Saturday June 9th two of the outer planets, Mars and Saturn, will be at the same heliocentric longitude of about 278o, and would be in what is called a heliocentric conjunction. Heliocentric (Sun-centered) coordinates uses an overhead view of the solar system with planet location given as degrees of heliocentric longitude. The heliocentric longitude is based on a view from the Sun and is given as the angle between a planet and the vernal equinox. The vernal equinox, 0o, is located within the constellation of Pisces the Fishes, and is the intersection between the ecliptic and the celestial equator.
As the Earth revolves around the Sun it ‘gives’ the Sun its apparent motion eastward along the ecliptic. When the Sun crosses the celestial equator at this intersection it is moving north. At the crossing northern hemisphere winter becomes spring – the opposite seasonal change for the southern hemisphere.
Despite having the same heliocentric longitude, when viewed from the surface of the Earth, the two show an east to west difference of about 2 hours of right ascension.
Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.
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And Uranus is at eastern quadrature. So what does that mean?
Mars opposes Neptune in the sense that each planet is 180 degrees from the other and using their heliocentric coordinates Mars is at approximately 155o while Neptune is at approximately 334o. This is called heliocentric opposition as the two planets are on opposite sides of the Sun. When two planets are in heliocentric opposition and separetd by 180o one planet will be in the morning skies, Mars, while the other is in the evening skies, Neptune.
The outer planet Uranus is at eastern quadrature today meaning that using the Earth, Sun, and Uranus the three form a right angle with Uranus 90o from the Earth and Sun. This places Uranus on the eastern side of the Earth as the Earth rotates. Whenever an outer planet is at or near eastern quadrature that planet or planets is to the east of the Sun and this places them in the evening or night skies.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.