During 2008 I have found myself captivated by close groupings of the inner planets (Mercury and Venus) with other planets and the Moon. This is a fortunate thing because just about every month there is something to look forward to. The next few days will bring about this happy circumstance as Mercury makes an evening appearance swinging by Jupiter, and Venus grows in brilliance in the sunset sky as it moves through Capricorn. The diagram shows some beautiful configurations that you can see in the coming days. The Moon will be near Venus on the 30th and 31st, closing out 2008 high in the southwest after sunset.
Circumpolar stars are those stars that are nearest the north star Polaris. These stars are in a special category because they are always visible every night and rather than rise in the east and set in the west like most of the stars in the sky (and the moon and planets), instead they circumscribe Polaris every 24 hours, hence the designation circumpolar.
From our latitude in San Francisco, 38 degrees north of the equator, we see Polaris 38 degrees up above the horizon due north. Although it is a celebrated star because of its unique location, Polaris is not the brightest star in the sky - that honor goes to Sirius in Canis Major. However, being at the point in the sky where Earth's north pole projects into space means that Polaris does not move over the course of a day or even over the course of a year, a truly unique star!
The "circumpolar region" of the sky is a circle that stretches from Polaris 38 degrees down to the horizon and 38 degrees in every other direction around it. Everything that you can see in this zone remain above the horizon every night. All the stars and constellations move in a counter-clockwise direction around Polaris, much as you might imagine a pinwheel that is anchored to a center point but the body of the wheel can spin in a circle. The same is true of the constellations that are within that 38 degree circle.
Today I was at the San Francisco Waldorf School talking with the sixth grade class about Circumpolar Stars and many other topics of interest for the young astronomer. The students in this class had been creating a number of illustrations of star patterns including the zodiac and the circumpolar stars. The illustration is taken from the workbook of one of the students (Sophia) and is a fine illustration of the circumpolar stars as seen this time of year shortly after sunset. Polaris is the star at the end of the handle of the Little Dipper and the other constellations show are all within the 38 degree circle around Polaris. As mentioned, over the course of 24 hours these stars will all move in a very large circle in a counter-clockwise direction. Thus in the early evening Cassiopeia is near the top of its path looking like an "M" but over the course of the night it will swing around to the left of Polaris eventually moving down low on the horizon by morning. In contrast to this, the Big Dipper is low on the horizon at nightfall but by early morning will have swept around to the right of Polaris and will be high in the sky at sunrise.
For those wishing for a more advanced lesson on circumpolar stars, you'll be interested to know that as you move north from San Francisco, Polaris appears higher in the sky and the circumpolar region becomes larger. What happens if you move south toward the equator? It's a fun thing to ponder.
Venus and Jupiter will have a conjunction at the beginning of the month of December. What is a conjunction? There are many uses of the term in astronomy, and here we use it to describe when two planets are very near to each other because they are on the same line of "longitude." I put the word longitude in quotes because in astronomy, we use a coordinate system similar to latitude and longitude, but the proper names are declination and right ascension. Therefore, when two planets have the same right ascension, we call that a conjunction.
The sketch (made by my daughter) depicts the sky as it will appear shortly after sunset on November 30th just as Jupiter and Venus are moving toward their closest approach. The scene will be made all the more beautiful by a young crescent moon just below the two planets. The next night, December 1st, the Moon will have moved just to the left and above the two planets. Both nights will be perfect for telescopic viewing, as the young Moon with its cratered surface (usually accompanied by earthshine) is always a beautiful sight, and you can see Venus at gibbous phase and Jupiter with its four bright moons. As mentioned in a previous post, these three objects with their special traits are three of Galileo's most famous discoveries with his telescope in the early seventeenth century.
This month offers a great opportunity to dig out that old telescope that you've rarely used and put it to work. Jupiter and Venus are putting on a show that will be of interest to anyone who has ever marveled at the heavens. These two planets are moving closer and closer and at the end of November will form a very compact grouping with the crescent Moon. What will you see?
