A moon, a planet and a star form a fine isosceles triangle in the southwestern sky Tuesday evening, October 8. The astronomical significance is really limited to another opportunity to encourage people to "look up" and appreciate the night sky. That is always a good thing.
Find a place with a low view in that direction and look at about an hour after sunset. Planet Venus will stand out brilliantly against the glow of dusk. To the upper left will be the crescent Moon, its darkened portion faintly illuminated by the reflection of sunlight off the Earth. Look down to the lower left of the Moon for the bright red star Antares.
This star is the prominent "heart" of the constellation Scorpius the Scorpion, which stands out in the summer evening sky in the south. As the Earth glides around the Sun, the summer evening stars (speaking for the Northern Hemisphere) are gradually disappearing in the sunshine, as autumn's stars take their place in the evening dark.
Binoculars will help you enjoy the view and makes finding Antares much easier, in the twilight. The Moon and its "earth shine" are outstanding in binoculars. The sight of the crescent Moon near stars gives such a three-dimensional effect.
The stars and planets over our heads look like they are equally distant from us, as if pasted to the underside of a great bowl with us inside. That's how the ancients thought of the Universe. The isosceles triangle of Antares, the Moon and Venus we see on Oct. 8 is only from our perspective.
In actuality, Antares is over 619 light years away, or three and a half QUADRILLION miles. The Moon is only about 238,000 miles away and Venus is 26 million miles at its closest to the Earth. The three heavenly bodies are making an extremely long and narrow triangle in deep space.
An isosceles triangle is one with each side equal. Before and after Oct. 8, the planet, star and moon will still make a triangle, but will be of varying lengths and angles and the heavenly bodies move apart.
Triangles are practically unlimited in the night sky. Just connect any three stars that are not in a perfectly straight line and you have a triangle. There is a constellation known as Triangulum the Triangle.
Triangulum is visible on October evenings in the northeast, just below the constellation Andromeda. Forming a narrow triangle, the base is at left and the apex is at right. Under dark skies and with binoculars, search just above (west) of the apex star for the galaxy M33. It will appear as a small, faint fuzzy spot. This galaxy, at magnitude 5.8 is the brightest in the sky after the Andromeda Galaxy M31, in the constellation next door. The two galaxies are part of the "Local Group" of galaxies that counts the Milky Way in its neighborhood. M33 is suspected to be a satellite of M31.
Page 2 of 2 - There is also a constellation visible in the far southern sky known as Triangulum Australe (Southern Triangle).
First quarter Moon is on October 11.
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Keep looking up!