Mercury meets up with Jupiter (Saturn and the moon, too!) in the morning sky this week

If you're of a certain age, you might remember a comic strip called "Mutt and Jeff." Mutt was a tall guy while in contrast, Jeff was quite short. Ever since they were created back in 1907, any pair of individuals of different sizes came to be known as a "Mutt and Jeff".

You might then say that in our morning sky this week, we're going to have a celestial version of "Mutt and Jeff." If you look low in the east-southeast sky at around 5:45 a.m. local time, you'll see them: the biggest planet in our solar system passing unusually close to the smallest planet in the solar system. 

In this particular case, our planet version of "Mutt" is Jupiter, the fifth planet out from the sun and the largest of the eight that comprise our solar system. It is a gas giant which measures 88,846 miles (142,984 kilometers) in diameter and has a mass one-thousandth that of the sun. Yet, Jupiter is 2.5 times more massive than the seven other planets combined. 

As for our planet version for "Jeff," we have Mercury, not only the smallest, but the closest planet to the sun. Compared to Jupiter, Mercury is a piddling little nothing. A tiny, rocky world, 3,034 miles (4,880 km) in diameter, it's less than 30% the size of Jupiter. 

Related: Best night sky events of March 2021 (stargazing maps)

Acquiring appellations 

In mythology, Jupiter was the king of the gods. Yet, when the ancients ascribed names to the planets in the night sky, how could they have known that Jupiter was indeed the largest of the planets? Besides, Jupiter was not the brightest — that honor belonged to Venus. 

But Venus was only visible for a few hours prior to sunrise or after sunset, at most, and never appeared more than halfway up in the sky. And more often than not, Venus would be out of sight during the middle of the night. In contrast, Jupiter could appear in the sky at any hour of night and at times could appear to soar much higher in the sky compared to Venus. Except in unusual circumstances when Mars came very close to Earth (as was the case last fall), there is no other planet other than Venus that can outshine Jupiter. As such, the Jupiter moniker was bestowed upon the object that ancient stargazers believed was the king of the planets.

It is easy to see how the planet Mercury acquired its name. In mythology, Mercury was the fleet-footed messenger of the gods. And in the sky, the planet Mercury was by far the fastest of all the planets. Being so close to the sun, Mercury would appear to dash back and forth from one side of the sun to the other. 

And on Saturday (March 6), Mercury will reach its greatest elongation — its greatest angular distance — to the west of the sun in our sky. It is, in fact, about as far from the sun as it can get, 27 degrees away. (For reference, your clenched fist held at arm's length measures about 10 degrees wide.) But while this might sound like a favorable opportunity to get a glimpse of the so-called "elusive" planet, if you live north of the equator it actually is not. 

Low down in a bright sky

The problem is that at this particular time of the year, the ecliptic — an imaginary line in the sky that denotes the general path of the sun, moon and planets — lies quite low in the eastern sky at sunrise for those in the Northern Hemisphere. So even though Mercury is quite far from the sun, its location relative to the horizon keeps it rather low in the sky and rather deep in the dawn twilight. 

Meanwhile, Jupiter, which was in conjunction with the sun on Jan. 28, has been slowly trudging out of the brilliant glare of the sun and with each passing morning, it has gradually edged back into view in the morning twilight sky. 

And on Friday morning (March 5), Jupiter and Mercury — the big and the small — or the "Mutt and Jeff" of the solar system if you will — passed unusually close to each other. 

How close?

When Jupiter and Mercury were at their closest on Friday (March 5) at approximately 1 a.m. EST (0700 GMT), they were separated by only 19.4 arcminutes, or 0.32 degrees, according to the skywatching site In-The-Sky.org. For skywatchers in the U.S., the planets were not visible at that time; in New York City, for example, Mercury and Jupiter rose at 5:19 a.m. and 5:20 a.m. local time, respectively. Considering that the average width of the moon measures 30 arc minutes or, one-half degree, means that on Friday morning Jupiter and Mercury were closer together than the apparent width of the moon. 

Such close approaches between these two planets do not happen very often. In the past 50 years, there have been only six such cases, the last happening in 2006 and the next not until June 2024. 

When the planets rise again this Saturday (March 6), they will be just over one degree apart. While Mercury has risen just before Jupiter for the last few days, Jupiter will take the lead on Saturday, rising in New York at 5:17 a.m. local time, two minutes before Mercury. The sun will rise about one hour later, at 6:22 a.m. local time in New York. 

When and where to look

To see this "dynamic duo" on Saturday (March 6), we recommend finding a "flat" horizon; a place where there are no tall obstructions, such as trees or buildings, in the direction toward the east-southeast. At 5:45 a.m., the two planets will be only about 5 degrees above the horizon (so the two planets will be only about "half-a-fist" above the horizon.) 

Jupiter, at magnitude -2, will be the brighter of the two, outshining zero-magnitude Mercury by more than six times. (Magnitude is a measure of brightness used by astronomers, with negative numbers denoting brighter objects.) Mercury will appear to the lower left of Jupiter. Your chances of getting a view of them will be enhanced if you use binoculars and scan the sky low in the east-southeast. Remember, the twilight sky will be quite bright, as the sun will be coming up only about an hour later.

There have been some reports from skywatching publications that Mercury and Jupiter will appear as if they had merged into a single star, but that is not true. You should easily be able to separate the two planets, both with your eyes and even more so with binoculars.

Room for two more

After this weekend, Mercury will rapidly scoot away from Jupiter to the east, but there is still one more event to watch for and that will happen five days later, on the morning of Wednesday, March 10. On that day, again around 5:45 a.m., low in the east-southeast, look for Mercury nearest to the horizon, Jupiter well to its upper right and about 10 degrees ("one fist") to the upper right of Jupiter will be a third planet: Saturn. 

Of course, Jupiter and Saturn received a lot of attention just prior to Christmas when they engaged in a spectacular get-together of their own, referred to as the "Great Conjunction." 

And addition to the three planets, we can add a fourth celestial interloper: a lovely, thin waning crescent moon that will hang about five degrees to the lower right of Jupiter. The sliver of the moon will be only 9% illuminated and a little over two days from its new phase. Again, binoculars will be beneficial when capturing a view of this "celestial summit meeting."

Don't forget that what you'll be seeing in the sky is all a matter of perspective. The moon will be about 239,700 miles (385,600 km) away. But Mercury is currently about 89 million miles (140 million km) from Earth, Jupiter 551 million miles (887 million km) away, and Saturn is nearly a billion miles (1.6 billion km) away from us, according to the skywatching site TheSkyLive.com.

But on this morning, you'll be able to sight all four in a single glance. Good luck and clear skies!

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications. Follow us on Twitter @Spacedotcom and on Facebook.