Venus is brightening as it gradually moves closer to Earth in its orbit. Because it is nearer to the Sun than the Earth, it never climbs too high in the sky. For the rest of 2008 it is a brilliant evening "star", dominating the western horizon just after sunset. Jupiter, on the other hand, is much more distant from the Sun than the Earth and therefore over a year can be seen in all parts of the sky, moving gradually against the backdrop of stars but not nearly as quickly (from our Earth-bound perspective) as Venus. Jupiter has spent 2008 in the constellation Sagittarius and the diagram shows its present location, moving east of Sagittarius toward Capricorn.
Each evening for the next few weeks you will be able to see Jupiter and the background stars of Sagittarius gently drift toward the Sun while Venus holds its own. The combined effect is that Jupiter will move closer and closer to Venus. It is an experiment that requires nothing more than taking a moment each evening (or every couple days) to look west after sunset and note the relative position of these two bright objects. They are much brighter than anything else in the sky so you should not have any problem finding them. On November 17th Venus makes a very close encounter with one of the brighter stars in Sagittarius.
The evenings of November 30th and December 1st are particularly noteworthy as the young crescent Moon makes a close "fly-by" of the two planets, something that should be dazzling to see with a telescope or binoculars. Jupiter, of course, is impressive with its four bright moons, and Venus is always fascinating because it goes through phases just like our own Moon. By end of month, Venus will be a waning gibbous phase as it moves closer to Earth and slowly becomes a crescent over the next several weeks. Happy viewing!
Last year the US Congress made a change in daylight savings time. Rather than end in October it now carries into November. The effect of this is that mornings are dark in October, making it hard to get up and get going. On the other hand, it makes it much easier to see the morning sky and in the coming days it's going to be noteworthy.
Sunrise is happening this week at 7:30 which means that up until 6:45 or so, the sky is dark enough to see stars and planets. The diagram shows where to look for the Moon, Saturn and even Mercury. In the Fall, the path of the planets and Moon (the ecliptic) is in a very steep line from the point of sunrise into the eastern sky. Hence Mercury will be visible just above the point where the Sun will be rising, and Saturn and the Moon in increasing distances above and to the south of Mercury.
I love to see the very old Moon in the last days of its cycle. The ever thinning crescent reflects more and more "earthshine" and glows like a jewel in the morning sky. As October comes to a close, the waning Moon on the 24th, 25th, 26th and 27th should be a striking sight as the sky begins to glow with the dawn.
Nearly 400 years ago Galileo pointed a crude telescope toward the heavens and documented three remarkable things in the sky, discoveries that dramatically affected the understanding of the universe at that stage in history. With his telescope Galileo was able to see that the Moon was not a perfect circle, that Venus had phases, and that Jupiter had satellites of its own. Each of these posed a threat to the current body of knowledge of that era - Jupiter's moons and Venus' phases challenged the geocentric view of the universe and the non-perfect Moon challenged the Aristotelian theory of perfectly circular shapes in the universe.
With a simple telescope or even binoculars you can recreate some of these discoveries in the coming weeks and months. I'll write more about Venus in a future post. In October and November the phase of Venus will gradually transition from gibbous to half and later in the year to a crescent. The Moon is easy enough to study and is a marvel to view in any telescope or binoculars with the spectacular rocky edge of the surface always intriguing.
However, for the coming months Jupiter is the dominant "star" in the evening sky. Jupiter calls out for investigation because of the interesting texture of its surface and because of the changing position of its four largest moons. Called the Galilean satellites, these moons are visible to us even in low magnification and are interesting to observe because they change location so quickly -- even within the course of a few hours. They regularly pass through the shadow of Jupiter, yielding eclipses on a frequent basis.
From the nearest to the furthest moon, the names of the four satellites are Io, Europa, Ganymede and Callisto. Io is so close to Jupiter that it orbits the giant planet in less than two Earth days. Europa takes exactly twice as long and Ganymede twice as long again. Every few hours the overall pattern of these four moons is changed sufficiently to see new moons emerge from behind Jupiter, others disappear, and the overall pattern spread apart and then contract into a group.
