Waxing Crescent Moon, Photo Credit: NASA Goddard
(NASA Goddard)
This Week’s Sky: October 2 to 7

Jupiter shines bright in the evening sky, while Saturn reaches east quadrature.

October 3

The waxing crescent Moon makes a vivid appearance 2 ½° east of a bright companion at dusk. That glowing celestial body nearby? It’s Jupiter, and the pair will be visible across Canada until mid-evening. Use binoculars to enhance your view. Through a telescope, the crescent Moon and Jupiter will look spectacular. Tonight is also the perfect chance to spot Earthshine on the Moon. The darkened area (outlining the entire Moon) is sunlight reflected off the Earth and bouncing off the Moon before it returns to your eye. If you were standing on the Moon tonight and looked up, you’d see a near-full, brilliant-blue, white-and-brown Earth.

October 5

By nightfall, the moon will sit 3 degrees east of Saturn. (Stellarium)

The first-quarter Moon occurs early afternoon (EDT). This is a perfect opportunity to observe the Moon with a telescope. The line dividing the lit versus the dark parts of the Moon (the “terminator”) is clearly visible. The Sun rising along the terminator at a low angle brings out great detail through a telescope.

By nightfall, the Moon will sit 3° east of Saturn. In fact, the Moon will actually pass in front of, or occult, Saturn for observers in southern South America. These two large planets are favourites for telescope viewing, and on this occasion, Saturn’s magnificent rings will be visible. The Moon and Saturn appear fairly close in the evening sky. Look for Saturn and Jupiter to appear even closer in 2020.

Early Next Week

Saturn reaches quadrature on October 7. (Stellarium)

October 7

Saturn reaches east quadrature. That is just a fancy way of saying that Saturn will be 90° east, or to the left of the Sun. This occurs every year when the Earth moves in its orbit to a point where Saturn, the Earth and the Sun are in a 90° alignment.

At some point during the year, all five outer planets reach east quadrature (90° east of the Sun) at various dates, depending on where they are in their orbits. At this point, the planet is due south at sunset and easily visible in the early evening. In approximately six months, as the Earth moves to the other side of its orbit, the planet will reach west quadrature (90° west of the Sun). At that point, the timing of the planet’s visibility flips, and they will appear due south at sunrise.

When one of the outer planets and the Sun lie in a straight line, with the Earth in the middle, the outer planet is said to be “at opposition.” The outer planet rises at sunset and is visible all night. A superior conjunction occurs when a planet forms a straight line joining the Earth and the Sun, but with the Sun positioned in the middle. In this alignment, the planet is not visible because the Sun is in the way.

On July 9, 2019, Saturn was at opposition, and visible each summer evening. On January 13, 2020, Saturn will be at superior conjunction and its visibility blocked by the Sun.

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