The Constellation Virgo

Late spring and summer skies are dominated by the big constellation Virgo, the Maiden. This grouping of stars is the second largest in the night sky (after Hydra), and includes the first magnitude star Spica, the double star system Porrima, and the Virgo Cluster, a region of the universe that has 1000s of galaxies in one place. [More on the Virgo Cluster and Supercluster in a future post]

The Constellation Virgo

A member of the 12-constellation zodiac, Virgo is directly in the path of the Moon, Sun and planets and consequently is host to wandering celestial objects. Now and for the coming months, bright orange Mars is passing through the constellation en route to a mid-July rendezvous with Spica. In mythology, the constellation represents a woman in the sky, but the identity is different depending on whether you read the Babylonian, Roman or Greek interpretation. And in any case, I find it quite difficult to see a distinctive pattern from the stars in Virgo. Nonetheless, it is a fascinating place in the sky, because it contains the Virgo Cluster of galaxies with notable telescope objects such as M86 and M87 and the magnificent Sombrero Galaxy.

Virgo occupies an interesting space in the sky, the First Point of Libra, a place where the Ecliptic (path of the planets and Moon) crosses the Celestial Equator (dividing line between the northern and southern hemispheres in the heavens). The Sun's arrival at the First Point of Libra marks the first day of Autumn in the northern hemisphere (Autumnal Equinox). The reason why this spot is called the First Point of Libra is that thousands of years ago the intersection of the Ecliptic and Celestial Equator was in the constellation Libra, but the effects of precession have moved that point from Libra to Virgo, and in 400 years that will move into the next zodiac constellation, Leo.

From city limits you can certainly find Spica, Porrima and for the next few months, brilliant orange Mars in Virgo. With binoculars you can gaze into the heart of the Virgo Cluster and although you won't see The Big Picture with 1000s of galaxies, you will certainly see a richness of stars and know that you are seeing light that is at the center of our own supercluster of galaxies that define our corner of the universe.

Images courtesy of Wikimedia Commons

Possible New Meteor Shower

Meteors are a delight to see in the night sky, appearing without warning and gracing the sky with their shimmer and speed, playful fireworks that quietly captivate those who take the time to watch. Annually there are many meteor showers that we can predict and prepare for, primarily because they are caused by debris in the path of Earth's orbit and are reliably there each time Earth passes through the debris. In most cases "debris" means the small particles of dust no larger than a grain of sand, left in the wake of a comet or asteroid.

Radiant in Camelopardalis

Friday night May 23 through Saturday morning May 24, Earth will travel through such a stream for the first time from a source that we have not encountered before. In this case it's Comet 209P/LINEAR, a fairly unimpressive comet from a visual point of view, but one that has left a debris stream in its wake and could be have initiated a new meteor shower. The peak for this will be Friday night / Saturday morning around 1:00 am pacific time, so find a dark spot with a clear sky, give your eyes time to adapt, and enjoy. You don't need a telescope or binoculars. The 'radiant' point of the shower is in the faint constellation Camelopardalis (see image) but you don't need to face that way - just have a clear sky and a good view overhead, a lawn chair or pad to relax on.

More information on the following sites:

Spaceweather.com 
Sky & Telescope
EarthSky.org

Image courtesy of Sky & Telescope.

Four Planets at Dusk

As the Sun sets this week, we have a very nice view of four planets visible in an arc that spans the entire sky. About 45 minutes after sunset the sky is nicely fading to dark (around 8:45 to 9:00 here in San Francisco) and the four brightest objects in the sky take the stage, spanning from the northwest to the southeast. Nearest to the Sun is elusive Mercury in the northwest evening sky above the sunset point. Looking up and to the left you can't miss brilliant Jupiter, gradually dropping lower and lower in the evening sky in the constellation Gemini. Higher up and farther to the left of Jupiter is orange Mars, shining among the bright stars of Virgo. And finally in the opposite side of the sky from sunset is Saturn, emerging from opposition in the southeast part of the sky among the faint stars of Libra. From horizon to horizon the planets dominate the dusk sky, so if you have a good horizon step outside as the sky is fading and enjoy the four bright pinpoints of light that mark the path of the Solar System. In the fading light of dusk these are the first four objects you will be able to easily spot.

More details on Sky & Telescope and on Earth Sky.