Sky and Telescope Magazine has an excellent article on the moons and a very helpful pop-up screen that you can view in your web browser. It shows you the relative position of the moons of Jupiter at any time and can make a star gazing evening into a treasure hunt that will give you the feeling of discovery that will rival that of Galileo. So take the time to look to the south for the brightest object you can see (about halfway up the horizon above due south after sunset) and try it for yourself.
The California Academy of Sciences reopens in a beautiful new building on Saturday September 27th. This long-awaited opening will be a major event for San Francisco. The new building is an architectural achievement and a model of sustainability. I am particularly enthusiastic about the new Morrison Planetarium, one of the signature pieces of the CAS. I was able to preview it today in a press-only tour and I was very impressed.
There are several elements of a planetarium that make it distinctive. The newest planetariums (such as Morrison Planetarium here in San Francisco and Griffith Park Observatory in Los Angeles) feature state-of-the art projection systems that blend traditional star projections with high-resolution digital images, enabling a richer and more engaging presentation of astronomy. Morrison also features a tilted dome rather than an overhead dome, so you can fully experience the immersion of the screen without having to tilt your head back in your chair. The dome is tipped at approximately 30 degrees so you are viewing the show more like a movie theater than planetarium. The narration and sound are very good and the total effect is to truly transport you out of the day-to-day and take you untethered into space. It works!
The highlight of my visit today was the show in the Morrison Planetarium theater. The inaugural show is called Fragile Planet and it provides, through a series of stunning images - the Earth, the Solar System, nearby stars with planets, the Milky Way and other galaxies - a snapshot of the extremely delicate balance of conditions necessary to create life as we know it. What I found most interesting was the notion of the "habitable zone" that exists at just the right distance from the Sun (or around any star for that matter), the space in which planets can experience the temperature conditions as we do on Earth, conditions which support liquid water. During Fragile Planet you are transported to Gliese 581 d, an extrasolar planet orbiting a star in Libra. Gliese 581 d is a planet that due to its location near and in the habitable zone of its star, might support life.
All in all, the California Academy of Sciences is a superb place to learn about a broad range of sciences, housed in a magnificent facility that will be a treasure for San Francisco for generations to come.
Over the past many years I've made several visits to a biodynamic farm called Live Power Farm. The children at San Francisco Waldorf School have a tradition of going there to learn about farming and as a parent on several of these trips I have had a chance to get to know the farmers at Live Power Farm and the approach they embrace, biodynamic farming. It relates to astronomy because it is a very natural and harmonious approach to working with soil, seed, sun and the cycles of nature. As a member of the Live Power CSA, I share in the bounty of the farm and enjoy the amazing food they produce every week.
On my visits to Live Power Farm I learned that the farmers are very cognizant of the lunar cycles and planetary positions with respect to the Sun and Earth. They use a well known guidebook by Maria Thun and biodynamic calendars to guide their work on the farm and I was fascinated to see how farmers worldwide have come to understand cycles in the heavens and use these cycles in their farming. I spent many nights at Live Power Farm talking with the farmers and apprentices about the celestial mechanics of the sky to deepen their appreciation of how these cycles actually come to be.
Saturday September 6th I will be hosting a lecture with Stephen Decater of Live Power Farm. I will share my insights on how to understand the motions of the Moon and planets and how we see their motions from our vantage point here on Earth. Stephen will share his interpretations of these motions and how he works with the cycles in the heavens to guide his work on the farm. Please join us at 7:00 pm for the lecture and 8:30 for star gazing and telescope viewing of the skies. This event takes place at the Marin Waldorf School and is being sponsored by Live Power Farm, San Francisco Waldorf and Marin Waldorf Schools. I hope to see you there.
