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Saturday, April 25, 2015

EarthSky Tonight—Oct 1, Venus and Mars close but hard to spot after sunset

Courtesy of EarthSky
A Clear Voice for Science

The planets Venus and Mars are in conjunction today (Friday, October 1). However, if you live at mid-northern latitudes, it will not be easy to spot these two worlds after sunset. You will probably need binoculars to spot them low in the sky and in the glow of twilight. Our sky chart shows the sky scene for about 30 to 40 minutes after sundown, shortly before Venus and Mars follow the sun beneath the horizon.

We draw in the ecliptic on tonight’s sky chart to help explain the term conjunction. On sky charts, the ecliptic represents the Earth’s orbital plane projected onto the stellar sphere. Because the Earth and other solar system planets orbit the sun on nearly the same plane, the planets are always found on or near the ecliptic.

Keep in mind that planets do not necessarily reside right on the ecliptic. In fact, they usually do not. As you can see on tonight’s chart, Mars sits almost exactly on the ecliptic, whereas Venus lies some 6.5 degrees south of it. When the line connecting the two planets makes a right angle to the ecliptic, the two bodies are said to be in conjunction in ecliptic longitude.

People in the southern hemisphere will have a much easier time seeing Venus and Mars on these October evenings, because the ecliptic intersects their horizon at a much steeper angle at sunset. At mid-southern latitudes, these planets set about 2.5 hours after the sun.

If you see only one planet at dusk, it will probably be Venus. Venus – the 3rd brightest celestial body after the sun and moon – shines over 100 times more brilliantly than Mars.

Written by Bruce McClure

Astronomy Picture of the Day from NASA/JPL

CHANDRA Photo Album

U.S. Naval Observator Astronomical Information center

Universe Today

StarDate Online

Sky and Telescope

National Geographic

Space Com

Simostronomy Blog

Amazing Space

The York County Astronomical Society

Scope City

James S McDonnell Planetarium

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