April 2016 should be a great month for sky watching. Every year, April is the single best month to see nearly every key star and constellation in the Hawaiian night sky, literally from the North Star to the Southern Cross. In addition, most of the planets put in a really good appearance here in April 2016.
North Star to Southern Cross
“North Star to Southern Cross” is the name of a well-known sky guide by Will Kyselka, who was a planetarium lecturer at Bishop Museum in the 1960s into the 1980s. “North Star to Southern Cross” was the first astronomy reference book I bought when I started my planetarium career in Seattle, long before I came to work in the same planetarium theater as its author. The book is still in print, and is available at the Bishop Museum’s Shop Pacifica.
While Will’s book is an excellent guide to the night sky for anyone in, say, the continental U.S., its title refers to something that is specific to Hawaii among the 50 states: we are the only state where you can see the whole expanse of stars from the North Star to the Southern Cross. April is a good time for this, with the Big Dipper high overhead, the Little Dipper and the North Star visible as always, and the Southern Cross coming up in the evening sky.
The Museum’s April star map illustrates this. Like all of our monthly maps, this one is good for 10 p.m. on the first day of the month, 9 p.m. for the middle of the month, and for 8 p.m. at the end.
The North Star remains pretty much in place; the Little Dipper, which contains the North Star at the end of its handle, should be visible from a clear dark sky, as the dipper is no longer plunging straight at the horizon. The Big Dipper is high overhead.
You can use the handle of the Big Dipper to “arc to Arcturus,” the brilliant star in Bootes that is known as Hokulea in the islands. You can keep on going to “spike to Spica” in Virgo; and continue all the way to the Southern Cross, just rising in the east southeast at map time. The Southern Cross (officially called “Crux”) itself is very small and compact, and hugs the horizon; if you want to find it, find a flat southern horizon, such as looking over the ocean.
Here in April, the great winter constellations are also still visible. They are now low in the west at map time; the parade includes Orion, Canis Major, Auriga, and the Gemini. Meanwhile Leo the Lion, the classic spring constellation and the first of Hercules’ 12 labors, is in the center of our April sky. Below Leo is the second labor of Hercules, the snaky constellation on Hydra.
On this April map, Orion is just about the set in the west. Once he is gone (about three hours after map-time), his nemesis, Scorpius the Scorpion, will be fully visible in the east south east. As mentioned below, the planets Mars and Saturn appear near Scorpius in this April’s morning sky.
Planets in April
Jupiter is the only planet on our sky map for April, and the only planet visible throughout the month in the mid-evening. The planet is the brightest dot in the evening sky, several times brighter than even the brightest star. Throughout the month, it lies just below Leo the Lion.
In early April, look for Jupiter 1/3 of the way up in the east at dusk. Jupiter crosses the top of the sky at 11 p.m. in early April and sets in the west at 5 a.m. By the end of April, look for Jupiter 2/3rds of the way up in the east at dusk; it will be high in the south by 9 p.m., and sets in the west at 3 a.m.
Mars will be at its brightest in ten years this coming May; as it heads to this peak, you will see it increase dramatically in brightness in April.
Mars rises in the east at 11 p.m. in early April, amid the stars of Scorpius. Throughout the month, Mars will be just above Antares, the brightest star in the Scorpion. Mars will be in fact about six degrees above Antares in April, which is the width of three fingers held at arm’s length. Antares has a similar orange color to Mars, and its name means “Mars’ rival.” However, while the brightness of Antares will remain steady, at 1.03 magnitude, Mars above it will double in brightness in this single month. You can use Antares to observe the change in the red planet’s brightness. In early April, Mars shines at minus 0.5 magnitude, already somewhat brighter than Antares. By the end of April, Mars shines at minus 1.4 magnitude, which is almost exactly the same brightness as Sirius, the sky’s brightest star. By the end of the month it will be very obvious that Mars way outshines Antares, just below it.
Mars rises at 11 p.m. in early April, is halfway up in the south at 4 a.m., and is still partway up in the west by daybreak. By the end of the month Mar rises at 9 p.m., is due south at 2:30 a.m., and is 1/3 of the way up in the west at dawn.
As we continue into the next month, Mars will keep getting brighter, heading for its peak brightness in late May; by May 21, 2016, Mars will shine at minus 2.1 magnitude, nearly as bright as Jupiter, and the brightest Mars has been in a decade.
Saturn rises in east about 30 minutes after Mars; it rises at 11:30 p.m. in early April and 9:30 p.m. in late April. Saturn is just a little less than a palm’s width to the left of Antares all month; and all month, Mars blazes above both Antares and Saturn. In fact, Saturn, Antares and Mars make are nice triangle all month, with Mars on top. Saturn shines steadily at 0.3 magnitude all month, and its pale yellow-white makes a nice contrast to the orange blaze of both Antares and Mars.
All of April Venus rises in the east at 5:40 a.m. and is washed out by the dawn light a few minutes later. Minus 4 magnitude.
Mercury has its best evening appearance for 2016 this April. Look for it as early as April 5; if you look west at 7:15 p.m., Mercury shines at minus 1.16 in the dusk, about 5 degrees (three fingers) above the horizon. You will have 30 minutes to catch it before it sets at 7:45 p.m. By the 18th, Mercury will be a full ten degrees above the horizon at dusk (one palm’s diameter), setting at 8:15 p.m. After that, you’ll have only a few more days to catch Mercury; it will be lost in the dusk light by the 25th or so.
Mercury can be tricky to find, always huddling low near the horizon at dusk or at dawn. On April 8, the slender crescent moon can help. Look for the moon low in the west around 7:30 p.m. that night; Mercury is the bright dot to the moon’s lower right.
Other Sky Events in April
Lyrid Meteor Shower
Best Viewing Times: 12:01 a.m. to dawn on April 21 and on April 22
The year’s longest gap between major meteor showers is between the Quadrantids in early January and the Lyrids in late April. Unfortunately, that villain of good meteor-viewing, the full moon, will be a major interference with the Lyrid shower this year. The best viewing times for the Lyrids will be from 12:01 am to dawn early on April 21, and from 12:01 am to dawn early on April 22, Hawaii Standard Time. The shower is active from April 16-25. While not one of the strongest showers, the Lyrids can produce up to twenty meteors per hour. That said, on the prime viewing mornings of April 21 and 22, 2016, the moon is either full or near-full, making it the worst shower of the year in terms of moonlight. (Not only is the full moon bright, it’s up all night.) The Lyrids come from the debris of Comet C/1861 G Thatcher.
Moon Phases (Hawaiian Time Zone):
Third Quarter: March 11 & April 29
New: April 7
First Quarter: April 13
Full: April 21