22 August 2014

KFOG Broadcast - August 12, 2014

I paid a visit to the KFOG Morning Show and had a fun chat with Renee about the Supermoon, Perseid Meteor Shower, How to Look At The Night Sky, and Star Parties in and around San Francisco. Click here to listen

14 August 2014

Jupiter & Venus Conjunction – Closest Approach Since 2000

After the Moon, the two brightest objects in the night sky are the planets Venus and Jupiter. Venus is a close neighbor and a very reflective planet, dominating morning and evening skies with its brilliant white shimmer against the changing colors of the dawn or dusk sky. Jupiter is the giant planet of the Solar System and despite its distance, is a bold and bright object for us to enjoy, especially in a telescope or binoculars.

Venus & Jupiter Conjunction
These two planets, like all of the objects in the Solar System, gradually change their position with respect to the background stars from day to day. All of the objects in the Solar System move along a common path across the sky, the Ecliptic. And from time to time these objects line up and create beautiful patterns and visually stunning sights.

On the morning of Monday August 18th (from North America), we will see Venus and Jupiter in a conjunction, a close alignment of the two bodies from our Earthbound point of view. The two will be in the east just before sunrise, so you’ll have to get up early to see this, but it will be rewarding. The two will be less than the Moon’s width apart, and given their bright nature, the pairing should be spectacular. Through binoculars, you will also be able to see a lovely star cluster, the Beehive Cluster, in the background of stars, as Jupiter and Venus will be in the constellation Cancer and passing through the Beehive.

The image (courtesy of Sky & Telescope) shows where to look. From San Francisco, sunrise will be at 6:30 am and the Venus-Jupiter pair will rise at 5:00 am, so you will need a good northeastern horizon to see the pairing, and the 30 minute window starting at 5:00 will provide the best dark-sky viewing conditions as the glare of dawn will start to interfere by 5:30.

You can find an excellent write up on the conjunction on Sky & Telescope's website. 

10 August 2014

Perseid Meteor Shower 2014 - what to expect

This year’s Perseid Meteor Shower will peak on August 11-12-13 and should offer up a moderately pleasing view of meteors but will be impacted by the nearly Full Moon. Meteors come in all sizes and shapes and during a reliable shower like the Perseids, you can see them all. However, moonlight increases the ambient lighting of the entire night sky and consequently makes the faint meteors all but invisible. The medium-strength meteors and the fireballs will shine through the glare of course, so the Perseids will have a showing, but just not at the rate we often see during a truly dark sky shower.

Perseid Meteor
I’ve often written that meteor showers are best viewed after midnight, when we are turned toward the path of Earth’s orbit (we are on the “front-face of Earth” after midnight), and we get better meteors. This still holds true, but in a recent article in Sky & Telescope, author Alan MacRobert suggests that early evening is a very good time to look for earth-grazers, meteors that enter the Earth’s atmosphere as a low angle and can be seen for much longer periods of time.  I will certainly be looking for these. I’m not an all-night observer and prefer looking out into the sky waiting for meteors when I am a bit more awake. So the idea of seeing grazers carries appeal for me in more ways than one. Last week on Mt. Tam we witnessed some spectacular meteors, one of which had a trajectory that suggested it was an early Perseid grazer.


For more information on the Perseids, check out these resources.

Image courtesy of Stefano De Rosa 

07 August 2014

August 2014 Supermoon

Moon at Apogee and Perigee
We are in the midst of a three-month period of Supermoons, a confluence of orbital nodes that brings us the Full Moon phase at the same time as Perigee, the closest approach of the Moon to the Earth. The next one is on August 10. The difference in the Moon's distance from the Earth from Perigee to Apogee is quite substantial, varying from 222,000 miles out to 253,000 miles, leading to the a 14% difference in the apparent size of the Moon. In addition, the Moon will be at the peak of the ascending node of its orbit, placing it somewhat higher in the sky than is typical for summer Full Moons.

There will be an earth-bound effect in the king tides that will result from the Supermoon and other factors. Here's my write-up about the impact on tides and the significant ebb tides we can expect this weekend.

Image courtesy of Wikipedia.

31 July 2014

August Opens With an Evening Show

Evening Show
The waning crescent Moon creates a majestic skyscape to open the month of August, shimmering against the dusk sky with the shiny colors of Spica, Mars and Saturn in the path. Each evening the trio of planets and stars will have the Moon in their midst, and the Moon will slip gradually eastward with each successive night.

I enjoy seeing the waxing Moon with its delicate shape and edge-on illumination from the Sun. It's fun to see in a telescope and it always holds the promise of the gentle glow of Earthshine. In the middle of summer, the ecliptic is low on the southern horizon and the Moon slices a gradual slope across the sky.

