Celestial Navigator – May 2015

The night sky tonight and on any clear night offers an ever-changing display of fascinating objects you can see, from stars and constellations to bright planets, often the moon, and sometimes special events like meteor showers. Observing the night sky can be done with no special equipment, although a sky map can be very useful, and a good beginner telescope or binoculars will enhance some experiences and bring some otherwise invisible objects into view. You can also use astronomy accessories to make your observing easier. Below, find out what’s up in the night sky for the month of May.

Monday, May 18, 12:13 a.m. EDT New Moon

The moon is not visible on the date of New Moon because it is too close to the sun, but can be seen low in the east as a narrow crescent a morning or two before, just before sunrise. It is visible low in the west an evening or two after New Moon.

Monday, May 25, 1:19 p.m. EDT First Quarter Moon

The First Quarter Moon rises around 1 p.m. and sets around 2:15 a.m. It dominates the evening sky.

Thursday, May 17, evening twilight

This is the best evening apparition of Mercury this year for observers in the northern hemisphere. Use Venus to help you locate it. Mercury is most easily located by sweeping with binoculars, but once you’ve located it, you should be able to see it with your unaided eyes.

Wednesday, May 20, 8:06–8:35 p.m. EDT.  Double shadow transit on Jupiter

The shadows of Io and Ganymede will be on opposite limbs of Jupiter, while the moons Io and Callisto will be central on the disk.

jupiters moons

Friday, May 22, 10 p.m. EDT Saturn at opposition

Saturn will be in opposition to the sun. Note how most of Saturn’s moons are in the same plane as the rings, except for Iapetus, whose orbit is tilted 8.3 degrees. At opposition, Iapetus is close to maximum elongation towards the west, while Titan is close to maximum elongation towards the east.

Wednesday, May 27, 10:01 p.m.–12:18 a.m. EDT Double shadow transit on Jupiter

The shadow of Io chases the shadow of Ganymede across the face of Jupiter, catching up with it and passing it at 11:48 p.m. EDT. The Great Red Spot will also cross Jupiter’s disk during this period.

Planets

Mercury is well placed for northern hemisphere observers in the evening twilight sky for the first three weeks of May.

Venus shines high in the western sky after sunset.

Mars moves from Aries to Taurus on May 3, too close to the sun to be visible.

Jupiter is well placed in the evening sky all month.

Saturn is just north of Scorpius’ “claws.” At opposition on May 22, it is visible all night.

Uranus rises just before the sun in Pisces.

Neptune is in the eastern morning sky in the constellation Aquarius.

Skywatching Terms

  • Asterism: A noteworthy or striking pattern of stars within a larger constellation.
  • Degrees (measuring the sky): The sky is 360 degrees all the way around, which means roughly 180 degrees from horizon to horizon. It’s easy to measure distances between objects: Your fist on an outstretched arm covers about 10 degrees of sky.
  • Visual Magnitude: This is the astronomer’s scale for measuring the brightness of objects in the sky. The dimmest object visible in the night sky under perfectly dark conditions is about magnitude 6.5. Brighter stars are magnitude 2 or 1. The brightest objects get negative numbers. Venus can be as bright as magnitude minus 4.9. The full moon is minus 12.7 and the sun is minus 26.8.
  • Terminator: The boundary on the moon between sunlight and shadow.
  • Zenith: The point in the sky directly overhead.

Night Sky Observing Tips

  • Adjust to the dark: If you wish to observe faint objects, such as meteors or dim stars, give your eyes at least 15 minutes to adjust to the darkness.
  • Light Pollution: Even from a big city, one can see the moon, a handful of bright stars and sometimes the brightest planets. But to fully enjoy the heavens — especially a meteor shower, the constellations, or to see the amazing swath across the sky that represents our view toward the center of the Milky Way Galaxy — rural areas are best for night sky viewing. If you’re stuck in a city or suburban area, a building can be used to block ambient light (or moonlight) to help reveal fainter objects. If you’re in the suburbs, simply turning off outdoor lights can help.
  • Prepare for skywatching: If you plan to be out for more than a few minutes, and it’s not a warm summer evening, dress warmer than you think necessary. An hour of observing a winter meteor shower can chill you to the bone. A blanket or lounge chair will prove much more comfortable than standing or sitting in a chair and craning your neck to see overhead.
  • Daytime skywatching: When Venus is visible (that is, not in front of or behind the sun) it can often be spotted during the day. But you’ll need to know where to look. A sky map is helpful. When the sun has large sunspots, they can be seen without a telescope. However, it’s unsafe to look at the sun without protective eyewear. See our video

 

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