Dark October Mornings

Last year the US Congress made a change in daylight savings time. Rather than end in October it now carries into November. The effect of this is that mornings are dark in October, making it hard to get up and get going. On the other hand, it makes it much easier to see the morning sky and in the coming days it's going to be noteworthy.

Sunrise is happening this week at 7:30 which means that up until 6:45 or so, the sky is dark enough to see stars and planets. The diagram shows where to look for the Moon, Saturn and even Mercury. In the Fall, the path of the planets and Moon (the ecliptic) is in a very steep line from the point of sunrise into the eastern sky. Hence Mercury will be visible just above the point where the Sun will be rising, and Saturn and the Moon in increasing distances above and to the south of Mercury.

I love to see the very old Moon in the last days of its cycle. The ever thinning crescent reflects more and more "earthshine" and glows like a jewel in the morning sky. As October comes to a close, the waning Moon on the 24th, 25th, 26th and 27th should be a striking sight as the sky begins to glow with the dawn.

Galileo discoveries redux

Nearly 400 years ago Galileo pointed a crude telescope toward the heavens and documented three remarkable things in the sky, discoveries that dramatically affected the understanding of the universe at that stage in history. With his telescope Galileo was able to see that the Moon was not a perfect circle, that Venus had phases, and that Jupiter had satellites of its own. Each of these posed a threat to the current body of knowledge of that era - Jupiter's moons and Venus' phases challenged the geocentric view of the universe and the non-perfect Moon challenged the Aristotelian theory of perfectly circular shapes in the universe.

With a simple telescope or even binoculars you can recreate some of these discoveries in the coming weeks and months. I'll write more about Venus in a future post. In October and November the phase of Venus will gradually transition from gibbous to half and later in the year to a crescent. The Moon is easy enough to study and is a marvel to view in any telescope or binoculars with the spectacular rocky edge of the surface always intriguing.

However, for the coming months Jupiter is the dominant "star" in the evening sky. Jupiter calls out for investigation because of the interesting texture of its surface and because of the changing position of its four largest moons. Called the Galilean satellites, these moons are visible to us even in low magnification and are interesting to observe because they change location so quickly -- even within the course of a few hours. They regularly pass through the shadow of Jupiter, yielding eclipses on a frequent basis.

From the nearest to the furthest moon, the names of the four satellites are Io, Europa, Ganymede and Callisto. Io is so close to Jupiter that it orbits the giant planet in less than two Earth days. Europa takes exactly twice as long and Ganymede twice as long again. Every few hours the overall pattern of these four moons is changed sufficiently to see new moons emerge from behind Jupiter, others disappear, and the overall pattern spread apart and then contract into a group.

Sky and Telescope Magazine has an excellent article on the moons and a very helpful pop-up screen that you can view in your web browser. It shows you the relative position of the moons of Jupiter at any time and can make a star gazing evening into a treasure hunt that will give you the feeling of discovery that will rival that of Galileo. So take the time to look to the south for the brightest object you can see (about halfway up the horizon above due south after sunset) and try it for yourself.