Observing Twilight into Dusk

The minutes after sunset are some of the most beautiful, as the last rays of sunlight have disappeared and the sky begins its daily transition from bright blue to dark night. Looking west after sunset in the early days of Fall, you quickly find Arcturus shining due west, at first looking almost like an airplane that is moving very slowly. But soon you realize that this is a star, the third-brightest in the heavens. It is bright enough to shine clearly through the glow of twilight. The colors of the sky are changing rapidly during twilight, and the brightest stars soon emerge. In late September, you can easily find the fifth-brightest star in the heavens, Vega, directly overhead, guiding you to its neighbors Deneb and Altair in the Summer Triangle. And looking back toward the western horizon where Arcturus is shining, you can soon find the red supergiant star Antares shining low to the left (south-west) of Arcturus.

Later this week, the young Moon arrives in the twilight sky and passes near Antares. Find a nice western horizon, get comfortable, and enjoy the evening show that is pleasant, relaxing and beautiful to see.

Image courtesy of Sky & Telescope Magazine.

Celestial Companions in the Cold Dark Morning

January mornings are dark times, and when the sky is clear it is certain to be chilly outside. So I find the sight of the old Moon reassuring, a warm light that fades a bit each successive morning and guides the way through bright stars and planets along the ecliptic to the soon-to-be-rising-Sun. You can see this spectacle at its finest the next few mornings as the Moon moves a bit further eastward each day and passes near to some distinct celestial companions.

The Moon is passing now through Scorpius and the grey-white of the Moon stands in stark contrast to the red-orange of the star at the heart of the Scorpion, Antares. Moving close to Antares on Friday morning, the Moon continues toward the brilliant planet Venus on Saturday morning, and then slowly fades into the glare of sunrise on Sunday morning. My kitchen window faces south-east so I see this changing landscape each morning and I look forward to the coming days with clear skies in the forecast. If you rise before sunrise, take a moment to look out toward the south-east and enjoy the calm of this morning celestial grouping of close companions in the heavens.

Blue Star, Red Star, Yellow Star

When conducting a star party, I always point out star colors. Most of the time, people see the stars as uniformly white, but in fact upon closer inspection it's easy to see that stars have color, sometimes very dramatic color. This time of year there are several colorful bright stars that illustrate nicely the range of what you can see in the sky.

The southern sky is dominated by the distinctive shape of Scorpius, the Scorpion of the Zodiac constellations. The "heart" of this constellation is the bright red supergiant star Antares. It is in the middle of the body of the scorpion and it is one of the biggest stars we can see, so big that if places in the Solar System it would enclose Mercury, Venus, Earth and Mars. To the observer, it looks a reddish-orange color.

High above this time of year is the Summer Triangle, featuring three of the brightest stars in the sky. One of these three is Deneb in the constellation Cygnus, the "Northern Cross." Deneb appears blue to the observer and in fact is indeed a blue-white supergiant star, similar to Antares in terms of massive size, brightness and distance from the Sun.

These two beautiful stars should be enough to whet your appetite for detail when you look at the night sky. They are bright enough and easy to spot and display color quite nicely. But don't stop there. A simple pair of binoculars gets you enough resolution to see an amazing array of color in so many of the stars in the sky.

The colors of the stars is an indication of their temperature. Like the different levels of heat in flame, the colors of stars follows a similar pattern with red being cooler and blue being hotter. There are yellow stars, hotter than the red giants, and next in line are white stars, cooler than the blue stars. Details of Stellar Classification and Color Index are documented on very fine websites for those who want to learn more about star colors.

Scorpius now in view

The summer constellation Scorpius is now center-stage in the southern sky. It's always a treat to see the distinctive shape of Scorpius with red supergiant star Antares glowing in the sky. Through binoculars Scorpius is great because of an abundance of deep-sky objects in and near the constellation. And this week there is an extra treat as the moon passes through.