Geminid Meteor Shower 2011

The Geminids peak the nights of December 13th and 14th this year, one of the better meteor showers of the year. Unfortunately for 2011, most of the Geminids will be nearly invisible due to the very bright Moon that dominates the late night and early morning sky, when the Geminids are at their best.

The effect of a bright Moon on a meteor shower was vividly illustrated to me during the Total Lunar Eclipse a few days ago. I was at Ocean Beach on the west coast of San Francisco for the eclipse in the early morning hours. Facing west, Gemini was directly in front of us, dominating the western sky. As the brightness of the Moon faded, we began to notice meteors -- we were seeing some very early Geminid meteors, facing the radiant directly. I was very surprised at the stark contrast in meteor visibility from Full Moon before the eclipse started, to an ever-increasing amount of meteors over a very short period of time as the Moon, in effect, when through all of its phases in about 60 minutes. It reaffirms for me the huge difference a moonlit night makes when watching a meteor shower.

Although the meteors will be diminished for the Geminid Meteor Shower in 2011, I'll still take a look, since a big shower like this has plenty of bright meteors that pierce the night despite moonlight. If you want to read more about the Geminids, check out this interesting article about the Geminids radiant, from Earth Sky, from the LA Times, or this one from NASA Science News.

Image courtesy EarthSky.

Total Lunar Eclipse 2011 - in San Francisco

Saturday morning, we will witness a Total Lunar Eclipse visible from western North America and regions across the Pacific Ocean. In San Francisco, we will have a dramatic early morning spectacle of the fully eclipsed Moon setting on the Pacific just as dawn breaks. As with any total lunar eclipse, the Moon's surface will be completely covered by the dark 'umbral' shadow of the Earth, but it will remain visible, taking on an eerie appearance of rusty red, or deep grey, or a mix of colors. Every eclipse is a little bit different, so we wait in anticipation to see what happens Saturday morning.

The circumstances of this eclipse are outlined in detail in this informative Sky & Telescope article, and this excellent NASA Science News article.

The timeline for San Francisco (and the entire pacific time zone) are: start of eclipse at 4:45 am, start of totality at 6:05 am, and end of totality at 6:57 am. The glow of the dawn sky will emerge in the eastern sky shortly after 6:00 am, so the Moon will be in total eclipse as the sky begins to brighten, and by the time the Moon exits the total phase, the sky will be fully lit in advance of the sunrise at 7:13 am.

What does all this mean to the casual viewer? You will experience the best views and the most drama from 4:45 am until 6:30 am, when the Moon gradually changes from full to completely eclipsed, and the skies are dark enough to appreciate the beauty and subtlety of the lighting and color of the lunar surface. And as the Moon's brightness is attenuated as the Earth's shadow creeps across the surface, the backdrop of stars will begin to shine more brightly by contrast, revealing the wonderful winter sky at its best, with the constellations Taurus, Orion and Auriga around the Moon, and some of the most beautiful, bright stars in the entire night sky punctuating the skyscape.

I welcome the public to stop by Ocean Beach on the west coast of San Francisco for an early-morning star party, where I and others from the San Francisco Amateur Astronomers (SFAA) will have telescopes set up for public viewing. We will set up at the beachwalk just across from the Beach Chalet restaurant on Great Highway, starting around 4:30 am. But heed the advice of Deborah Byrd in this EarthSky article, and wear very warm clothes. You'll be glad you did, as the winter chill is quite intense just before sunrise.

Jupiter at Opposition -- closest approach for 2011

The Autumn evening sky is being dominated by one bright, shiny object: the planet Jupiter, which will be a highlight for several months in our skies. On October 28th, Jupiter reaches "opposition" in which it is in a line with the Earth and Sun (and no, that is not what has been causing the recent earthquakes in the San Francisco Bay Area!).

Image Courtesy NASA

When Earth travels around in its orbit, approximately every 13 months we have a close encounter with Jupiter. When we do, the gas giant looks impressive with or without a telescope. Without a telescope, Jupiter is extremely bright, easily 50 times brighter than the brightest stars in the sky right now. It rises due East just after sunset, and remains visible the entire night. Through a small amateur telescope, Jupiter is a fine target, easy to locate and impressive with bands across its disk and the four Galilean moons shining brightly. Now is the time to get out a telescope or binoculars and share the brilliance of Jupiter with someone.

