Planet parade in the morning sky Understand article

Right now (and continuing until late February 2016), Mercury, Venus, Saturn, Mars, and Jupiter are visible in the sky in a straight line: a rare astronomical show.

Our solar system is essentially flat, with all the planets orbiting the Sun in a plane that is called the ecliptic. As a result, an observer on planet Earth who looks for the other planets in the night sky will always find them somewhere in a great circle: the zodiac.

Each planet has its particular orbital speed according to its distance from the Sun and Kepler’s third law, which describes where on the zodiac it can be found on a certain date. While the inner planets Mercury and Venus stay rather close to the Sun, which limits their night-time visibility to the time around sunrise and sunset, the other planets may be visible all night long. Thus at a given date and time, it may be possible to see several, one or even no planets at all.

Right now (and continuing until late February 2016), all the planets that are visible to the naked eye gather in the morning sky, like beads on a string. Closest to the Sun – and thus to the eastern horizon before sunrise – is Mercury, followed by the much brighter Venus. Further south, Saturn and Mars can be found, then Jupiter in the west.

During the next few days, the waning Moon will also make its way through the planet parade. It will set together with Jupiter on 28 January, will be close to Mars on 1 February near its last quarter, and will rise together with Mercury and Venus as a thin crescent on 6 February.

In late January to late February 2016, early risers have the opportunity
to see five planets in pre-dawn skies, with the naked eye.
Image courtesy of NASA / JPL-Caltech


The original article is available on the website of the Haus der Astronomie (in German).