Vernal Equinox, Full Moon, Passover and Easter

As Spring arrives, so do the religious festivals of Passover and Easter. These two festivals change date each year, happening sometime in March or April. These festivals are tied to the phase of the Moon and the Vernal Equinox (the first day of Spring), and hence they change date each year. Tonight's Full Moon is the event that ushers in these festivals. How does the timing of these events work?

The Vernal Equinox is the first day of Spring, the day when the Earth's tilt is aligned to its orbit around the Sun, so the poles of the Earth tilt neither toward the Sun or away from the Sun. On this day (and again in the Fall at the Autumnal Equinox), every place on Earth experiences the same number of hours of Sun above the horizon and Sun below the horizon, hence 'equinox' for equal lengths of day and night.

The first Full Moon following the Vernal Equinox marks the start of the religious festivals in Judaism and Christianity, with Passover taking place on the day of the Full Moon (today), and Easter on the first Sunday following the Full Moon (this Sunday April 8th).

Tonight's Full Moon will be very close to the bright blue star Spica, the brightest star in Virgo, and just to the left of Spica you will have a nice view of the planet Saturn. Enjoy the view!

Image courtesy of Sky & Telescope Magazine.

Young Moon, Jupiter and Venus shine in the West

The next few evenings feature a beautiful alignment of the two bright planets Venus and Jupiter, and the young Moon as it starts its monthly journey around the Zodiac. Every 29 days, the Moon makes a 1.6 million mile journey around the Earth, and as it does, it travels across the entire Zodiac, the band of constellations through which the Sun and planets appear to "travel" around our nighttime sky. Each month following the New Moon phase, the young Moon slips quietly into the evening sky, first appearing near the horizon as a thin sliver of light, and each night growing in size and distance from the setting Sun. This month, with Jupiter and Venus in close proximity, the changing view from one night to the next promises to be beautiful. Now all we need in San Francisco is clear skies!

Image courtesy of Sky & Telescope.

Ring of Fire Roadtrip and the San Francisco Amateur Astronomers

In just two months, the western United States will witness a special astronomical event, a "Ring of Fire" solar eclipse, also called an Annular Solar Eclipse. This particular kind of eclipse is the result of an exact alignment of the Sun, Moon and Earth, but unlike a Total Solar Eclipse in which the sky turns to night and the Sun's corona becomes visible, an Annular Eclipse brings us a different spectacle in which the inner 90% of the Sun is blocked out by the Moon, leaving an eerie "Ring of Fire" in the sky.

The event takes place on Sunday May 20th and although San Francisco and many parts of the western US will see a very deep Partial Solar Eclipse, you will have to travel to Northern California to see the full 'Annular' effect in which the Moon is centered in the disk of the Sun. 

My local astronomy club, the San Francisco Amateur Astronomers, is sponsoring a "Ring of Fire Road Trip" for those who'd like to join the club and view the May 20th eclipse from the Mt. Shasta area, several hours north of San Francisco. If you'd like to learn more about this, check out the newly-redesigned SFAA website and make plans to see this special event. 

By the way, the SFAA conducts monthly lectures, star parties and special events like the Ring of Fire Roadtrip. Check out the website for the latest events, including a lecture this Wednesday March 21 by NASA Astronomer Jeffrey Van Cleve on the topic of Near Earth Objects. Most SFAA events are open to the public and we welcome you to join us for a talk, a road trip, or a night under the stars at one of our upcoming Star Parties in San Francisco or high atop the fog on Mt. Tam, about 45 minutes north of San Francisco.  

I hope to see you at an upcoming event. 

Image courtesy of Wikimedia Commons / Sancho Panza.

Jupiter and Venus in Conjunction

The gradual changes that occur in the night sky are generally imperceptible to all but the most thorough observer. So at special times like this week, when we have a close-encounter of two of the brightest objects in the sky, we are able to see the grand pace of the Solar System at work in our own backyards. Jupiter and Venus, the two brightest objects in the night sky after the Sun and Moon, reach conjunction this week and fill the western sky with their brilliance. The chart shows the relative change each night, as Venus, much closer to the Earth, swings around in its orbit higher into our evening sky, while distant Jupiter drops a bit lower each night in comparison. It's one of those times that it will be very obvious and easy to see the change of planetary position from one night to the next.

Image courtesy of Sky and Telescope Magazine.

Mars at Opposition

Tonight Mars is at opposition, a once-every-25-month event in which Earth passes between the Sun and Mars, and we observe Mars at its closest approach. The patterns of alignments of the Earth with different planets is a very cyclical event, every year or two depending upon the proximity of Earth to that planet.

