What's Up - April 2016

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

Hello and welcome. I'm Jane Houston Jones from NASA's Jet Propulsion Laboratory in Pasadena, California.

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: April 6-7. Io transits first, crossing the planet beginning at 9:52 p.m. EDT. Its shadow can be seen less than an hour later. Next Jupiter occults, or eclipses, Europa as Europa slips behind the giant planet at 10:48 p.m. EDT. At three a.m. Europa reappears from its eclipse, dramatically leaving the shadow of Jupiter. Ganymede transits the planet beginning at 1:01 EDT 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 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-colored 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. 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 can find out about NASA's #JourneytoMars missions at www.mars.nasa.gov and you can learn about all of NASA's missions, including Juno, at www.nasa.gov

That's all for this month. I'm Jane Houston Jones.