The beautiful cool nights of April force you to choose which planet you want to observe in the early evening: Mars, which sets in the west, or Jupiter, which rises in the east. Unless your local horizon is obstructed in the west, we recommend you start with Mars.
The movement of Mars
2017 isn’t a big year for the red planet. Since it’s now very far from Earth, its apparent diameter is small and its surface details remain blurry through a telescope. During the next opposition of Mars, in July 2018, the situation will be very different. So why observe Mars now?
It’s with the naked eye that the red planet is now interesting. Its proximity to the Pleiades cluster and the star Aldebaran, both in the constellation Taurus, gives you a good chance to follow Mars easily as it moves among the stars. By gazing westward at twilight, you can spot Mars under the Pleiades and Aldebaran in early April and see the planet slowly rise between the two objects as the days go by.
Mars reaches the middle position in late April. You can easily see the configuration on the evening of the 28th when a thin crescent Moon lies to the left of the celestial trio.
The opposition of Jupiter
Jupiter is at opposition on April 7, kicking off an excellent period of visibility. The giant planet shines above the east-southeast horizon at twilight, a few degrees above Spica, the brightest star in the constellation Virgo. You can freely compare Spica’s bluish twinkle with Jupiter’s fixed yellowish glow.
The full Moon joins the pair on the evenings of April 9, 10 and 11. The grouping of these three heavenly bodies near the horizon will be impressive and an excellent time to take photos.
For the more patient among you, observation conditions are best in the middle of the night when the planet is highest in the sky. Through a telescope, Jupiter’s turbulent atmosphere reveals a series of light and dark parallel bands while its four Galilean moons change their configuration hourly. And when Jupiter culminates in the sky, a new planet, Saturn, turns up in the southeast.
Saturn and its rings
Saturn emerges above the southeastern horizon around 2 a.m. this month. Despite the excellent visibility of the rings, which are at maximum tilt this year, observation conditions for the planet are unfortunately poor.
Saturn is now in the constellation Sagittarius, a region of the sky that never rises much above the southern horizon in our latitude. Except in rare instances, image quality will suffer from air turbulence. The gibbous Moon accompanies Saturn early in the morning on April 16 and 17.
Venus, a comet and earthshine
Venus is visible above the eastern horizon in the first light of dawn this month, and a thin crescent Moon joins it on April 23. A periodic comet, 41P/Tuttle-Giacobini-Kresak, approaches Earth during the month, and though it rarely becomes visible to the naked eye, an outburst could suddenly make it noteworthy. The comet moves through the constellation Draco and is circumpolar and therefore observable all night. Get your binoculars out!
Earthshine is clearly visible only when the Moon is a thin crescent. This pale glow is caused by sunlight reflected off Earth and onto the unlit portion of our satellite. It’s during “full Earth,” as seen from the Moon, that earthshine is most intense (hence around the new Moon). The best conditions for observing this glow occur at twilight and early in the night on the days right after the new Moon (April 27 to 30) or at dawn a few days before the new Moon (April 21 to 23).