The relative distance from Earth to Mars at each opposition is also something that is quite cyclical. You might recall in 2003 claims that the "Mars is going to be as big as the full Moon" during that year's very favorable opposition. In fact, the disk of Mars was never that big, but hype aside, Mars appeared quite large compared to any other time in recent history. In 2012, opposition brings us Mars as a bright orange star in the east shortly after sunset, traveling across our night sky from horizon to horizon. Although it is at the closest until 2014, it is just a small dot of color through most home-based telescopes. You will need considerable power to see the polar ice caps and other surface features (such as in the photograph). My friends in the San Francisco Amateur Astronomers (SFAA) club live for such moments, and if you can visit a local observatory or visit a star party this time of year, I am sure Mars will be one of the highlights.

The next time Mars nears the size of its famous 2003 opposition is in 2018. Until then, enjoy Mars however big or small it looks. It's a fascinating planet.

Photo by Mark Killion.

Get Involved: Dark Skies

As an Urban Astronomer, I am enthusiastic about astronomy even in the light-polluted urban centers of the world, including my own city of San Francisco. I write this blog for many reasons, one of which is to remind city dwellers that there is still plenty to see in the night sky. Right here in San Francisco, there are ways to view the sky in a dark spot, away from streetlights and brightly-lit areas of the City, and see quite a bit of the night sky. Mainly you just need patience to let your eyes dark adapt your location, and before you know it you can find quite a few stars and constellations.

Over the past weeks, I was traveling in and around Flagstaff, AZ, the World's First International Dark Sky City. Flagstaff is a medium-size city of about 60,000 people, but through smart street lighting, has reduced its light output considerably. While visiting Lowell Observatory on a hill above Flagstaff, you could see the city lights below, but it was not like any other I had seen. Clearly there was light from the city, but it was subdued, not shining up in the sky but rather shining down onto the streets and public spaces. That is Smart Lighting!

There is a global organization called the International Dark-Sky Association that provides advocacy and education to support communities and municipalities around the world to learn about smart lighting and preservation of dark skies. I applaud their efforts and their mission. Locally in San Francisco fellow SFAA member Dave Goggin has organized a list and invites participation in San Francisco discussions about lighting.

What can you do in your community to preserve dark skies? I am sure the Dark Sky Association would welcome your participation. It's a very grass roots thing. Here is an article about an individual in San Clemente starting a movement there. Get inspired!

Jupiter, Venus and the Moon grace the Evening Sky

The Moon, Venus and Jupiter, the three most dominant objects in the night sky, will form a number of beautiful patters to grace the evening sky in the coming days. Venus and Jupiter have become so dominant in the west after sunset each night that you cannot help but notice them shining like diamonds, and as we enter a new lunar cycle, the young Moon creates beautiful patterns as the daily change in relative position makes for an exciting night sky. Things will get even more exciting next month when Venus and Jupiter reach conjunction, when they are at their closest alignment.

Image courtesy of Sky & Telescope Magazine.

Auriga and Capella: the Galactic Anticenter

High overhead in the winter sky is the distinctive constellation Auriga the Charioteer. This is a bright constellation, visible even with city lights, punctuated by the 6th brightest star in the night sky, Capella. To the casual viewer, Auriga appears to be a pentagon in the sky, and in winter it is nearly directly overhead as night sets in. Depending upon the source, the constellation Auriga is described as the actual Charioteer holding a goat, or just the shape of his pointed  helmet. The star name Capella is in fact Latin for 'small goat.'

Auriga has the distinction of being located in the direction of the Galactic Anticenter. What is an anticenter? It is the point in the night sky that is opposite the Galactic Center, of course :-)  The center of the Milky Way Galaxy is located in the direction of the constellation Sagittarius, a dominant summertime constellation. So not surprising, in the winter time when we are looking the 'other direction' in the sky, we find ourselves staring out into space directly out of our Milky Way Galaxy.

The bright star Capella is relatively close to Earth, 42 light years away. It shines brightly in the winter sky, making Auriga easy to locate. A fascinating fact is that the star Capella is not one star, but a four-star system made up of two binary stars. That means, that the four stars are broken into two pairs of binary star systems. Two of them are big stars, 10 times the size of our Sun. The other two are quite small and faint, so when you see Capella you are primarily seeing the two bigger stars. Some binary star systems can be seen as separate stars in small telescopes or binoculars, but the two bigger stars in the Capella system are too close to see as separate objects.

Try to locate Auriga and Capella tonight and savor the fact that you are staring out of the Milky Way into the vastness of space far away from our home galaxy.