Urban Astronomy in the Southern Hemisphere

Australian Flag

This week I had the privilege of working for four days in Sydney, Australia and the weather was clear, so I had a chance to experience the daytime and nighttime sky from a wholly new perspective. When you view the sky from south of the equator the sky is viewed in an entirely new light, and the differences in view in the southern hemisphere compared to the northern hemisphere are many.

Daytime: in Sydney, the Sun tracks across the northern half of the sky, not the southern. In San Francisco we know that the southern exposure of a building or garden gets more Sun, but in Sydney the northern exposure gets all the Sun. When you are simply walking around the city the effect is incredibly subtle. But for me as an amateur astronomer, it was disorienting at times. I enjoyed the experience of looking for shadows and light in a new way and had to think through why and how light and shadows appeared as they did. 

Nighttime: this is where the Southern Hemisphere is amazing. At night the entire sky feels new. I was in Sydney all week and had to put up with city lights and a bright Moon, so that afforded me a chance to get introduced to only some of the night sky with just the brighter objects available for viewing. Nighttime urban viewing presented me with four levels of discovery. 

1. Uniquely southern stars and constellations 

The immediate thing one notices in the southern sky is the Southern Cross and the two ‘pointers’ in Centaurus, Alpha Centauri (Rigil Kent) and Beta Centauri (Hadar). This bright grouping is high in the south in May. There are other nearby constellations that are fainter in an urban setting, but the Southern Cross (Crux) and Centaurus are very obvious, and to my eye are the most unusual and captivating objects. The Southern Cross is so special to the region, it is prominently featured on the Australian and New Zealand flags. 

2. Ecliptic / Moon and Planets / Zodiac 

In stark contrast to my view of the sky in San Francisco, the ecliptic traverses not the southern sky but the northern sky from Sydney, and the zodiac constellations on the ecliptic are quite differently positioned. For example, Scorpius and Sagittarius are summer constellations from my home in San Francisco and are low on the horizon, never getting too high in the sky on summer evenings. From Sydney, these two constellations are much higher in the sky and are upside-down from my point of view. The Moon and planets, by virtue of their following the same ecliptic track across the sky, are disorientingly located in the north, again breaking convention and obligating the studied observer to rethink his bearings. 

3. Equatorial constellations viewed from the south 

The region on and near the celestial equator is lined with bright stars and well-known constellations. We normally view this in the northern hemisphere looking toward the south so equatorial constellations such as Orion have a definite ‘up’ and ‘down’ that we expect. When you move to the southern hemisphere, the view of the celestial equator and its constellations in inverted so all of the familiar patterns are no longer so familiar, and you have to be creative to see the same images presented that way. 

4. Uniquely southern objects 

Jewel Box Cluster

Although my experience was an urban one, I did see some special objects. Alpha Centauri itself is a good telescopic object, as it is actually a double star system and at the Sydney Observatory I had a nice view of this through a 14 inch telescope there. Also, the amazing Jewel Box Cluster is a great open cluster that is quite striking through binoculars or a telescope. 

The two things I would have liked to see were the Large and Small Magellanic Clouds, nearby dwarf galaxies that are large and impressive, but easily washed out in the light of the city and a full moon. That will have to wait for my next trip to Australia and for that one, I’ll plan a night out in the country to see the true depths of the southern Milky Way and the Magellanic Clouds. For now, I am extremely satisfied with the chance to have seen the overall change in perspective in the southern hemisphere, and of course the bright stars of Centaurus, the Southern Cross, and the Jewel Box Cluster. 

Saturn Arrives / Mars Reverses Course

Mars in Retrograde

It's a good time to enjoy planets, as Mercury, Jupiter, Mars and Saturn all occupy the May skies. Saturn reaches opposition on May 10, rising as the Sun sets and remaining visible all night next to the bright pair of stars that top the scales of Libra.

Mars has been in retrograde motion (reverse motion) across the constellation Virgo during April and in early May reaches the end of retrograde and returns to prograde motion, moving back toward the bright star Spica. It's interesting that Mars was near Spica during April's 'Blood Moon' eclipse and in the course of a few weeks moved rapidly westward toward the star Porrima. Now that it has completed its retrograde sweep it returns to Spica in July and continues eastward toward a conjunction with Saturn in Libra in August.

Image courtesy Sky Safari.