Moon Traveling Along the Ecliptic

The Moon, like the planets and the Sun, travels along a special path in the sky called the ecliptic. Observationally, the path arcs generally across the southern half the sky from west to east, but it is not a simple arc that is in the exact same part of the sky year round. Rather, it curves higher in the sky and lower in the sky as the seasons change.

Right now, in late winter, the Sun remains low in the sky but is gradually climbing the ecliptic, getting slightly higher each day. The Moon this week is just past full, and therefore is traveling along the opposite side of the ecliptic in a part of the sky where the ecliptic follows a low arc in the sky from west to east. And because the Moon takes 29 days to circle the Earth once, and the Sun appears to take 365 days to "circle" the Earth once, we can observe the Moon's motion along the ecliptic much more readily than the Sun's. The image helps to visualize this over the course of four days in which the position of the Moon at the same time in the dawn (an hour before sunrise, about 5:30 to 5:45 am this week in San Francisco) traces out the low, sloping arc of the ecliptic -- and slices close to Saturn as well.

The Urban Astronomer speaks!

I want to let Bay Area readers know about a very exciting event coming up on Tuesday March 2nd in San Francisco. The event, Ignite Bay Area, is one of a collection of global "Ignite" events happening next week. If you have never experienced an Ignite presentation, they are very fast and focused 5-minute talks about everything from geek technology to social trends to .... astronomy! I'll be presenting a talk on amateur astronomy that I trust will inspire and motivate many to look up in the night sky and make a cosmic connection. Hope to see you there!

Winter Sky Show: Gemini, Mars and the Moon

Gemini is one of the finest constellations you can see during the winter months, easy to spot because it traverses the highest spot in the sky (the zenith) and features two bright stars, the twins Castor and Pollux. These two stars are well known because they symbolize the heads of the mythical twins. The stars that make up the rest of the bodies of the twins are less bright and require slightly darker conditions than we will have this week, but I provide an image nonetheless so you can see the rest of the stars when conditions permit.

Mars is the bright orange beacon of light that is gracing the night sky, the brightest object high in the sky for the next many weeks. As Mars orbits the Sun, we observe it moving against the backdrop of the Zodiac constellations, changing its position gradually from month to month as it travels eastward from our Earthbound perspective (this is called prograde motion, in contract to retrograde motion – more on that in a future post). It is about to start moving away from the twins of Gemini through Cancer toward Leo the Lion where it will arrive in May.

The Moon sweeps through this busy part of the sky, passing slightly south of Gemini, Mars and later this week the bright star Regulus in the constellation Leo. The bright Moon will drown out the background stars of these otherwise bright constellations, but the prominent stars Castor, Pollux and Regulus, along with Mars, will shine beside the waxing gibbous Moon. Binoculars or a telescope are a good idea if you want to see this close up!

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.

Old Moon, Young Moon

Every 29 1/2 days the Moon completes one cycle in its orbit around the Earth. For the last few days of the cycle we have an "old moon" and then just after New Moon we have the opportunity to see a very "young moon." I love the challenge of locating the very thin crescent Moon on the horizon, but when found, the reward is worth it, because the Moon always looks a jewel in the sky.

This week we've had a few opportunities to see the very old moon passing by Mercury in the dawn glare. After the New Moon on Saturday, find a good western horizon and try to locate the very young Moon in the glow of dusk. On Sunday 14th it will pass just next to Jupiter and Venus, extremely low on the horizon. You will want to have binoculars nearby to enhance the view. On Monday the Moon is higher in the west, and by Tuesday it is an easy target in the sunset sky. Well below the Moon on Tuesday, however, Jupiter and Venus have their closest approach for quite a while, being about 1/ 2 degree apart (a moon width). For this, you will want binoculars because the two planets will be just on the horizon after sunset.

Get Involved: Cal Academy, Star Parties, meet John Dobson

February is a busy month here in San Francisco for those who are ready to take a step forward and get involved in a local astronomy event or two. Here's the lineup.

