For Heaven’s Sake - What Planet Dominates the Night Sky?  Jupiter May!


For Heaven’s Sake - What Planet Dominates the Night Sky?  Jupiter May!

Mon, 01 May 2017

By Tim Bratton, Ph.D., (Retired Historian and Amateur Astronomer), Special to The Collegian 

May 2 (Tues.): First Quarter Moon occurs at 9:47 p.m. CDT, when it will be 49.6 degrees above the SW horizon, 90 degrees east of the Sun, 32 minutes of arc in apparent diameter, and 234,885 miles away.  It will be then 4.15 degrees to the lower right of blue-white Regulus (Alpha Leonis, mag. 1.35), the brightest star in Leo the Lion.  Regulus marks the bottom of the “Sickle” or reversed “Question Mark” in that constellation.  Watch the Moon creep toward Regulus as the evening progresses.

May 6 (Sat.): The Eta Aquarid meteor shower, which occurs between May 3 and May 10, should reach its maximum of 50 “shooting stars” per hour this morning.  Unfortunately the radiant (apparent point of origin) of this swarm does not rise very high as seen from Jamestown until early morning, and we have to wait until the Moon sets so that the glare from that body does not interfere.  At 4 a.m. the shower’s radiant will lie to the upper right of the blue-white star Eta Aquarii (mag. 4.03), which will have climbed 8 degrees above the eastern horizon.  This sun is located at the bottom of the Y‑shaped “Water Jar” asterism within Aquarius.  Derived from Halley’s Comet, which returned last in 1986, these meteors enter the Earth’s atmosphere at speeds up to 41 miles per second.  This shower has been known since A.D. 401, when it was recorded by Chinese astronomers.  Eta Aquarids are swift and bright, some exploding into fireballs; 40-60% will leave trains of glowing and ionized gas behind them.  Any suspected Eta Aquarids will appear to move rapidly up from the radiant.  This shower can be detected even during daylight hours by directional radio antennae, since the ionized trails of the meteors will reflect distant radio waves to receivers.  

May 7 (Sun.): At 11 p.m. the waxing gibbous Moon will be 38¼ degrees above the SSE-S skyline, 29.94 arc-minutes across, 83% lit, and 247,970 miles distant.  The bright cream-colored object just 3.3 degrees to its upper right is the planet Jupiter (magnitude –2.4), which now reigns as the dominant “evening star.”  Mighty Jove, which could contain all the other major planets of the solar system combined, will be then 42.95 arc-seconds in apparent span, 99.7% illuminated, 507,064,630 miles from the Sun, and 425,821,255 miles from Earth.  Using nothing more powerful than 7x50 binoculars, you can see that Jupiter displays a small disk; how many of its four largest moons can you spot lurking near the gas giant?  Ganymede should lie to the right of Jupiter, and (in order of apparent distance from the planet) Europa, Io, and Callisto to its left.  Galileo observed these moons with his primitive refracting telescope in 1609-10, and they are often called the “Galilean” satellites in his honor.  All four moons are large and bright enough that they would be visible to the naked eye were they not drowned out in Jupiter’s glare; indeed, Ganymede is larger than the planet Mercury!  Were Ganymede orbiting the Sun instead of Jupiter, it would qualify as a major planet in its own right.

May 10 (Wed.): Full Moon takes place at 4:42 p.m., when it will be 29¼ arc-minutes across, 251,530 miles distant, and 39.3 degrees below Jamestown’s ENE horizon.  The May Full Moon is nicknamed the “Planting” or “Milk” Moon.

May 12 (Fri.): The Moon attains apogee, its farthest distance from the Earth this month, at 2:51 p.m.  At that time Luna will be 252,337 miles away, 29.42 arc-minutes in apparent span, 96.52% sunlit, and almost 61 degrees beneath Jamestown’s northern horizon.

May 18 (Thurs.): Last Quarter Moon takes place at 7:33 p.m., when it will be 29.88 arc-minutes across, 60.19% sunlit, 244,905 miles distant, and nearly 58 degrees below our city’s northern horizon.

May 22 (Mon.): At 5:20 a.m., a half-hour before sunrise, the waning crescent Moon will be 9.06 degrees above the eastern horizon, 32.41 arc-seconds in span, 16.3% lighted, and 229,040 miles away.  The dazzling white object 5.05 degrees to its upper left is Venus (mag. –4.6); the second planet of our solar system will be then 28.02 arc-seconds across, 42½% illumined, 56,125,785 miles from Earth, and 67,616,055 miles from the Sun.  The thick Venusian cloud cover reflects 76% of the sunlight that reaches it back into space, which explains why it is the brightest morning “star” this May.

May 25 (Thurs.): New Moon occurs at 2:44 p.m., when Luna will be 55.56 degrees above the SSW-SW skyline.  As it will be passing then 5.47 degrees beneath the Sun, no kind of solar eclipse is possible this month.  The Moon also will reach perigee, its closest approach to Earth this month, at 8:21 p.m.  At that time it will be 221,958 miles distant, 6.06 degrees above the WNW horizon (and to the lower left of the setting Sun), merely 0.27% lit (a slender crescent too close to the star to be visible), and 33.96 arc-minutes in apparent span.

Congratulations to U.J.’s graduating seniors; may you become “stars” in the firmament of distinguished alumni!