Star Points for April 2012 by Curtis Roelle Venus Burning Bright As it has done for the past couple months, dazzling Venus continues to dominate the western evening sky. Mars is still riding high as well and, as Jupiter slowly sinks ever lower in the west, Saturn enters the evening lineup well placed for viewing. Observing from a hill overlooking all buildings and trees during the first two weeks of this month, it is theoretically possible to view four major planets at once with the naked eye in the evening sky -- five if you count the Earth. Here is a quick tour that is good for the first half of April. During evening twilight around 8 p.m., the most brilliant star-like object in the western sky is Venus. Between it and the horizon is the fainter gas giant Jupiter. Orange-red Mars is high in the southeast. Once it gets a little darker out around 8:30 p.m. you could use Mars to help locate the star Regulus in Leo. Regulus, the ?heart of the lion,? is just to the upper right of Mars. While the Earth was catching up, Mars appeared to be moving backward in the sky toward Regulus in what is known as ?retrograde motion.? By mid-month Mars will be resuming its forward motion. Retrograde motion is a sort of optical illusion. Although Mars and Earth are traveling in the same circular direction around the sun, sometimes Mars can appear to move backwards. A similar illusion is experienced when you?re riding in a car that is passing another slower moving car. As you pass, the slower vehicle appears to be moving backward relative to your own car, although both are actually traveling forward. By 9 p.m. Saturn is about ten degrees above the western horizon. You may need to wait another hour for it to get higher, depending on your local obstructions. Saturn rises higher and near midnight is getting well placed for viewing through a telescope. Just about any telescope can reveal its delicate rings. You could use Saturn to find the star Spica in Virgo. Spica is the bright star to Saturn?s right. Your best chance of seeing all four planets in the sky together during mid-April is between 8:30 and 9 p.m. But now back to this month?s big story: Venus. Because Venus? orbit is located inside of the Earth?s orbit, Venus never strays too far from the sun in our sky. When in the morning sky, Venus will typically rise a little before the sun. Likewise, when in the evening sky, it sets shortly after the sun. However, currently Venus? angular distance from the sun ? that is, the distance separating it and the sun as seen in the sky ? is about as great as it ever gets. What this means is Venus lingers for a long time in the evening sky. For several hours after sunset you can look out a window and still see Venus sinking slowly in the northwest. One of the interesting things about Venus is that in a telescope Venus, like the moon, shows phases. At the end of March, Venus? phase had changed from gibbous to a half lit globe. During April, Venus? phase shrinks to a crescent and, by month?s end, only 28% of its disc will be illuminated. Venus orbits closer to the sun than does the Earth and hence, is also traveling more rapidly. As Venus catches up to Earth, we see less and less of its sunlit side and view it as a shrinking crescent. Also, as Venus draws nearer to the earth its apparent size increases. During the month of April the apparent diameter of Venus, as seen from Earth in a telescope, increases by over 50%! Venus presents an interesting target in April for readers with just about any size telescope. Can you detect the crescent phase of Venus? What is the lowest magnification at which the crescent is still visible in your telescope? As far as surface markings on Venus go, don?t expect to see any with your telescope. Venus is shrouded in thick clouds and its surface isn?t visible. NASA?s Magellan spacecraft did manage to map its surface through the clouds in the 1990s using synthetic aperture radar (SAR) technology. But all we see optically is the bright sunlit 100% cloudy atmosphere. If you don?t have a telescope, you could participate in one of the public April activities organized by the Westminster Astronomical Society. Go to WestminserAstro.org and check the calendar tab for details.