Orionid Meteor Shower 2011

The Orionid Meteor Shower peaks for the next two mornings, October 21 and 22, as the Earth passes through a debris stream left by Halley's Comet. Like all annual meteor showers, the Orionids occur at the same time each year because the Earth, in its 365-day trip around the Sun, passes through areas of increased debris, leading to a much more focused period of time with meteors flying into Earth's atmosphere and creating those beautiful streaks of light that magically light the sky for a moment and then vanish without a trace.

The name Orionids tells us that the meteors in this shower appear to emanate from the constellation Orion, the beautiful winter sky constellation. But like the best meteors in any shower, you won't see Orion until after midnight as it rises out of the east. Meteor showers are best observed between midnight and sunrise, when you are viewing meteors entering our atmosphere on the 'front face' of the Earth. Given that sunrise is quite late this time of year, take advantage of that and get up just ahead of dawn's light, around 6:15 in the San Francisco Bay Area.

Image courtesy of Earth Sky.

Autumnal Equinox: what do you see?

Friday September 23rd is the start of Fall here in the Northern Hemisphere, an event that has a specific moment, in this case 2:05 am on the West Coast. What happens at this moment? Can you 'see' an Equinox?

The two Solstices of the year, in December and June, get much more fanfare because they mark more dramatic transitions, both in the weather and in the slow change of the seasons. The longest day and shortest day of each year are much easier to understand. But the balance points in the equation of Earth's orbit, the Equinoxes, get much less attention because there is much less drama. But for me, there is a lot going on. From an observational point of view, there are three things to look for.

1. Sunrise is precisely due East and Sunset precisely due West, the two days of the year this happens.

2. The Sun is above the horizon 12 hours and below the horizon 12 hours (give or take a few minutes owing to the bending of light around the horizon as experienced at Sunrises and Sunsets).

3. The Sun's height in the sky at local noon, as measured in degrees above the southern horizon, is 90 degrees minus your latitude on Earth. For example, in San Francisco, we are about 38 degrees north of the equator, so the Sun's height at local noon is 90 - 38, or 52 degrees above the horizon.

There is a fourth, more subtle effect that happens around the time of the Equinox. The length of the day is changing most rapidly around this time. From the Summer Solstice to the Winter Solstice, the length of the day is continually reducing. On the Equinox, it is 12 hours, but from one day to the next the length changes about 2 1/2 minutes, around 16 minutes during the full week. That is noticeable, and if you get up at the same time each day, you are certainly aware of the changing light of the morning (or lack of light at this point in time).

The combination of the Earth's annual circuit around the Sun, the tilt of the Earth's axis, and the slightly eccentric orbit of the Earth around the Sun all contribute to very interesting effects that are most pronounced around the interesting transition points of Equinoxes and Solstices. Take a moment this Friday to appreciate what you are observing in the sky around you.

Big Astronomy Events in 2011 and 2012

Much of the time, I enjoy astronomy as a day-to-day hobby, taking in the sky often and enjoying the slowly changing view of the heavens. Sometimes, however, big events come along and obligate the observer to be present at a specific moment in time -- and also have the good luck of clear skies. We have a three such events in the coming year, and the San Francisco Bay Area is a good base from which to see these events.

1. Total Lunar Eclipse, December 10th, 2011.

This Lunar Eclipse will peak on Saturday morning, December 10th, just before sunrise here in San Francisco, meaning that if the skies are clear, the best view will be at the coast, where the Full Moon will be entering Total Eclipse just as it is setting over the Pacific. This will be impressive!

2. Annular Eclipse of the Sun, May 20th, 2012.

An Annular Eclipse, also called a "Ring of Fire" eclipse, happens when the Moon's disk fits "inside" the disk of the Sun, creating a ring of sunlight in the sky. It's not the same as a Total Solar Eclipse, but still a beautiful natural phenomena, one worth a trip to Northern California to see. The viewing path can be seen on the map in this link, and will pass near Redding and Mt. Shasta in Northern California. I'll be organizing a road trip with the San Francisco Amateur Astronomers (SFAA) to see this spectacle.

