As April begins, the moon is just south of the equator and almost full. While it’s setting on the western edge of the sky dome before and during dawn, you can look for two planets rising together in the east. Two more are joining them. Not everyone gets a fair chance to see all of them. Southern hemisphere observers have it good. Mercury, Mars, Neptune, and Saturn are in that order from top to bottom from south of the equator. Saturn and Neptune rise too close to sunrise to be seen just yet though. The farther north you are, the more the planets are in that order right to left. But also, the harder any of them are to see because of being in the glow of the coming sunrise. North of around 45° north, you shouldn’t expect to see these planets this month. You’ll have to settle for knowing there’s a beautiful close grouping. For naked eye observers, this is a three-planet grouping. Neptune requires magnification.
On the 1st, Mars’s south pole is tilted most toward Earth. That’s worth seeing if you are in the right place and have a big enough telescope.
The moon’s full on the 2nd and passes by Spica on the 3rd. Also on the 3rd, Mercury gives its greatest showing at greatest elongation of 27.8° west of the sun. Those who can see it and Mars can see the messenger planet is pacing Mars as they go down along the constellations. On the 3rd, Mercury is in Aquarius and Mars has just entered Pisces. Mercury’s at aphelion on the 4th, 0.47 astronomical units from the sun.
Mercury continues to follow Mars downward (or left) while Neptune and Saturn come up from below (or toward them from the left). Some southern observers with clear horizons and binoculars may spot the ringed planet starting around the 5th. If you can’t find it one day, look again the next. Neptune will require more magnification and perhaps a wait of a few more mornings.
As the moon crosses the sky, it occults Antares for observers in Madagascar and in Southern Ocean areas south of the Indian Ocean on the 6th. The moon’s at apogee on the 7th at 404,936 kilometers. And it reaches southern lunistice, 28.3° south of the equator, on the 8th. The lunar disk will be entering Sagittarius then. On the 10th, the moon’s at last quarter on the other side of Sagittarius.
Around the 8th, Mercury seems to pick up the pace as it chases Mars. Neptune seems to be holding still below them as Saturn slowly sinking below it becomes more of a naked eye object to more observers. It’s becoming obvious to anyone who doesn’t already know, these planets will soon be tight.
Mars is as close as 0.3° from Neptune on the 13th. And then the planet line-up, top to bottom, becomes Mercury, Neptune, Mars, and Saturn. The moon goes north over the equator on the 15th as it drops in on the planet grouping. When the moon is new on the 17th, Mercury is passing Neptune at a separation of 1.3°. And so the line-up becomes Neptune on top, Mercury next, then Mars, and Saturn. The line-up spans about 5°, making a view of the whole thing unsuitable for a telescope. But if you look in binoculars, you have a good chance. You might also try astrophotography with an exposure of several seconds to catch more light to make Neptune show up. Remember, the more you zoom in, the less exposure time you can have before you get star trails.
By the time of the close grouping, observers in low northern latitudes can see the naked eye planets very close to the eastern horizon in the twilight. You may feel you need a scorecard to keep track of the planets and their close passes by each other. Saturn and Mars are 1.19° apart on the 19th. Saturn and Mercury are just 0.46° apart on the 20th. Then Mars and Mercury are as close as 1.65° apart later that day. The three are within 1.7° of each other on the 21st. Then they spread apart–Saturn, Mars, and Mercury from top to bottom.
The view of Mercury proves fleeting for those who could spot it from north of the equator. The messenger planet disappears into the sunrise by the end of the month.
In the evening sky, Venus shines brightly above the western horizon at dusk. Uranus is somewhat close to the Pleiades. Venus will climb the celestial dome to pass 0.75° from Uranus on the 24th. Jupiter is about in the middle of Gemini, heading eastward for a close pass by Wasat at the end of this month. The big planet and the star will be about 0.6° apart.
The moon, at perigee 361,647 kilometers from Earth on the 19th, appears just 4.6° from Venus in the sky that night. Northern observers can see the lunar disk pass in front of many of the Pleiades stars that night and by Uranus also. Northern lunistice is on the 21st at 28.2° north. The moon’s 3.5° from Jupiter on the 22nd and 3.1° from Pollux on the 23rd. First quarter moon is on the 24th.
The moon occults Regulus on the 26th for sky watchers from the eastern U.S., across the Caribbean, to Central America, and northern South America. The moon goes south of the equator on the 28th and passes by Spica again on the 30th.
The Lyrid meteor shower is expected to peak on the 22nd. The meteors come from dust left behind by Comet Thatcher, last at perihelion in 1861. It’s still outbound in an approximately 400-year orbit. This is mainly a northern hemisphere shower with up to 15 meteors per hour for a typical peak. The radiant rises in late evening, so the waxing crescent moon will set before it’s up.