This view will be enhanced by binoculars, if you have them. You will see deeper into the details of the Moon and into the constellations along the southern horizon with the fringes of the Milky Way in view due south as darkness falls.

Image courtesy of Sky & Telescope.

30 July 2014

Sun and Moon and Ebb Tides

A kayaking friend of mine referred me to a question posed by a fellow kayaker regarding tides in and around the Golden Gate: Why are Ebb Tides strongest in SF Bay at night during the summer and during the day in winter? I love this kind of question, where the celestial mechanics of the Solar System impact the daily experiences of hobbyists and average people on Earth. 

First of all, why are there differences in size of high & low tides throughout the month and year? Each month the highest highs and lowest lows occur when the Moon is Full or New. That’s pretty simple. But there are two important factors regarding the Moon’s proximity to Earth on any given Full or New Moon. And there is one important factor regarding the Sun’s proximity to Earth on any given Full or New moon.

1. The Sun’s Changing Proximity

The Earth’s orbit around the Sun is elliptical, meaning that there is a close approach each year on January 4th (“perihelion”) and a corresponding far point in our orbit in July (“aphelion”). The New and Full Moon phases just before or after January 4th have higher high tides at the noontime tide, leading to a very fine ebb tide in the middle of the afternoon.

2. The Moon’s Changing Proximity

The Moon’s orbit around the Earth is elliptical, so there are times when the Moon is closer (“perigee”) and farther (“apogee”). Lately the press has made much to do about the “Super Moons” that occur when the Full Moon lines up with Perigee. On August 10, 2014 we will have a very fine Super Moon precisely at the same time as Perigee, so there will be higher high tides at midnight and lower low tides at dawn, leading to a very fine ebb tide in the middle of the night.

Another factor is the Moon’s location along its orbit from a north-and-south perspective. The Moon’s orbit around the Earth is inclined slightly and follows the “ecliptic” which also meanders above and below the plane of the equator, meaning that sometimes it is physically above the plane of Earth’s equator and sometimes below (“ascending and descending nodes” of the lunar orbit). If the Moon is above the plane of the equator, it is actually a bit closer to the land and water north of the equator, exerting a slightly greater tidal pull. The next peak of this effect is on August 9, 2014, so we can look forward to some amazing high and low tides at the next Super Moon. The ascending node and its impact are not tied directly to winter or summer, so this effect is less predictable.

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To answer the original question: there are good ebb tides each month at New and Full Moon, but the changing effects of perihelion and perigee cause the solar influence to be greater in Winter (hence the better daytime ebb tides) and the lunar influence to be greater in Summer (hence the better nighttime ebb tides).

This website offers additional insights into tides. 

Fun subject to think about! Wow!


20 July 2014

Binocular Astronomy

From an urban setting such as my home in San Francisco, I have a reasonable view of the night sky, knowing that from my own backyard I can see a good number of stars if I have clear skies and I am patient, allowing my eyes to dark adapt. In a city setting you are limited in the depth of the night sky you can experience by the ambient light in your exact setting, and the light pollution dispersed into the sky. But you can overcome these factors somewhat, by using binoculars.

Every time I am at a star party or astronomy gathering, in addition to a telescope I bring my binoculars. These are the fastest way to enhance your viewing whether you are in a dark sky or city setting. No matter what conditions you have, you will see deeper and will experience more richness in the night sky with binoculars. They are intuitive and require no special technical knowledge to use. You just point at a part of the sky and enjoy. Gary Seronik of Sky & Telescope publishes regular articles focused on binocular viewing and has an excellent resource book (I have a copy, of course) just for binocular viewing, Binocular Highlights. I highly recommend it.

Summer Milky Way in binoculars
During the summer months, point east and above to experience the richness of the Milky Way through binoculars. Even in city settings where the true outline of the Milky Way is not visible, binoculars will reveal some of that richness, exposing clusters and nebulae in the depths of the galaxy. I am particularly fond of the charts from the Great Smoky Mountain Astronomical Association for highlights in the summer galactic zone.

My old Celestron 10x50 binoculars have served me well for years and I carry them with me virtually everywhere I go. You should consider the same.

Image courtesy garyseronik.com.

14 July 2014

Mars and Spica Align

Mars and Spica Align
I've been watching Mars over the past few months as it slips steadily along the Ecliptic. It was near the bright star Spica several months ago as it was near opposition, then moved retrograde toward Porrima on the other side of the constellation Virgo, and now is back near Spica as it resumes prograde motion toward an August rendezvous with Saturn. The image shows where to spot the two bright objects in the south-west sky this week.

Image courtesy of Sky Safari.