Solstice and Super Moon: Transitions

We have two special moments this week in the heavens, moments that attract public attention because they are transition points in the cycles of nature. As Earth orbits the Sun, and the Moon orbits the Earth, we are aware of changes in the relationship between these bodies, and the special alignments that come and go. This week, we experience the Summer Solstice in the northern hemisphere, and also a Super Moon, a full moon that coincides with the closest approach of the Moon to Earth.

Solstice is a special moment, driven by the Earth's tilt with respect to its orbit around the Sun. The 23 degree tilt of Earth's axis brings about considerable change in the length of time the Sun is above the horizon, and obviously that affects weather, and affects how people live, in particular in northern latitudes. Solstice marks the seasonal shift from lengthening days to shortening days. June 21st marks the moment this year when that happens.

Super Moons are a popular thing now, and this too marks a special moment, a transition in the Moon's orbit around the Earth when the Moon reaches the closest point on its elliptical path, and appears larger in the sky. Along with the somewhat larger size in the sky comes an increased impact on tides, and groups such as the California King Tides Initiative have worked to raise awareness of global warming by measuring the impact of high tides on coastal communities. This month's Super Moon occurs on the night of Saturday June 22nd to the morning of Sunday June 23nd, when the Moon reaches perigee (closest approach to Earth) within a few minutes of the moment of Full Moon.

The heavens are full of moving objects, from the planets in the Solar System, to asteroids and comets, and even galaxies and stars. All of this motion creates patterns and alignments that are beautiful to behold. And the transitions between key alignments make for interesting moments to ponder our place in the universe.

Hercules

The Stars of Hercules

The early summer skies feature a fascinating constellation that climbs high into the night sky and provides several interesting features to see with the naked eye, binoculars or a telescope. Hercules is the Roman mythological hero that is adapted from the Greek hero Heracles. In the night sky, he is kneeling in the sky with a club overhead, engaged in battle with other mythological enemies throughout the heavens. Similar to Orion the Hunter, Hercules has a distinctive shape; in stark contrast to Orion, Hercules has no bright stars - no first magnitude stars, and only one that is barely second magnitude, and hence Hercules takes some effort to find. But it's worth the effort.

Hercules is visible due east after sunset in June, and is directly overhead by midnight. The middle four stars form a distinctive shape, well known to astronomers as the Keystone. This trapezoidal shape is the center of the figure of Hercules, and it contains a beautiful deep space object known as Messier 13, the Great Globular Cluster in Hercules. It is a spectacular sight to behold in binoculars or a telescope; M13 is a rich cluster that shimmers from the 300,000 stars located in it.

The stars of Hercules are not particularly bright, but they are quite interesting. One of the brightest stars is called Rasalgethi, and it is a a binary star system with a red giant star and a companion that orbit each other every 3,600 years. The brightest star is called Kornephoros, a yellow giant star 148 light years from Earth.

Exploring the heavens is more fun when you know what to look for. Spend a few minutes on Hercules with a telescope or binoculars, and you'll see plenty of interesting objects, even from within a big city.

Image courtesy of SkySafari.

Transitions in the Evening Twilight

Every night, the sky appears a bit different to us, and in June as the long days of summer unfold, the sunset sky changes more rapidly than usual. The trio of planets that dominated dusk are now a pair, as Mercury and Venus climb higher into the west, and the bright stars and constellations of winter rapidly fade from view.

June's evening sky

The bright twin stars Castor and Pollux in the constellation Gemini are dropping gradually into the western sky after sunset, and the later and later onset of darkness combine with the change in position to speed these two stars out of view over the coming days. As they are lower and lower each night, Venus and Mercury will move higher each night and over the next 3 weeks, they will move closer to each other.

As you watch the changing landscape in June, take note of the gradual slowing in the onset of darkness as we approach the summer solstice later this month. The evening sky is a beautiful place to see transitions, and the visiting planets this month provide a fine guideline for this.

The Dance of the Planets - a spectacular celestial alignment

This week is the culmination of a spectacular celestial alignment, creating a rare and beautiful triangle of three planets on Sunday 26th. The planets will be low in the west after sunset, and as the glare of the sunset fades, the three bright dots of light will emerge from that glare, and if you have a good western view, you'll see them for a short window of time before they set.

The Triangle of Planets

Jupiter has been dominating the night sky for months, but each successive night has brought it closer to the time when it slips 'behind' the Sun, from our vantage point, and is shielded from our view. This happens to all of the outer planets throughout the course of a year or two. But by cosmic coincidence, Mercury and Venus are rapidly rising into the sunset sky, as their orbits bring them out of the glare from being 'behind' the Sun, and they quickly pop up into the evening sky. This week, they appear to move higher and higher in the sky just as Jupiter is 'falling' and they cross over in a lovely pattern.