The evening sky in August and September will feature a terrific display of planets, stars and the moon in an elegant dance just above the horizon shortly after sunset. This interplay of planets is a chance to become familiar with the motions of the planets, particular the closest three (Mars, Venus and Mercury) in stark contrast with the motion of the stars and Saturn. Sky and Telescope has an impressive animation showing the motion of the objects in the evening sky from the start of August until the end of September. The stars move a small distance closer to the horizon every evening of the year, but the planets move from the west toward the east in their orbit around the sun.
While observing in the mountains two weeks ago I saw several meteors streak across the sky. Meteors are always a joy to watch because they appear completely without warning yet are so brilliant to see. Seeing one is the reward for keeping focused on the sky and keeping your eyes open and attentive. Every night of the year there are many meteors to be seen but throughout the year there are particularly intense periods of meteor activity called Meteor Showers. The biggest show of the year is the Perseids Meteor Shower which peaks this year during the morning of August 12th. StarDate Online has a helpful list of meteor showers throughout the year and provides some insight how they happen.
There are two simple guidelines for observing the Perseids. First of all you want to be in a dark location with a clear view of the eastern sky. From San Francisco there is a great deal of light pollution which will obscure many of the meteors. The brightest meteors will still be visible but the rate will be considerably lower than the 1-meteor-per-minute rate you would see in very dark skies. So if you want a good view, drive east away from urban centers. Second of all, you want to view them in the early morning hours when the earth is speeding into the spacedust that makes up the meteor shower and when the moon has set. The best viewing should be from 2 AM until 4:30 AM. NASA has a helpful page showing where to look in the sky. During the early morning hours the rate will increase up to a maximum of 1 per minute.
The total solar eclipse of August 1st was well documented. Sky and Telescope has a nice gallery of pictures. I find that photos can't really do justice to the real thing, but a collection of photos like those on Sky and Telescope are interesting if taken in total -- that is, look at many of them and imagine seeing all of these images at the same time with your eye. That is what it is like at an eclipse. Your eye can see a lot more shades of brightness than a camera and besides the visual spectacle of an eclipse, being there is an unforgettable experience.
A colleague showed me this amazing view of the total solar eclipse from an airplane. The most intriguing thing to me is the way the shadow of the moon looks from the vantage point of an airplane and how it moves from north to south during the very short period of totality. It must be a very eerie sight to see in person.
Astrophotographer Dennis diCicco takes excellent photographs and this depicts him at work in China.This image gives you a sense of what it looks like to be there with a dusk-like but not dark sky. You can see Mercury and Venus to the upper left of the sun-moon pair.
Friday August 1st is the date of the next Total Solar Eclipse. Like lunar eclipses, solar eclipses happen frequently but total solar eclipses are somewhat less common and furthermore, to see a total solar eclipse you generally have to travel to a narrow track (unlike Lunar Eclipses which are visible from just about anywhere on the night side of the earth).
The eclipse this week follows a very narrow track across the arctic regions of the globe and finishes across Siberia and western China. The Exploratorium of San Francisco is sending a crew to report on the eclipse including a live video linkup and webcast from the ground in China. For the hard core eclipse fans who want to feel some of the excitement without leaving the Bay Area, the Exploratorium is having an all night party. The Exploratorium did this for the last total solar eclipse in Turkey (both broadcasting live from Turkey and having a party at the Exploratorium). I had the good fortune to travel to Turkey and witness that solar eclipse from Side on the Mediterranean coast.
Given that the eclipse happens during the afternoon in China, it will be very early Friday morning here in California (4 am). For those who want to watch it live on the internet, you will have to get up early. And for those who are into long-range planning, the next Total Solar Eclipse is in July 2009 in Asia and the Pacific, and in 2017 in the United States.
