This is the Dudley Observatory Skywatch Line for Wednesday, August 10th and Thursday, August 11th written by Louis Suarato
One of the more frequently asked questions heard at star parties when guests are looking at a celestial object is “How far away is that?”. Many times, amateur astronomers don’t have the information readily available. So, here are the distances of many of the more common observing targets. Let’s start with the planets. A German astronomer by the name of Johann Daniel Titius proposed a law of planetary distances, where a formula could predict the existence of not only planets, but asteroids, and dwarf planets as well. This formula was popularized by another astronomer, Johan Bode, and is more widely known as Bode’sLaw. Bode’s Law states that the distances of planets follow a mathematical sequence. The formula assigns a number from 1 to 9 for each planet extending out from the Sun. Mercury is 1, Pluto is 9. A scaling factor is used beginning at 0 for Mercury, 3 for Venus, then doubled for each additional planet (6 for Earth, 12, for Mars, 24 for the asteroid belt between Earth and Mars, 48 for Jupiter, 96 for Saturn, 192 for Uranus, 394 for Neptune,and 768 for Pluto. To calculate the distance of each planet from the Sun in astronomical units (1 AU = 93 million miles), add 4 to each factor and divide by 10. So Jupiter’s distance would be calculated by (48 + 4)/10, or 5.2 astronomical units. Jupiter’s average distance from the Sun is actually 5.203 astronomical units, or 483.6 million miles. To find each planet’s distance from Earth, subtract that planet’s distance from the Sun in astronomical units from Earth’s distance from the Sun, or 1 AU. The distances for each planet are: Mercury – .613 AU (57 million miles); Venus – .277 AU (25.7 million miles); Mars – .524 AU (48.7 million miles); Jupiter – 4.203 (390.8 million miles); Saturn – 8.539 AU (794.1 million miles); Uranus – 18.18 AU (1.69 billion miles). The Bode’s Law correlation diminishes greatly for Neptune and Pluto. Neptune is 2.7 billion miles from Earth, and Pluto is 3.582 million miles away. The distances of the stars comprising the Summer Triangle are: Vega – 25 light-years (1 light-year = 5.8 trillion miles), Deneb – 1,500 light-years, Altair – 16 light-years. The brightest star in our sky is Sirius. Sirius is 8.6 light-years away. Bright Arcturus is 34 light-years distant. The closest galaxy to our Milky Way is Andromeda. The Andromeda Galaxy is 2.3 million light-years away.
The First Quarter Moon occurs at 2:21 p.m. Wednesday. The Moon sets 12:47 a.m. Friday, leaving the skies dark for your Perseid Meteor Shower viewing! Clear skies!