3. Transit of Venus, June 6, 2012.

A transit of a planet in front of the Sun is a rare and unusual event. This is one of a pair of transits of Venus, the first of which occurred in 2004, paired with this one in 2012. Then we have a 100-year gap until the next pair of transits of Venus. It will be a daytime event, of course, because we are going to see the tiny disk of Venus cross directly over the Sun's disk.

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I'll write about each of these events as the time draws nearer, so for now the main thing is to mark your calendar and do a bit of background reading by following the links in this blog post.

Image courtesy of NASA.

KFOG Podcast - July 8, 2011

Today was the final launch of the Space Shuttle. KFOG's Irish Greg and I talk about this historic event, about the wonders of the Summer night sky, and about upcoming Star Parties in the San Francisco Bay Area. All in 5 minutes! Listen here.

The Very Long-lasting Total Lunar Eclipse of 2011

On Wednesday June 15th, viewers in the eastern hemisphere will be treated to a very long-lasting Total Lunar Eclipse, a 100-minute marathon of an eclipse that will reveal the center of the Milky Way in the backdrop as the bright Moon is enveloped in the darkest part of Earth's shadow. Unfortunately for those of us on the other side of the Earth, including here in San Francisco, we will miss the entire eclipse. (But we will get a nice lunar eclipse later this year, on December 10th.)

As for June 15th, this particular Total Lunar Eclipse will be longer than most for two reasons, (a) the Moon passes nearly through the center of the Earth's shadow, and (b) the Moon is nearly at Apogee, when it is farthest from the Earth (and hence appears a bit smaller than usual and takes longer to pass through the Earth's shadow). For my colleagues in Germany, the Moon will rise already in mid-Eclipse, which is an outstanding sight that I have seen one time in the past. Moonrise will be at approximately 9:30 pm, and the Moon remains in total eclipse until approximately 11:00 pm. That would be something to enjoy from a spot with a good eastern horizon. For other locations around the world, use this chart from the NASA Eclipse Web Site to determine the timing for your location. I wish my friends on the other side of the world clear skies and happy viewing!

Take part in "The Globe At Night" project - just look up at the sky tonight!

For the next week everyone is invited to participate in a global effort to measure light pollution and to learn about stars and the sky in your neighborhood, especially for those in big cities like San Francisco. The "Globe At Night" project invites people from around the world to take a few minutes in the next 7 days and look at one of the most beautiful constellations in the sky, Orion, and simply report how much of it you can see. It's easier than you think. And it's a great family project to show kids what you can see in the night sky.

The Globe At Night website provides all of the details, but in summary you compare what you see in your sky (your backyard, rooftop or any other convenient observing location) to a series of images on the Globe At Night website. By finding the image that best matches your view and reporting this on the website, you are helping to gather data from cities around the world on the relative light pollution in the sky. The constellation Orion contains stars of varying brightness, and depending upon the darkness of your skies, you will see more or less of these stars. The charts on the Globe At Night website show you Orion with differing "magnitudes" of stars, so for very light polluted cities you might only see the 1st and 2nd magnitude stars, whereas in darker skies you will see 3rd, 4th, or even 5th and 6th magnitude stars (the higher the number, the fainter the star).

Join the worldwide "Citizen Scientists" supporting this effort to increase awareness of the night sky, and take part. And bring along a friend. It's fun!

The Winter Sky Beckons

The Winter Sky beckons me to stop what I am doing and pay attention, for the view of the heavens in this magical season is unlike any other. Here in San Francisco, when it is not raining (as was the case for most of January through today), the air is dry and the atmosphere clear, giving the casual observer sparkling vistas into the heavens. And as this kind of weather happens with regularity in the winter, and the hours of darkness are at their maximum, it is all but impossible to miss the winter sky.

