The summer constellation Scorpius is now center-stage in the southern sky. It's always a treat to see the distinctive shape of Scorpius with red supergiant star Antares glowing in the sky. Through binoculars Scorpius is great because of an abundance of deep-sky objects in and near the constellation. And this week there is an extra treat as the moon passes through.
This Saturday is a chance to hear a great lecture and enjoy star gazing with the San Francisco Amateur Astronomers (SFAA) for their monthly star party on Mt. Tam. This month, Professor Lynn R. Cominsky of Sonoma State University is giving a lecture at 8:30 pm at the Mountain Theater. Her topic will include "blazing galaxies, intense stellar explosion and super-massive block holes" and should be quite captivating. Afterwards, the SFAA will set up telescopes for public viewing of the universe and there is a lot to see this time of year. The Moon will be a lovely crescent, Saturn is visible, and many deep space objects such as star clusters and nebulae will be on display. And if all goes well, I'll be there pointing out constellations with my trusty green laser pointer.
We all know what the Moon looks like when it is in its early phases, waxing from a thin crescent over a two-week interval of time through first quarter and then to full moon. Although many people might not be able to explain exactly which way the "horns" of a crescent moon are pointed, it's something that you just know is right when you see it. For us living in the Northern Hemisphere, the horns of the young crescent moon point left and up when you see the moon in the western sky after sunset. That is, they point primarily south (left) and up (east) because the moon is being illuminated by the setting sun -- which is typically to the lower right (northwest) of the crescent moon. If you suddenly saw the horns of the crescent moon pointing the other direction, you might find it strangely discomforting. I certainly would!
Each month as the moon wanes from full moon to last quarter to a thin crescent in the morning, the orientation of the crescent reverses compared to the first 14 days of the lunar cycle. But because these phases are visible late in the night and in the early morning, there are generally fewer opportunities to see the moon in these phases. When I am up late at night or very early before sunrise and I see an old moon in the sky, the reversal of the orientation of the horns always throws me off. This week and weekend if you are up late at night or early in the morning you can take note of this as the waning moon passes Jupiter (see image) and continues eastward in its path, slimming to a thin crescent by June 18-20. Sky and Telescope Magazine called the waning gibbous late at night an "eerie moon" and I can appreciate why they would call it that. Whenever you see the moon, be it a slender evening crescent just starting its 29-day cycle, or a bold full moon lighting up the night, or a waning gibbous, think about the view and how it makes you feel. If you can start to gain a familiarity with the phases of the moon, you will find it does indeed evoke different feelings depending upon which phase it is in.
It's been foggy in San Francisco. Really foggy. It seems like we have one clear night and six foggy nights per week lately and that is not what an Urban Astronomer likes. So it was with delight that I drove myself and my daughter to Mt. Tamalpais last Saturday for the monthly lecture and star party put on by the San Francisco Amateur Astronomers (SFAA). The Mt. Tam lecture series has been going on for many years and features a wide range of speakers from different areas of astronomy and cosmology. Following each month's lecture, the SFAA hosts a star party featuring a collection of telescopes, some homemade by SFAA members, pointing out the wonders of the night sky. Despite the foggy conditions in San Francisco and Marin, Mt. Tam is almost always a great vantage point because you are literally "above the fog" and despite the proximity to the city lights of the Bay Area, the viewing conditions on Mt. Tam are quite good. Last Saturday was no exception and the view of the first quarter Moon, Saturn and the spring and summer constellations was great. My daughter and I used an iPhone application called "Star Walk" to help us to identify the fainter stars in Libra and Virgo, to get a full picture of the big summer constellation Ophiuchus, and to even identify part of Centaurus. Using the "Star Walk" application we were able to see that the view from Mt. Tam toward the south was good enough for us to see the upper half of Centaurus and even though we could not see our nearest stellar neighbor, the Alpha Centauri system, we felt like we were nearly there. In fact, it was very interesting to see on my iPhone that the Southern Cross was only a few degrees below the horizon at that moment and even though we can never see it from 37 and 38 degrees north latitude (the Bay Area), I felt like I was *almost* there. I guess I need a vacation at a more southerly latitude ...
In 2005 I began writing a column for the San Francisco Waldorf School newsletter called "The Urban Astronomer." I started this blog in 2007 as a place to archive my articles and to offer additional insights on the night sky - even if you live in a big city. In 2008 I became an occasional guest on the KFOG Morning Show, and more recently on KALW and KGO. Archived shows are posted on the blog.