To see this spectacle, head out any evening and look west. The configuration will be changing noticeably each night, and for me, that is the real fun here -- to not only see a rare and unusual alignment on Sunday, but to watch the set up in the days before and after. Here are a number of good links with additional information:

Sky & Telescope Magazine
The Always-Engaging Tony Flanders on SkyWeek
NASA Science Cast

Enjoy the show, and may you have clear skies!

Image courtesy of Sky & Telescope

Planetary Trio 'Warm Up Act'

During the month of May, three planets are going to move into a very close alignment, and the set up begins this week with the Moon adding some color to the scene for a few days. The two fast-moving inner planets, Mercury and Venus, are going to be coming into view in the west shortly after sunset, joining the massive Jupiter as it slowly fades out of view into the twilight. The dynamics of these changes is not easy to explain in a short blog post, but because of the fact that inner and outer planets appear to move differently from our Earth-bound perspective, the planets will all appear to 'cross over' in the west over the next few weeks, and the view should be dramatic.

The Moon adds color to the view.

This weekend, the show starts with Venus emerging from the glare of sunset into the western sky. You'll need a low western horizon to see this, in particular with the young Moon on the 10th. The alignment of Jupiter, the Moon and Venus on the 11th should be nice, and then as the Moon rapidly moves out of the scene, look for Venus (and shortly thereafter Mercury) to move up higher and higher in the twilight sky, leading to a much more spectacular lineup. More on that in my next blog post.

Image courtesy of Sky & Telescope.

SkyWeek video - an excellent online astronomy resource

There are many astronomy resources on the web that help you to better understand the night sky. One of the finest is the 5 minute video from Sky & Telescope Magazine entitled SkyWeek. Hosted by associate editor Tony Flanders, I find these weekly videos to be quite illuminating, combining the highlights of the night sky with science and understanding of the things you are seeing. Tony delivers all of this with a great sense of wonder and enthusiasm, without talking down to the audience. I always feel like I am being taught something new and interesting, combining simple observations with deeper astrophysics.

I had the pleasure of spending time with Tony and his family while on an eclipse expedition several years ago, and I really liked how he could balance the far ends of the spectrum of observational astronomy and astrophysics. He has been creating SkyWeek episodes for about one and a half years, and I hope he continues for a long time into the future. The show is carried on many PBS affiliates, adding considerable depth to the quality educational lineup available on public television.

Click here to view.

Saturn at Opposition 2013

Typical Telescope View of Saturn

Saturn reaches a special moment in the sky for us Earth-bound viewers, a time when conditions are most favorable for viewing the 2nd largest planet in the Solar System in all its glory. Opposition is the time when the planet is directly opposite the Sun, from our Earthly point of view. That means a few things: (a) it is at its closest to Earth, and therefore brightest for the year, (b) it is visible all night, rising just after sunset and setting just before sunrise, and (c) it is illuminated straight overhead from the Sun, much in the way we view a full moon.

For the city dweller, Saturn is an easy object to find, outshining most of the stars in the sky except nearby Arcturus, and its rival planet Jupiter (which is slowly fading into the west earlier each night). Saturn glows a yellow-white hue, in contrast to another nearby bright star, Spica. To find Saturn, it rises right after sunset this evening and for the foreseeable future, and glides from the south-east to the southern sky, and then across to the south-west after midnight.

If you have a telescope, now is the time to put it to work, as the view of Saturn will be at its finest. Wait a little while after sunset until Saturn is higher in the sky, less susceptible to atmospheric effects. The ring system is tilted 18 degrees toward Earth, so the view is quite good, and as anyone who has seen Saturn in a telescope will attest, the rings are amazing to see with your own eyes.

Here are two good resources for learning more about Saturn at opposition: Sky and Telescope's fine article, and EarthSky's tips how to find Saturn using the Big Dipper, Arcturus and Spica.

Image courtesy Wikimedia Commons

Moon Musings

Lunar Terminator

As the Moon reaches first quarter phase, I find myself drawn to the Moon's 'terminator', the line that separates dark from light. At first quarter phase (happening this week), the Moon presents Earth a very fine view of the terminator, exposing the highs and lows of the surface of the Moon. As I regularly point out to people during star parties, the region of the terminator during the waxing phase of the Moon is the region of sunrise, the place on the Moon where the Sun is just emerging above the horizon for what will eventually be a long lunar day (this takes 29 'Earth-days' to complete). As such, the illumination on the Moon's surface is much like you would expect on Earth at sunrise: long shadows across the land, with unusual features such as valleys and mountains being partially illuminated. The image attached (courtesy of APOD) shows the view through a telescope of the terminator, with shadows clearly visible in the craters and from the peaks of the mountains.

Tonight will be a fine time to peer at the Moon with anything you have at your disposal. It's the easiest target to find with a telescope or binoculars, and it's always visible even in the worst city lights. And it's a treat to see something unusual yet familiar, the sight of sunrise on another world.