Venus has been known since prehistoric times. It is the brightest object in the sky except for the Sun and the Moon. Originally, it was popularly thought to be two separate bodies: Eosphorus as the morning star and Hesperus as the evening star, later scientists proclaimed that was inaccurate.

Venus is usually visible with the unaided eye. Sometimes  referred to as the “morning star” or the “evening star”, it is by far the brightest “star” in the sky. There are several websites dedicated to tracking the exact positions of all of the planets in the solar system, including Venus.

In order to find Venus in the night sky it is helpful to use a star map. To find a planet’s position at any chosen time we can find out the planets celestial coordinates and plot it. Celestial coordinates are to the sky what geographical coordinates are to the Earth.

Imagine extending the Earth’s axis infinitely into space, north and south. In the past people believed that there was a giant sphere to which the stars were attached–the celestial sphere. The Earth’s axis would pierce that sphere in two places: the celestial North Pole and the celestial South Pole. If you imagine the surface of the Earth being inflated like a giant balloon until it touched the celestial sphere, the Earth’s equator would be touching the celestial equator.

The “celestial latitude lines” represent celestial coordinate known as declination. Just as latitude on Earth increases from 0 to 90 degrees as you move from equator to Pole, declination in the sky increases from 0 to 90 degrees as you look progressively north from the celestial equator, and from 0 to -90 degrees as you look progressively south from the celestial equator.

Conversely, right ascension corresponds to longitude on Earth. Unlike longitude, which is measured in degrees and minutes, right ascension is measured in hours and minutes. There are 24 hours of right ascension corresponding to the full sweep of 360 degrees around the celestial equator. Simple division will tell you that each hour of right ascension must be equivalent to 15 degrees of arc.

Celestial coordinates specify which direction something is with respect to Earth, but not the distance to the object. For objects within the solar system (comets, planets, moons, asteroids), distance is often specified in Astronomical Units (AU)–an AU is the average distance from the Earth to the Sun = 149,597,870 kilometers (92,955,730 miles).  For objects outside the solar system, the light year (ly) is often used. This is the distance light travels in a year. One light year is equal to 63,240 AU.

Using right ascension, declination, and distance you can plot the celestial coordinates of Venus on a star map in order to locate it in the night sky.

On June 8, 2004, Venus passed directly between the Earth and the Sun, appearing as a large black dot travelling across the Sun’s disk. This event is known as a “transit of Venus” and is very rare: the last one was in 1882, the next one is in 2012 but after than you’ll have to wait until 2117. There is more known now about this transit, but early on in spawnd several trips to our sister planet, Venus.

The first spacecraft to visit Venus was Mariner 2 in 1962. It was subsequently visited by many others (more than 20 in all so far), including Pioneer Venus and the Soviet Venera 7 the first spacecraft to land on another planet, and Venera 9 which returned the first photographs of the surface. The first orbiter, the US spacecraft Magellan produced detailed maps of Venus’ surface using radar. ESA’s Venus Express is now in orbit with a large variety of instruments.

Venus photo in the public domain, credit: NASA

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