Evenings right now are dominated by the slowly fading planet Jupiter high in the west at sunset, and the colorful bright stars of Orion high in the southern sky, Canis Major and Sirius to the lower left of Orion, and Taurus and Aldeberan to the upper right of Orion. Facing north, the Big Dipper and Cassiopeia trade places every 24 hours, circling Polaris, the North Star. And later in the night to the east are a variety of treasures in Virgo with Saturn in the vicinity. Two weeks ago the morning sky featured the old Moon passing through Scorpios and Sagittarius, creating beautiful alignments that accented the eastern horizon at dawn.

The most important thing to do, if you want to see these amazing sky spectacles, is to keep your eyes open and look up - - nothing more than that is necessary to be captivated by the spell of the sky. No need for a telescope or binoculars. This time of year the stars dazzle in the night, and appear to be asking all of us to take a moment to contemplate their majesty and come to appreciate the universe, awaiting your view each night of the year.

Quadrantids Meteor Shower - January 3-4, 2011

2011 starts with an impressive meteor shower for those ready to brave a cold night. The Quadrantids take place the night of Monday January 3rd into the morning of Tuesday January 4th, and are made better by the fact that the Moon is new, meaning no interference from moonlight.

As always, the best viewing of any meteor shower is from a dark location, ideally away from city lights. But I have had some success right in my backyard in San Francisco by positioning myself away from direct lights such as streetlights and houselights, and allowing myself 5 to 10 minutes to adapt to the darkness. Once dark adapted, the winter sky shimmers and Quadrantids are readily visible. In dark skies outside of cities you can expect up to 2 meteors per minute, but in the City I am happy to see 1 meteor every few minutes. This year should be as good a show as any, and despite our rainy Northern California weather the outlook is good.

To see this shower, position yourself facing northeast but give yourself as much of a view of the sky as possible. A lawn chair is best (along with blankets and a hat), as the meteors appear to originate in the constellation Bootes in the northeast part of the sky, but the meteors radiate in every direction away from this point.

For some fun background and history of this meteor shower, check out Astronomy.com and NASA's "What's Up" blog series. Image is courtesy of NASA.

Stay warm, and here's to good skies!

KFOG Podcast - December 3, 2010

Today on the KFOG Morning Show Podcast with Irish Greg, we talked about the discovery of new stars in the galaxy, alien life forms right here on Earth, the upcoming Geminids Meteor Shower on December 13-14, the upcoming Total Lunar Eclipse on December 20-21, and Holiday Shopping including a special 10% discount on anything at Scope City in San Francisco (my favorite place to shop) if you mention KFOG or The Urban Astronomer. Click here to listen. And take advantage of the 10% offer while it lasts!

Autumnal Equinox and the rate of change of the length of the day

Today is the Autumnal Equinox, one of two Equinoxes of the year. These are days that mark the transition from one season to the next, but also are days that have very special significance as the Earth orbits the Sun. Because of the tilt of the Earth's rotational axis, the Northern and Southern Hemispheres receive radically different amounts of sunlight from June through December, as the seasons progress from Summer to Fall to Winter (northern hemisphere). This is well understood and we learn from basic science courses that the in-between points while transitioning from Summer to Winter, for example, are the days that have equal periods of the Sun above the horizon and below the horizon -- equal duration of night and day -- hence Equinox. Today, everywhere on the planet, the Sun spent exactly 12 hours above the horizon and 12 below, and the Sun rose due East and set due West. From now through March, the Sun will be above the horizon more than 12 hours a day in the Southern Hemisphere, and less than 12 hours a day in the Northern Hemisphere.

I love the symmetry and simplicity of the Sun's motion on this day. It marks a transition as the days are getting shorter in the Northern Hemisphere. Everyone can feel the shortening of the days and sense, innately, that the changes in daylight and darkness are sudden and surprising. This is another fascinating change happening at the Equinox, more subtle but no less fascinating to me. When people sense the changes to the onset of darkness in the evening or the late sunrise in the morning, they are noticing that the length of the day is changing quite quickly and they feel that the times of day that might have been bright and sunny only a few weeks ago are now getting dark. At the time of the Equinox, the length of the day is changing most rapidly. For example, here in the San Francisco Bay Area, the longest day in summer is nearly 15 hours long and in winter the shortest day is approximately 9 1/2 hours. As the seasons change, the time of sunset and sunrise changes slowly, starting at the solstice in June - maybe only 1/2 to 1 minute per day. But then the changing becomes more rapid approaching the Equinox. At the time of the Equinox this week, the length of a day is changing 3 minutes per day -- that is, about 20 minutes in one week! So if you feel like the length of the days is changing very fast, you are absolutely correct.

