July 2011

Saturn Amazes First Time Stargazers

The longest days, or shortest nights, occur around the summer solstice in June. Even in July stargazers still must wait later in the evening for darkness to fall in order to see the stars and planets. To observe objects like star clusters, galaxies and nebulae the sky is not sufficiently dark until around midnight. These types of objects require a dark sky and are known as “deep sky objects” due to their faintness.

One of my favourite deep sky objects is a star cluster in the constellation of Hercules. Locate the asterism of the Summer Triangle well up in the southeastern night sky. The three stars Altair, Deneb and Vega form the corners of the triangle. Vega, in the constellation Lyra, is the brightest of the three. Hercules is the constellation of stars to the right (west) of Lyra. A basic star map will help you find the Summer Triangle as well as Hercules easily.

Once you have located Hercules you will notice a group of four stars called “The Keystone” in the shape of a square slightly wider at the top than the bottom. A set of binoculars will reveal a fuzzy patch about one third of the way from the top star to the bottom star on the right (west) side of the Keystone.

This object is the finest globular star cluster in the northern skies. It consists of several hundred thousand stars lying at a distance of 25,100 light years. It is barely visible to the unaided eye under a very clear and dark night. A small telescope will start to resolve many of the stars in this cluster. In a larger telescope this star cluster is magnificent! It reminds me of diamonds scattered on a black velvet cloth.

Saturn appears about a third of the way above the southwestern horizon toward the zenith (overhead) an hour after sunset. Located in the constellation Virgo the golden coloured planet lies about 15 degrees (one and a half fist-widths at arm’s length) to the right of the blue-white star Spica. The Ringed Planet lies much closer to the star Gamma Virginis (Porrima) the second brightest in Virgo. At the beginning of July Saturn is a mere one-half degree (width of moon in the night sky) from this star. Stargazers watching Saturn will notice that the planet will move towards a point two degrees eastward (left) of Porrima by the end of the month. Viewing Saturn in a telescope is always exciting. Saturn reaches quadrature in July. This means that the shadow cast by the planet falls as far east as possible hiding a noticeable section of the far side of the rings from our view. This gives a three dimensional effect to the image. Observers who have seen Saturn for the first time are totally amazed that they can actually see the rings and moons of the planet. Participants at the Relay for Life (fundraiser for Cancer Research) held at the Fort William Historical Park stopped by our display to look through our telescopes at the Moon and Saturn. Comments included expressions such as “Unbelievable!”, “WOW!”, “You can really see the rings!”, “Do you have a picture hidden in the telescope?” and “Is that real!”. I have been observing the planets for nearly 50 years and each time I point a telescope at Saturn it is like that “first time” again. Our solar system is amazing, you just have to understand it and know where to look to find the planets, moons, comets, etc.

Kepler’s first law of planetary motion states that a planet revolves around the sun in an elliptical orbit. This means that there is a time of the year (January) when the Earth is closer to the sun and at another when we are farthest (July). On July 4 the Earth will be at aphelion (farthest from the sun). The Earth is at a greater distance from the sun in the summer in the northern hemisphere (winter season for the southern hemisphere). What ultimately determines the seasonal conditions is the maximum angle of the sun above the horizon at midday and the total hours of daylight.

The earth to sun distance has only a minor influence on our seasonal conditions. At aphelion the sun will be at a distance of 152,102,140 km. This is only 4,996,419 km farther from the sun than we were on January 3, when we were at perihelion (closest to the sun), giving a difference of about 3.3 percent in distance.

Clear Skies

Ted Bronson