A beautiful crescent Moon will be involved in a sort of planetary trifecta in the predawn sky beginning Monday, passing in the vicinity of bright planets on three consecutive mornings.

On Monday, Jan. 27 the Moon will visit Mars. On Tuesday it will pass near Venus and on Wednesday you can use the slender lunar sliver to point the way to Mercury. If your local weather cooperates it may be worth setting your alarm for about an hour before sunrise; then simply head out and take a look toward the southeast sky.

A morning-by-morning guide:

Look low toward the southeast sky this morning and youll see the crescent moon with a fairly bright yellow-orange "star" hovering above and to its left. This will be Mars. During January, Mars has been rising about 3 to 4 hours before the Sun.

Although relatively far, 169 million miles (271 million kilometers) from Earth on this morning, and shining at magnitude +1.4, Mars has been hardly boring. It moved from the constellation of Libra into Scorpius on the 20th, and quickly buzzed past the arc of three stars known as the "Crown of the Scorpion."

The slender sliver of the Moon now poses below and to the right of the dazzling planet Venus, unmistakably the brightest "star" in the sky. All during January Venus has drawn peoples eyes to the southeastern sky before and during dawn.

Venus rises within a half-hour of 4 a.m. local time all winter and spring as seen from mid-northern latitudes. Currently, this is nearly two hours before the first light of dawn.

Like the Moon, Venus goes through phases as seen from Earth. Venus arrived at its greatest western elongation from the Sun (47 degrees) on January 11, and in a telescope its disk achieved what astronomers call dichotomy the appearance of being exactly half lit just a few days later. If you train a small telescope on Venus now, youll see it as a small, featureless gibbous phase.

The Moon is noticeably slimmer and lower as compared to recent mornings. About 45 minutes before sunup youll find it roughly 10 degrees above the southeast horizon. Your fist held at arms length is roughly equivalent to 10 degrees, so the Moon should appear about "one fist" up from above the southeast horizon.

If you look a bit more than one fist over to the left of the Moon, youll almost certainly notice a very bright zero-magnitude object perhaps shining with a yellowish-orange tint. That's Mercury, the innermost planet of the solar system.

Sometimes called the elusive planet because it usually remains close to the Sun and hidden by solar glare, Mercury is also relatively easy to spot at times. This week is one of those occasions.

Mercury was barely visible in the evening sky after sunset on New Years Day. You probably would have needed binoculars to glimpse it at all. Mercury then passed through inferior conjunction a point in space right between the Sun and Earth on Jan. 11.

Since Jan. 18 Mercury has been rising just above the dawn horizon while getting progressively brighter. It is now at its best for viewing and won't get this good again until September. So rouse yourself out of bed some morning this week and take a look!