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Mercury will pass superior conjunction with the Sun on April 2 and then enter the western post-sunset sky, but it will be mid-month before the speedy planet swings far enough from the Sun to become easily visible. Once it appears, Mercury will have its best appearance of 2022 for observers in the Northern Hemisphere, but its poorest showing in the Southern Hemisphere. On April 28, Mercury will reach greatest eastern elongation and peak visibility at an angle of 21 degrees from the Sun. That same evening, the planet will shine in a dark sky only 1.4 degrees south of the Pleiades star cluster in Taurus. It will remain near the Pleiades on April 29 and 30, allowing views of the planet with the cluster in widefield eyepieces for several evenings. During April, Mercury will steadily diminish in brightness; starting the month at magnitude -1.78 and ending April shining at magnitude 0.42. Telescope views in April will show an apparent disk diameter that swells from 6 to 8.25 arcseconds. Its illuminated phase will decrease from nearly fully illuminated to a 33%-lit crescent on April 30. On April 17, Mercury will pass only 2 degrees to the north of Uranus, but their low altitude in a twilit sky will make seeing magnitude 5.9 Uranus a challenge.
Venus will continue to dominate the southeastern pre-dawn sky during April. As the month begins, the magnitude -4.4 planet will shine among the stars of Capricornus, forming a short line with far less bright Saturn and Mars. But Venus’ sunward swing will carry it farther east from those planets every morning. On April 4, Venus will pass into Aquarius where, on April 27 in the Americas, it will shine only half a degree from 69,000 times fainter Neptune. For observers around southeastern China, the two planets will approach to within one arcminute, but their vast difference in brightness will make it extremely difficult to see them together in a telescope’s eyepiece. The old crescent Moon will shine 5 degrees below (or celestial south of) Venus on the same morning. Venus will cross into Pisces on April 28. Two mornings later, on April 30, Venus will shine just 30 arcminutes to the southwest of six times fainter Jupiter, allowing both planets to share the view in a backyard telescope. Venus will decrease slightly in brightness during April, from magnitude -4.39 to -4.13, its illuminated phase will be slightly gibbous, and its apparent disk diameter will shrink markedly, from 21.6 to 16.78 arcseconds.
Mars will appear in the southeastern pre-dawn sky with several bright planets during April. It will commence the month in Capricornus, on the western end of a short line formed with Venus and Saturn. The rapid eastward motion of Mars will allow it to pass half a degree to the south of slower-moving Saturn on April 4 and 5, close enough for those two planets to appear together in the eyepiece of a backyard telescope. Mars and Saturn will shine with similar brightness, magnitude 1.04 and 0.86, respectively, but they’ll exhibit distinctly different colouration. On April 12, Mars will pass into Aquarius. The waning crescent Moon will shine a palm’s width below (or 6 degrees south of) Mars on April 26. That Moon, plus the lengthy string of bright planets Jupiter, Venus, Mars and Saturn, will make a splendid photo opportunity over several mornings. Over the month, Mars will increase slightly in brightness, from magnitude 1.07 to 0.88, while its 90-per-cent illuminated disk will increase slightly in apparent size in telescopes, from 5.19 to 5.74 arcseconds.
In eastern Aquarius and only 20 degrees west of the Sun, Jupiter will begin April shining very low in the eastern sky before sunrise. The tilted morning ecliptic will prevent the magnitude -2.0 planet from becoming observable at mid-northern latitudes until after mid-April. Observers in the tropics and in the Southern Hemisphere will have little trouble spotting Jupiter shining well above the eastern horizon before sunrise all month long. On April 12, faster moving Jupiter will pass less than 7 arcminutes to the north of Neptune, but their 10,000 times difference in brightness, their low altitude, and the surrounding twilit sky will make observations of their conjunction extremely difficult. On April 14, Jupiter will enter Pisces. Around that time, it will have stretched far enough west of the Sun to anchor a lengthy line of naked-eye bright planets that ends at Saturn some 30 degrees to Jupiter’s upper right (celestial west). Throughout April, bright Venus will move toward Jupiter. They’ll finally meet in a dark, pre-dawn sky on April 30, separated by only half a degree, with six times brighter Venus shining on Jupiter’s right (celestial west). The waning crescent Moon’s picturesque trip past the morning planets will carry it a few degrees below (south of) Jupiter and Venus on April 27. Although Jupiter will sit rather low in the sky for clear telescopic views during April, the planet will display a disk 35 arcseconds wide, crossed occasionally by the shadows of its four Galilean moons.
During April, Saturn will share the southeastern pre-dawn sky with Mars, Venus and Jupiter. It will begin the month positioned between reddish Mars and much brighter Venus while shining at magnitude 0.86. On the subsequent mornings, Venus will shift rapidly eastward away from Saturn, while faster-moving Mars will approach from the west. Mars will pass half a degree to the south of Saturn on April 4 and 5, close enough for those two planets to share the view in the eyepiece of a backyard telescope. Reddish Mars and yellowish Saturn will shine with similar brightness values of magnitude 1.04 and 0.86, respectively. While Saturn will remain ensconced in eastern Capricornus all month long, the period after mid-month will find the other bright planets stretching eastward to form a lengthy chain, each link spanning about 10 degrees. Starting near Saturn on April 24, and lasting until April 27, the pretty, waning crescent Moon will cruise past the planets, but five degrees to their south. Viewed in a telescope during April, Saturn will be 16 arcseconds wide, adorned with its ring system 37 arcseconds wide and surrounded by a number of brighter moons. With the planet’s tilt diminishing until 2025, a good deal of Saturn’s southern hemisphere will extend below its ring plane this year.
During the early part of April, blue-green Uranus will be visible low in the western sky for a short time after dusk, shining at magnitude 5.85 among the stars of southern Aries. Each subsequent night will see it descend into the post-sunset twilight. On April 3, the young crescent Moon will shine several degrees above (east of) Uranus. Hours earlier, observers in the Côte d’Ivoire region of Africa can see the Moon occult Uranus around 19:30 UTC, the third of 15 consecutive monthly lunar occultations of the seventh planet. On April 17, much brighter Mercury will pass to the right of Uranus (or 2 degrees to the celestial north), but Uranus’ low altitude and low brightness will make observing the conjunction a challenge.
Magnitude 7.9 Neptune will be parked on the border between Aquarius and Pisces in the southeastern pre-dawn sky during April. The planet will be slowly shifting away from the Sun, but the shallow angle of the ecliptic will keep it too close to the horizon for telescope observing until the closing days of the month. The faster eastward motion of Jupiter will carry it closely past Neptune on April 11-13. At minimum, the pair will be less than 10 arcminutes apart, but Jupiter will shine 10,000 times brighter than Neptune. Observers at tropical latitudes, where the pair will sit higher, in a darker sky, can attempt to view the challenging conjunction. On April 27 in the Americas, 69,000 times brighter Venus will shine only half a degree from Neptune. For observers in southeastern China, the two planets will approach to within 1 arcminute of one another, but that extreme difference in brightness will make a simultaneous observation of the two planets in a telescope eyepiece extremely difficult.
Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the Universe together.