Skywatchers are in for a cosmic treat this month: a rare alignment of four planets in the predawn sky.
Beginning around Sunday morning, stargazers will be able to see Mars, Venus, Jupiter and Saturn appear in a straight line across the southeastern sky before sunrise. The midmonth alignment is a relatively unusual opportunity for people to see multiple planets in the sky with the naked eye — and it's a prelude to an even rarer planetary alignment that will happen this summer.
To see the planetary quartet, skywatchers in the Northern Hemisphere should head outside about an hour before the sun comes up and gaze southeast, in the direction of the sunrise.
Looking east at a flat horizon, Jupiter, Venus, Mars and Saturn will appear "strung out in a line across the morning sky," according to NASA. If conditions are clear, all four planets will be bright enough to see with the naked eye, without the aid of binoculars or telescopes.
The same alignment is viewable before sunrise in the Southern Hemisphere. There, the sun's path in the sky is at a steeper angle to the horizon, compared to in the Northern Hemisphere, which means the string of planets will unfurl higher above the sunrise point.
In both cases, Jupiter will be the second-brightest planet in the celestial gathering but will appear lowest on the horizon, which could make it tricky to spot. That will change as the month goes on, according to NASA.
"Heading into the last week of April, Jupiter will be high enough above the horizon in the hour before sunrise to make it more easily observed," the space agency said in its monthly roundup of skywatching tips.
Though this month's skywatching event makes it look like the planets form a neat line in space, it's actually just a matter of perspective. Each planet in the solar system circles the sun on the same flat plane, which means that as they occasionally swing past each other in their orbits, they appear to form a straight line in Earth's skies. This tidy positioning, however, would look very different from any other vantage point in space.
The planets will be viewable in the predawn sky all month, and April's alignment will set the stage for an even more spectacular skywatching event this summer.
From late June to early July, five planets — Mercury, Venus, Mars, Jupiter and Saturn — will be visible in the sky before sunrise in a major alignment that only occurs every few years.