The change is even more dramatic the farther north or south you are. For example, in Alaska, the length of the day is changing right now about 5-6 minutes per day, or about 40 minutes in one week! Imagine how that would feel, and it is a natural thing that happens every Spring and Fall. I think it is amazing how much the seasons impact the different geographies of the world, and a little understanding of the natural foundation for these effects is a nice thing to have.

A Must See: Four Planets and the Moon

This week the sky features four of the brightest planets in a beautiful lineup in the sunset sky. The illustration on the left, borrowed from Sky & Telescope Magazine, demonstrates how the planets all align themselves in a path across the sky known as the Ecliptic. This line in the sky, actually a gentle curve from west to east across the south part of the sky, is the plane of the Solar System as viewed from our observing platform on Earth. We see fast-moving Mercury close to the Sun, then Venus, Mars and Saturn, a most impressive line-up.

To set this into perspective, the young Moon emerges from the glare of the Sun on Tuesday 13th, moving somewhat parallel to the Ecliptic but each day a bit farther south of the Ecliptic. This is because the orbit of the Moon around the Earth is slightly inclined to the rest of the bodies in the Solar System. And as we just had a Total Solar Eclipse on Sunday, the Moon is following a path away from the Ecliptic into what is called the "descending node" south of the Ecliptic.

I will be talking about this at the California Academy of Sciences at their Nightlife event this Thursday in Golden Gate Park. If you are in or near San Francisco, please join me on the roof for Star Tours!

The Moon and the Ecliptic

Continuing from the last post, here's a snapshot of the Moon continuing on its journey across the morning sky, a series of guideposts to the Ecliptic. The view is what you would see around 5:30 am each morning here in San Francisco.

KFOG Podcast - Feb 12, 2010

I've been a frequent guest on KFOG 104.5-FM in San Francisco for the last two years. I am going to start a new series of programs with KFOG's Irish Greg that they will include in their Morning Show "Web Show" page. I am looking forward to regular recordings with KFOG, keeping the Fogheads up to date with the goings-on in the sky. Here's the first of our recordings with conversation about what to see in the Winter sky, a few words about the San Francisco Sidewalk Astronomers, and some tips for telescope shopping.

Leonid Meteor Shower 2009

The Leonids are reaching their peak tonight. This annual meteor shower peaks every time the Earth moves through the remnants of the comet Tempel-Tuttle. The meteor shower peaks when the Earth is directly intersecting the remnant streams ("filaments") from previous passes of the comet, and the peak for this year will be during the day of November 17th - unfortunate for those of us in the Western Hemisphere, but good for the night side of Earth at that time (primarily Asia).

Don't despair, however, as both the nights of Nov 16-17 and Nov 17-18 should provide some good meteor viewing even here in San Francisco. The Leonids appear to originate from the constellation Leo which rises in the east after midnight. As with all meteor showers, viewing gets better late at night into the early morning. Dress warmly and try to see a few. I'll be out early tomorrow to see what I can see.

International Space Station Marathon

When I host a star party or head outdoors in the evening, I like to check the status of satellites such as the Iridium communications satellites or the International Space Station (ISS). When they are visible, I like to point them out to friends. I marvel at these satellites in particular because they are (a) bright enough to see even with bright city lights, and (b) are well tracked and therefore predictable.

For the next few weeks the International Space Station will be particularly well positioned in its orbits around the Earth to be seen much more often than usual - even multiple times a day each week - throughout the month of July! I am looking forward to the graceful swing of the ISS across the sky, speeding at over 17,000 miles per hour overhead. NASA is calling this especially interesting period of time the Space Station Marathon and I think it will be great. Next week the Space Shuttle Endeavour will launch and link to the ISS to make the flyby even more interesting.

Here is the timetable for ISS visibility over San Francisco. If you don't live here, you can use the link on the right hand side of this blog to get to the general purpose ISS locator ("Space Station/Satellite Sighting").