These next two weeks, the three currently brightest planets draw steadily closer together. By Sunday, May 26, the trio — Venus, Jupiter and Mercury — will form its amazing, most compact gathering. On that night, your thumb held out at arm’s length might be able to cover the triple brightness of all three.

It’s true that we’ll have to look quite low in the sky not long after the sun goes down to see these planets.

But astronomical calculator Steve Albers judges this event will be the best of only three similar brightest-planet gatherings that will occur in the 21st century.

The brightest three meet. Venus is always the most brilliant of planets, with Jupiter almost always second-brightest. For a while, every few years, Mars kindles up to third-brightest or, occasionally, even second-brightest. But most of the time, Mercury is the third- brightest. The catch is that Mercury is so near the sun in space that only in certain prime weeks each year does it set long enough after the sun (or rise soon enough before the sun) for us to see properly. Fortunately, one of those prime periods for viewing Mercury is coming up.

Even so, I must admit that the naked-eye view of this great three-planet “conjunction” (meeting) will be challenging if the sky is a bit hazy. Binoculars will give the best view.

And although the field-of-view in binoculars is a lot narrower than that of the naked eye, the three planets will bunch so tightly they’ll fit together in almost any pair of binoculars on their closest nights.

To help explain what the planets will look like on different nights, we need to talk about what astronomers call “angular measure” in the sky. Your fist at arm’s length is about 10 degrees wide. Your thumb at arm’s length is about 2 or 2½ degrees wide.

The direction to look for these planets these next few weeks is west-northwest — basically where the sun went down. The best time will vary, but when these worlds form their tightest knot two weekends form now, the time when they appear brightest might be around 9 p.m.

At that time on Memorial Day weekend, the three planets will only be about 5 to 7 degrees above the horizon. So, you’ll have to have an unobstructed view down to quite low in the sky.

But let’s discuss this week’s sights first.

This week. Brilliant Venus is still low, more than a fist width to the lower right of Jupiter, which you should have no trouble spotting.

Mercury will be much lower this week, not likely visible until about Saturday. On that night, Jupiter and Venus will have pulled to within 10 degrees of each other and, if you can see all the way to the horizon, your binoculars might show you Mercury 5 degrees to Venus’ lower right.

The three planets will form an almost straight line about 15 degrees long.

Next week. The moon is rather near the star Spica on Tuesday, May 21, and not too far from Saturn on Wednesday, May 22.

By the next night, Thursday, May 23, Mercury has climbed to become directly to the right of Venus, and they are only 1½ degrees apart. Jupiter then is just 5 degrees upper left of Venus.

On Friday, May 24, Venus and much less bright Mercury are even a bit closer together, their closest in this encounter. Then come Saturday and Sunday: The three bright planets from a triangle whose longest side is about 3 degrees long on Saturday and less than 2 ½ degrees long Sunday.

Conjunction continued. The Memorial Day column will discuss the rest of the great planet gathering, including the nights when the two brightest planets — Venus and Jupiter — are at their thrilling closest together. For an animation of the whole gathering, see may2013planets.

A star-hiding for telescopes. If skies are clear around 9:55 p.m. Friday, May 24, telescopes in southern New Jersey should see the narrow dark edge of the near-full moon hide the double star Beta Scorpii.

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