I spent last week at the Stanford Sierra Camp at Fallen Leaf Lake near Lake Tahoe. At nearly 6400 feet elevation with dry clear skies, the view of the night sky was excellent. I hosted two stargazing sessions during the week in which fellow campers took in the view of deep space objects such as the Lagoon Nebula, Swan Nebula and Andromeda Galaxy plus some riveting views of Jupiter's most prominent cloud belts and the four Galilean Moons. All of this was possible using a 5 inch telescope under the right conditions. The view from the boat dock at Sierra Camp faces east, motivating me to get better acquainted with a few constellations I had never fully appreciated such as Andromeda, Pegasus, Delphinus, Aquarius and even Aquila, because many of the stars in these constellations are not visible in the city. The dark skies gave me a chance to see them in their entirety. It's never too late to see something new so if you get out in the dark this summer, take a star chart and make a few discoveries.
Growing up in Los Angeles I saw summer concerts at the Hollywood Bowl and noticed that even in the bright lights of LA, you can see the Summer Triangle shining above the stage at the Hollywood Bowl. That perspective never has escaped me and whenever I see the Summer Triangle during July or August in the early evening, I can visualize myself looking at the stage at a Hollywood Bowl concert. Last night I was watching Steely Dan at the Berkeley Greek Theater and learned a new view, that of the stars over the Berkeley Greek at night. Above the stage to the left was Scorpio, rising higher as the concert went on. To the right were the stars of Leo (with Mars and Saturn still nearby in the glowing sky after sunset). Just above the stage is Spica (the brightest star in Virgo) and Arcturus (the brightest star in Bootes). Most of the other stars in Virgo and in nearby Libra are too washed out by city light and moisture in the air to be seen above the Greek theater stage, but there were still plenty of bright stars and planets to enjoy. Later in the evening Jupiter, now visible in Sagittarius, rose in the east (above the stage to the left) and dominated the sky. I enjoyed getting to know a new night sky above a popular venue and look forward to the memories of that concert every time I see this particular lineup of stars.
The evening sky has been graced by the sight of Saturn and Mars over the previous months and as the two slowly fade into the glare of sunset they are making one last beautiful show with the Moon and with each other. On July 5th and 6th Mars and Saturn create a beautiful group next to the crescent Moon and they slowly move closer to each other until Thursday July 10th when they are separated by a mere 0.7 degrees, slightly more than width of a full Moon. Mars, being much closer to Earth than Saturn, appears to move a small amount to the east each evening and has been gradually drawing closer to Saturn. It's quite a finale to see these two worlds so close to each other from our point of view. By month's end they will be nearly out of sight.
Three major planets are well placed for viewing. This chart of Jupiter and the Moon and Sagittarius shows the changing view of the trio as the Moon moves across the sky the evenings of June 18 and 19. Jupiter and Sagittarius will remain in close proximity over the summer with Jupiter being the brightest beacon in the sky each night. Over the summer Jupiter will gradually become visible earlier and earlier in the evening. Saturn and Mars are slowly slipping into the evening glare but remain visible for a short while after sunset. Within the next month they will entirely fade from view, so catch a glimpse and enjoy the show of these two wanderers in the midst of Leo the Lion.
As I write this entry, I am in Melbourne, Australia on a business trip. Melbourne is approximately 38 degrees south of the equator and I have always likened this to San Francisco which is approximately 38 degrees north of the equator. I think of these two coastal cities having similar climate and similar sky conditions but in exactly the opposite way. Being 38 degrees north of the equator San Francisco is heading toward the summer solstice. The days are getting longer and the sky, as always, appears to pivot around the north star which is (by no coincidence) 38 degrees above the northern horizon, with the Sun and planets moving in a long arc across the southern half of the sky.
Melbourne presents a mirror image of the sky in many ways. The Sun does in fact still rise in the east and set in the west, but the Sun and planets move in a long arc across the *northern* part of the sky. The days here are short and getting shorter and Australia and other southern hemisphere countries prepare for the onset of winter in a few weeks. The mirror image of the sky in the northern hemisphere is visible in that the sky appears to pivot around the southern point of the sky. There is no bright star near the southern point of the sky so we don't have exactly the same scenario (ie. no south polar star like Polaris in the northern hemisphere), but the motions are similar -- in the opposite direction.