On February 11, the San Francisco Amateur Astronomers (SFAA) team up with the California Academy of Sciences for a new series of astronomy talks and star tours on the Living Roof of the Cal Academy. I'll be giving the talk this Thursday during the NightLife event at 7:15 pm. More information and tickets on the NightLife webpage.

On February 17, the SFAA holds its monthly meeting and lecture at the Randall Museum in San Francisco. And on February 20th they have their City Star Party and Telescope Workshop. You can dust off your old telescope and bring it out for a quick lesson on using your telescope (before the sun sets), and then enjoy stargazing at the City Star Party. This is at Lands End in San Francisco.

On February 25th and 26th, the amateur astronomy community of San Francisco bids farewell to a living legend in the field, John Dobson. John is a co-founder of the San Francisco Sidewalk Astronomers (they call what they do "urban guerilla astronomy") and the creator of the easy-to-build and easy-to-use telescopes that bear his name, Dobsonians. There will be a get together with John on Thursday 25th in the Sunset District of San Francisco, and sidewalk astronomy with John at a location to be determined in the city, to say Farewell as John moves from San Francisco to Los Angeles. I am impressed with Sidewalk Astronomers and especially with John Dobson, who had a singular vision to make telescopes accessible to anyone who wants to build one out of inexpensive parts, and to get these telescopes out on the street so everyone can appreciate the wonders of the sky and see something they hadn't seen before. I respect that.

I hope to see you at one of these events.

Annular Solar Eclipse of 2010

Eclipses are very exciting events, special moments that provide beautiful visual spectacles in the sky. Every year there are typically two to three eclipses of the Sun ("solar eclipses") and two to three eclipses of the Moon ("lunar eclipses"). And for each eclipse the event can be "total" (where the Sun or Moon is fully blocked out), or "partial" where a portion of the Sun or Moon is blocked out, but a portion is still visible.

Last month there was one such event, a type of solar eclipse called an Annular Eclipse. In this configuration, the Moon's disk appears to block out most the Sun but does not completely block it out. What makes the Annular Eclipse very special, however, is that the disk of the Moon is fully encircled by the Sun. The eclipse in January was not visible here in San Francisco but was seen in the eastern hemisphere. A fellow astronomy blogger and resident of Sri Lanka, Desh, put together an eclipse page that has video footage of the event and lots of great photographs. He organized a major eclipse viewing event for Sri Lanka.

Throughout 2010 there are more eclipses. The biggest event of the year is the Total Solar Eclipse that happens this July 11th, but again will not be visible here in San Francisco. To see this one you will need to travel to the South Pacific. The NASA Eclipse web site is full of details on this and every eclipse and for those of you who want to travel to see a Total Solar Eclipse someday, consult the NASA Total Solar Eclipse Paths map on their website. I think of it as a long-range travel planner!

For those of us in the Bay Area (and the entire Western Hemisphere), mark your calendars for December 21st when we get a beautiful Total Lunar Eclipse on the solstice to welcome in the winter.

Note: for a nice audio description of an eclipse, listen to my recent interview on KALW (just after the stargazing part of the interview).

Leo the Lion

Leo is one of the twelve zodiac constellations, the name "zodiac" sharing its origin with the word "zoo" -- appropriate for the ring of mythical animals found in the sky. Leo is a very easy-to-locate constellation because it has one very bright star (Regulus) and quite a few moderately bright stars in a distinctive pattern that resembles a lion. The image at left shows the general outline of the stars in Leo, with the sickle (or backwards question mark) at the head of the lion, something that is easily identifiable as Leo rises in the east in the winter. For the coming months, it will be appearing higher in the east and traversing nearly overhead throughout the evening.

Because they form a band around the sky that follows the Sun's path, each of the zodiac constellations has frequent visitors as they grace the night sky, from the Moon to the planets. Leo has been the home of Saturn for the last three years, but now Saturn is drifting slowly eastward into Virgo. On the west side of Leo is Mars, currently in retrograde in Gemini, but soon to be speeding toward Leo and a close encounter with the bright star Regulus in June.

Take some time to become acquainted with this celestial Lion, and you'll know how to quickly navigate to Saturn and Mars throughout the spring and into the summer.