April 6 – 19, 2015
Star light, star bright,
First star I see tonight,
I wish I may, I wish I might,
Have this wish I wish tonight.
Nursery Rhyme
Mt. Washington — The most luminous celestial objects next to the sun and moon greet us as day fades into night in the coming weeks. On the magnitude scale for heavenly bodies, the smallest numbers represent the brightest objects. A lower case “m” is the abbreviation for apparent magnitude. Consider the sun’s negative number, -26.90 m, in contrast to the positive number given to the dimmest stars visible with the naked eye, 6 m. The sun is so bright that it will injure our eyes if looked at directly. Looking directly at a full moon, -12.64 m, is refreshing to the eyes. The next brightest object visible from Earth is Venus, currently -4.04 m. The planet surprises the viewer when it appears, the first celestial light soon after sunset while the sky is still quite light. Venus is the wishing star of many a child’s evenings, visible in both country and city skies.
Although known as the Evening Star, Venus does not generate its own light, rather, like all planets and the moon, Venus reflects the light of the sun. Venus’ brilliance in Earth’s skies is owed to its yellow-white clouds of sulfuric acid droplets that are particularly reflective and to the planet’s proximity to the sun and to Earth. Venus is the second planet from the sun, after Mercury, and it is our closest neighbor in the solar system. To find the Evening Star, begin to gaze about 30° above the western horizon 10 minutes after sunset. Sunset is at 7:23 on the 6th and a minute or two later every day.
Jupiter, currently -2.28 m, is the next most luminous object visible from Earth and second to appear, about 10 minutes after Venus. Look up high and to the south. Jupiter, the largest planet in our solar system, is fifth from the sun. Its upper atmosphere consists of hydrogen and swirling clouds of ammonia crystals and methane. Only its distance from the sun and from Earth place Jupiter second in brilliance to Venus in our skies.
The fourth brightest object visible in the night sky is the brightest of all the true stars, that is, the brightest of the sky full of distant suns we call stars. Sirius the Dog Star, -1.47 m, is one of the closest stars to our solar system. Within half an hour of sunset, Sirius appears in the southwest, below Jupiter and to the left of Venus, completing a stunning triangle that stretches across the sky from south to west. All of this happens before twilight, around 8 p.m.!
The triangle shaped by Venus, Sirius and Jupiter continues to attract our gaze as the beautiful patterns of the winter constellations appear within it, visible until about 10 p.m.
Recommended:
Friday, April 10th, 8 p.m. Amherst Area Amateur Astronomy Association (5A’s) meeting. Guest speaker Dava Sobel, renowned former New York Times science reporter and author of The Planets, Longitude and Latitude, and Galileo’s Daughter. Amherst College Planetarium located at Morgan Hall. https://www.amherstastronomy.org/ and https://davasobel.com/?page_id=547
Global Astronomy Month, April 2015 https://www.astronomerswithoutborders.org
