Jupiter and Sirius—until it departs—continue to dominate the evening sky in April. This year’s best evening appearance of Mercury in mid-April precedes its transit across the Sun on May 9. Meanwhile, Mars brightens on its way to next month’s closest approach since 2005. The Mars-Saturn-Antares triangle, prominent in morning, can also be seen rising very late in evening. Don’t miss this spring’s offerings to get close-up telescopic views of some planets!
First, some dates to keep in mind.
April 7: The new moon occurs at 4:24 a.m., and the moon at perigee at 11 a.m. Large tides!
April 8: The young crescent Moon, age 39 hours, is easy to see in twilight. Look for Mercury to the moon’s lower right.
April 10: The moon occults Aldebaran in daytime; look at it with a telescope. In the evening, find this star and the Hyades cluster closely to the lower right of the moon, a spectacular sight for binoculars!
April 12: Spica is at opposition, visible all night.
April 13: The moon is at first quarter, half-full in the afternoon and evening sky. Today and for a day or two before and after, install a single polarizing filter in your telescope’s low-power eyepiece, and rotate the eyepiece to darken the sky and improve the contrast of moon against the blue daytime sky.
April 16-23: Before dawn, Mars and Saturn reach their minimum distance apart, 7.2 degrees. Stopping short a few degrees north-northwest of Antares, Mars begins to retrograde on April 17. The red planet will move nearly 16 degrees west by June 29.
April 17: The moon is near bright Jupiter at dusk. On April 17 and 18, Mercury stands near greatest elongation, reaching its greatest altitude at dusk for 2016, but it begins to fade rapidly later this week.
April 20, 21: The moon is near Spica most of night. The full moon occurs on April 21 at 10:24 p.m.
April 24, 25: Four hours after sunset until dawn, view a spectacular gathering of the moon, Mars, Saturn and Antares.
In mid-April at dusk, Jupiter shines bright and steady well up in southeast, while next in brilliance, the blue-white “Dog Star” Sirius twinkles in the southwest. Catch Mercury before it reaches its high point low in the west-northwest April 17 and 18; it will still outshine golden Arcturus in the east-northeast to east This innermost planet of our solar system passes greatest elongation on those dates, when it appears farthest from the sun, 20 degrees this time around.
Mercury will get farther from the sun on other occasions this year, but this time, the planet is almost directly above the sun, which is 9 degrees below the horizon at the time of our evening chart/ This arrangement results in the best apparition of Mercury in the evening sky of this year. But don’t wait! As it circles the sun and comes around to the near side of its orbit, Mercury shows less of its sunlit side. Moreover, features large and small on its rough, rocky surface cast shadows, causing the planet to fade rapidly after greatest elongation. Mercury shines at magnitude -1 on April 7-8 and magnitude 0 on April 17, before fading to +1 on April 22-23, and +2 on April 27.
If proper equipment is used and precautions taken to avoid eye damage, you will be able to observe Mercury in silhouette against the disk of the Sun on Monday morning, May 9. More on this transit next month.
After Mercury fades away into the bright western twilight in late April, there are still several bright stars remaining in the western sky. Each evening within an hour after sunset, keep track of the stars Rigel, Aldebaran, Sirius, and Betelgeuse. By late in May, they’ll all be gone.
In April and early May, you can stay up late into the evening to view the pretty triangle of Mars-Saturn-Antares. On the night of April 24, four hours after sunset, see this triangle below and lower right of the waning gibbous moon, while Jupiter shines high in the southwest. On April 25, at the same late hour, you’ll find the moon low in the east-southeast, to the lower left of the triangle.
Jupiter, with its cloud belts and four bright moons discovered by Galileo, and Saturn, with its rings, are impressive showpieces for even small telescopes!
But Mars is usually not all that impressive, except within a couple of months of its oppositions, when you can get glimpses of surface features. At this year’s opposition, Mars is low in the sky, so it is best viewed when it is highest, as it passes due south. In mid-April, that happens around 3:30 a.m. Next month, we’ll have more on observing Mars, its surface features, rotation and seasonal changes.
As for events this month: The Whitewater Preserve will be hosting a star party on Saturday, April 2, from 7:30 to 10 p.m. Reservations required; call (760) 325-7222.
The Astronomical Society of the Desert will be hosting its popular monthly star party on Saturday, April 16, from 8-10 p.m., at the Visitor Center of the Santa Rosa and San Jacinto Mountains National Monument on Highway 74, within 4 miles south of Highway 111 in Palm Desert. Check the society’s website at www.astrorx.org for listings of our next lecture meeting—Dennis Mammana on “Capturing the Cosmos” (sky photography)—at 7 p.m. on Friday, April 8; and our next high altitude star parties at Sawmill Trailhead starting at dusk on April 2 and April 30. Check the separate link to our “Impromptu Star Parties,” which could be announced on short notice at any time.