For example, in the northern hemisphere the Big Dipper moves around the north star in a large sweeping circle in a counter-clockwise direction, but in the southern hemisphere the southern constellations pivot around the south "pole" in a large *clockwise* circle every 24 hours. The Big Dipper and other star patterns and constellations near the north star are visible all night in the northern hemisphere and are called circumpolar stars, but are not at all visible from my location here in the southern hemisphere. Similarly, the circumpolar stars in the southern sky are not visible at all from San Francisco. Hence we never see the Southern Cross or Alpha Centauri (one of the nearest stars to Earth) or the Magellanic Clouds (nearby galaxies) from the northern hemisphere.
The early travelers setting sail across the seas and around the globe noted these changes in the sky and learned some valuable rules about celestial navigation. Although we don't depend upon these markers to tell us where we are on the globe anymore, I enjoy looking out for these changes in motion in the sky as I travel from time to time far north of San Francisco or in this case far south. The Southern Cross is a beautiful sight from here, even though the sky has been too overcast to see much else.
As Saturn continues to dominate the evening sky, Jupiter now rules the morning sky. It shines brightly in the pre-dawn sky near the constellation Sagittarius. This week the Moon will pay a visit to the scene, passing through the "teapot" of Sagittarius on May 23rd and near Jupiter on May 24th.
When you look toward Sagittarius you are looking nearly at the center of the Milky Way Galaxy. While the Moon is passing through, you can't see much of the Milky Way at all, but once it has moved on and the light of the Moon doesn't impact the sky, you will have a better view of the center of our galaxy. Use binoculars and peer into Sagittarius and you will see a wealth of beauty, even with city lights. And if you don't want to get up so early in the morning for the view, wait until Summer and Sagittarius will be rising earlier and earlier in the night.
The days are getting longer as the Earth moves in its path around the Sun. Why do the days change in length? This has to do with the axis of the Earth being tipped. Why does that affect the length of a day?
For illustration, visualize of a globe mounted on a base. Globes are always mounted at an angle, representing the fact that the Earth is tipped 23.5 degrees from vertical. That is, as the Earth spins on its axis every 24 hours, the line around which it spins points up and we call that direction North. This point in the sky is fixed over a period of hundreds of years and changes very slowly such that in a lifetime, the axis of the Earth will point nearly perfectly toward a single point in the sky. It is pure coincidence that for us in the current era, this point in the sky is almost directly where the North Star can be found. This star, Polaris, is the current north star but in a few thousand years won't be. If you want to learn more about the changing location of the pole star, you will want to read this article on "precession of the equinoxes."
As the Earth travels on its 365-day journey around the Sun, the axis of the Earth remains fixed in the same direction, North. That means that for half of the year the north side of the Earth is tipped toward the Sun, and for the next half of the year the south side of the Earth is tipped toward the Sun. That leads to the seasonal change that we all come to understand. When the north side of the Earth is tipped toward the Sun, we get more hours of light each day in the northern hemisphere. We are in that situation right now and with each passing day between now and the Summer Solstice, the days become longer. A side effect of this is that the Sun appears to rise north of due east and set north of due west. As the Sun moves across the southern sky, it climbs higher with each successive day. In the San Francisco Bay Area, it will be nearly in the zenith on the day of the Summer Solstice. This diagram illustrates how the light changes on the Earth throughout the year. Enjoy the sunshine and warm weather and take note of how high the Sun climbs in the sky at midday.
Note: Mercury remains visible for a few more days and is changing phase rapidly. It is found in the north-west part of the sky just after sunset.
The western sky just after sunset is exploding with beauty and it is well worth the time to spend a few minutes soaking it in. Right now there are three planets on display in the evening sky along with the fine winter constellations still visible as the glow of dusk fades. I have been watching this over successive evenings and am impressed with the variety of colors and patterns visible after sunset. This week the sun drops below the horizon around 8:00 PM pacific daylight time and the sky is reasonably dark by 8:30, but by 9:00 the best viewing emerges.
