Observing Project 7A Charting the Movements of Venus

This is a non-telescopic project that can keep you busy for many years. It simply involves charting the position of Venus in the evening sky over the course of several apparitions. Here we will see two things. First, how the path of Venus in the sky and favorability of a given apparition will vary based upon the angle the ecliptic makes with the morning or evening horizon depending upon time of year. The other will show you over a period of ten years or so how apparitions repeat themselves over and over again in a regular cycle. During favorable apparitions, the time of greatest elongation occurs in late March when the ecliptic stands nearly vertical over the setting Sun, so Venus stands nearly 40 degrees above the horizon at sunset. Conversely at the unfavorable 1997 and 2005 apparitions the time of greatest elongation is in November when the ecliptic is flat relative to the horizon and thus the planet never at any time climbs more than 20 degrees above the horizon and sets just after twilight ends. The viewing in March 1996 and 2004 is further enhanced by the fact that Venus is about as far north of the ecliptic as is possible, giving the planet a bit of extra altitude. At the 1997 and 2005 elongations the planet is situated as far south in the sky as it can ever get so it lies even closer to the horizon than the angle of the ecliptic would suggest.

In addition to its movements, you can also try your hand at judging Venus' changing brightness. Venus will change in brightness over the course of an apparition from a minimum of about -3.3 to a maximum of about -4.7 before fading to just below magnitude -4.0 just before it disappears into the solar glare. This is something that will prove extremely challenging because there is so little to compare Venus to that is comparable in brightness. Jupiter can come within two magnitudes when it is at opposition, but when Venus goes past it each year Jupiter is near its minimum brightness. It may not be a great yardstick but it is as close to one as you are going to find.

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