Jupiter puts on a show for April’s night skies

What's up in the night sky over Oak Bay's Cattle Point

What’s Up for April 2016? Jupiter, Mars, the Lyrid meteor shower and 2016’s best views of Mercury.

Jupiter, where NASA’s Juno mission will begin orbiting on July 4, continues to shine almost as brightly this month as last.

And eagle-eyed telescope viewers will see a transit, a shadow transit, an occultation and an eclipse of Jupiter’s moons – all on one night: Wednesday and Thursday April 6 to 7. Io transits first, crossing the planet beginning at 18:52 p.m. PST. Its shadow can be seen less than an hour later.

Next, Jupiter occults, or eclipses, Europa as Europa slips behind the giant planet at 19:48 PST. At midnight, Europa reappears from its eclipse, dramatically leaving the shadow of Jupiter. Ganymede transits the planet beginning at 22:01 PST April 7.

Check out the other planets in April, too.

Mercury is always a challenging object to view, but this month you can spot it after sunset about 10 degrees above the horizon. Through a telescope you can see its phase. It will appear like a tiny crescent moon, with about 1/3 of its disk illuminated.

Mars is finally visible before midnight this month. It rises in the southeast over Mount Baker at about 10 p.m. by the end of April. The best observing of Mars will be when it is highest in the sky.

This means a few hours before dawn. Its brightness and apparent size increase dramatically this month. By month’s end Mars appears nearly twice as bright as at the beginning of the month.

About mid-month you’ll see Mars near its rival in the sky: the similar-coloured red supergiant star Antares. The name Antares means “equal to or rival of Mars.”

Earth moves almost twice as fast as Mars does, so it often passes Mars in their race around the sun. This causes “retrograde motion,” an illusion we see from our viewpoint on Earth.

Retrograde motion happens as Earth catches up to Mars, causing Mars to appear to slow its eastward motion against the stars.

After a few days, when Earth has overtaken Mars, Mars seems to move westward. Eventually, Earth moves far enough around its orbit that Mars appears to be moving eastward again.

April features one meteor shower, the Lyrids.

A meteor shower occurs annually for each comet that has left a significant trail/tail orbiting the Earth. We see these showers as the Earth passes through the relatively “still” comet tail. That is why the Lyrids “appear” every April. They are not “coming” at us. It is we (on Earth) who cross the tail once per year.

This year the Lyrids are marred by the full moon. The best time to view will be just before dawn on April 23, when the constellation Lyra is overhead and the moon will be near to setting. You recall that the planets walk the ecliptic from east to west just as the sun and moon do. Usually any bright objects on this arch are planets. But occasionally some bright object turns out to be a star, i.e. a galaxy or actual star.

This month Arcturus shines brightly over Mount Baker. Arcturus is the fourth brightest star in the night sky and is relatively close at only 36.7 ly (light-years) from Earth. Alpha Centauri is the closest star system to our Solar System at 4.37 ly. The average distance between stars in our galaxy is 4 ly.

An hour before sunrise looking south, you’ll see an upside down triangle of Saturn and Mars on the top base and Antares, a Star (super red giant), on the bottom. Antares is known as “the heart of the scorpion.”

Along with Aldebaran, Regulus and Fomalhaut, Antares comprises the group known as the “Royal stars of Persia.” It is one of the four brightest stars near the ecliptic.

For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.

See more at: http://skyandtelescope.com/observing/sky-at-a-glance/this-weeks-sky-at-a-glance-april-1-9/#sthash.wcKNkOVt.dpuf.

Find out about NASA’s Journey to Mars missions at mars.nasa.gov. Learn about all of NASA’s missions, including Juno, at nasa.gov and about JunoCam at missionjuno/swri.edu/junocam.

Meet the RASCals of Cattle Point at facebook.com/groups/VictoriaRASCals. The group meets at Fairfield Community Centre Mondays at 7:30 p.m.

Dark skies to all friends of Cattle Point Star Park.

Prepared by Bill Smith and the RASCals of Cattle Point. Summary from the transcript of “What’s Up in April 2016” by NASA announcer and astronomer Jane Houston Jones with specific permission for localization to Cattle Point Dark Sky Urban Star Park and the Oak Bay News.

 

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