First up is the fast-moving planet Mercury which will spend the next few weeks making a strong showing in the western sky. Because it is so close to the sun it never moves far above the horizon, but we will be seeing it at one of the best views of the year. This diagram shows Mercury in a close encounter with the Pleiades on May 1st, but it will continue to hover in the west through mid-month. It is bright enough to be seen in the glare of the dusk sky and you will see it best if you have a clear western horizon.
Next is Mars which continues to share the limelight with the twin stars of Gemini, Castor and Pollux. Mars is distinctive in comparison to the Twins because of its deep orange color. It is slowly diminishing in brightness but is still bright enough to be easy to find.
Saturn is the highlight of the planetary lineup, high in the sky after sunset in the constellation of Leo. More on Saturn can be found in my last post.
The bright constellation Orion is now setting in the glare of sunset, slowly fading from view as the constellations of summer arrive in the east and begin their reign. Nonetheless, a very bright grouping is still visible in the western sky featuring three stars from three different constellations. A distinctive grouping of stars from different constellations is known as an "asterism" and the Winter Triangle is one of the more distinctive asterisms in the sky. It contains Sirius, the brightest star in the sky which is in the constellation Canis Major, Procyon, the brightest star in Canis Minor, and Betelgeuse, which is in the constellation Orion. This diagram provides a helpful guide to this pattern. Each of these stars have distinctive colors, with Betelgeuse an orange-red (it is a red giant star), Sirius whitish-blue, and Procyon in-between the two as a plain white star. Enjoy the sky this spring - it's full of remarkable things to see.
This Spring there are two bright planets in the evening sky that you should stop and see when the weather permits. The first is Saturn, the second is Mars.
Saturn is well placed for viewing in the evening and is high in the sky after sunset. Saturn is currently spending several months in the constellation Leo and Saturn itself is near the bright bluish star Regulus which is the brightest star in Leo. They are nearly directly overhead in the evening, slightly to the south. Saturn and its famous ring system are very large compared to all the other planets and therefore reflect a lot of sunlight back to Earth. Saturn is a fairly colorless planet despite what you see in photographs which are often color enhanced. In natural light, Saturn is a blend of off-white, yellow and grey hues and therefore from our point of view looks like a medium-bright yellow-white star.
As Saturn travels in its 29 year path around the Sun, the ring system is more tilted toward Earth for a period of time and then less tilted toward Earth at other times. Sometimes we see the ring system edge-on and because it is so thin, it is very difficult to see the rings at all. For this reason, Saturn is sometime brighter and sometimes dimmer. Right now it is going through a brighter phase and with binoculars stands out as something other than a star. Find a comfortable spot (or lie on a blanket) and spend a few moments looking up near the highest point in the sky. In binoculars, Saturn looks like an oval, brighter than the surrounding stars and shaped differently than everything around it.
Mars is also well placed for viewing in the evening and is in the western sky after sunset. Mars is currently spending time in the constellation Gemini near the twin stars of Castor and Pollux. This diagram shows where to locate it later this week when the Moon passes near it on April 11th. Mars is one of the closest neighbors to Earth and when the alignment is right, can be quite bright. However, at this point it and the Earth are moving further apart and as such, it's brightness is fading from week to week. It still stands out among the stars, and of course it is a distinctive color of orange so it is easy to spot. But unless you know where to look, you might not realize it is a planet and instead think it is just another star. So use the Moon as your guide this week and take it in.
The Space Shuttle launched this morning and will be orbiting Earth for the next few weeks. While orbiting, it will be docked with the International Space Station from the 12th to the 24th. The two will be visible on a regular basis for brief periods just before sunrise or just after sunset. Look here for details of visibility from San Francisco. You can also check visibility for any location on Earth.
I've been asked in the past how to find Mercury. Because it is so close to the Sun compared to any other planet in the Solar System, it is harder to spot than the rest and never appears very far away from the Sun (that is, it never appears high up in the night sky). However, because it is relatively close to Earth, it can also become quite bright. These two factors combine to make Mercury a challenge to see but still a fun goal for many. The coming weeks offer an opportunity to try to see it.
