2818.

Near the opposite corner of Pyxis resides another deepsky treat: the nearly edge-on spiral galaxy NGC 2613. A 20-cm scope shows this 10thmagnitude galaxy well, but you’ll get a better view using averted vision.

HOW TO USE THIS MAP

This map portrays the sky as seen near 30° south latitude. Located inside the border are the cardinal directions and their intermediate points. To find stars, hold the map overhead and orient it so one of the labels matches the direction you’re facing. The stars above the map’s horizon now match what’s in the sky.

The all-sky map shows how the sky looks at:

10 P.M. March 1 9 P.M. March 15 8 P.M. March 31 Planets are shown at midmonth

MAP SYMBOLS

Open cluster Globular cluster Diffuse nebula Planetary nebula Galaxy

STAR MAGNITUDES

Sirius 0.0

1.0

2.0

3.0 4.0 5.0

STAR COLORS

A star’s color depends on its surface temperature.

The hottest stars shine blue

Slightly cooler stars appear white Intermediate stars (like the Sun) glow yellow Lower-temperature stars appear orange

The coolest stars glow red

Fainter stars can’t excite our eyes’ color receptors, so they appear white unless you use optical aid to gather more light

BEGINNERS: WATCH A VIDEO ABOUT HOW TO READ A STAR CHART AT www.Astronomy.com/starchart.