Mercury and Venus are both circling the Sun inside the orbit of Earth and both move faster than Earth. In a single 12 month period of time, Mercury will circle the Sun over 4 times. As it speeds on its orbit, it is visible low on the horizon in the evening or morning sky. Right now both Mercury and Venus are very low on the horizon in the morning and if you have a clear view and good timing, you can see the two dance along the horizon. The diagram shows where to look for them.
In 2004 NASA launched the Messenger spacecraft to explore Mercury and in January 2008 it finally made its first pass, flying just over 100 miles above the surface of Mercury. Messenger is returning some amazing photographs of the planet. To my surprise, Mercury looks exceedingly similar to our own Moon. For pictures, visit http://www.nasa.gov/mission_pages/messenger/main/index.html.
Mercury and our Moon have much in common, being of similar age, made of similar minerals, and both having no atmosphere*, they are bombarded by meteors and have no erosion or surface flows which change its appearance over time. Hence they both appear similar on their surfaces. For me, seeing the photos reminds me that there are lots of things we share in common with our neighbors in space and by exploring our own Solar System we can better understand what is happening in other star systems and galaxies.
* Note: Mercury has an extremely thin atmosphere due to the solar wind lifting particles off the surface of the planet, but this layer of atoms is being constantly "burned off" and is not a permanent atmosphere as we have on Venus, Earth or Mars.
Mark your calendar for Wednesday February 20. Weather permitting, we will experience a total eclipse of the moon, one of the best timed eclipses in years and the last total lunar eclipse until December 2010. This one is timed well because it will be underway at sunset and will be at its peak during the 7:00 pm hour, much easier to see than the eclipse last August which took place in the middle of the night in San Francisco.
A total lunar eclipse is a beautiful showcase of many astronomical phenomena. Lunar eclipses were used by scientists hundreds of years ago to prove that the Earth is round because the darkening of the Moon is actually being caused by the curved shadow of the Earth. The early and late phases of a lunar eclipse are punctuated by the curved shadow of the Earth moving across the otherwise full Moon. These phases take a little over an hour to happen and as the Moon glides deeper into Earth's shadow, the illuminated surface of the Moon becomes less and less.
During the period of "totality" all direct sunlight is obscured by the Earth and the Moon fades into a dark disk, a rather stunning image to behold. Every total lunar eclipse has a different appearance because a small amount of sunlight is refracted by the atmosphere of the Earth and illuminates the otherwise-darkened surface of the Moon. The same effect that causes the sky to turn red, orange or pink at sunset is responsible for the color that you see on the Moon. Think of the light as the collective light of all the sunrises and sunsets around the entire globe. Since no direct sunlight is reaching the surface of the Moon during totality, anything we see will have been first refracted by the Earth's atmosphere, then it will have traveled 240,000 miles to the moon, and then will reflect back from the Moon to the Earth for us to enjoy!
If the Moon is very dark during the eclipse, you should be able to spot two bright objects on either side of the Moon. These are the bright star Regulus in the constellation Leo, and the planet Saturn. The entire grouping should fit nicely in the field of view of binoculars so get out whatever you have, dust it off, and pull up a chair. The totality phase of the eclipse will be from 7:00 until 7:52 pm.
By watching the eclipse from start to finish you can get a very good feel for just how far and fast the Moon moves in its orbit around the Earth. When the Sun sets on the evening of the 20th, the Moon will rise due east and quickly move across the southern half of the sky. This motion is due to the rotation of the Earth on its axis. However, the darkening of the Moon as it moves through the shadow of the Earth is due to the orbiting of the Moon around the Earth, something which is slower and thus more subtle. By watching the changing position of the Moon against Regulus and Saturn, you will be able to get a sense how far it moves against the background stars in a short span of time.
Sometimes the stars do in fact align and all is well. OK, perhaps not the stars but the planets, and suddenly they shine in the sky as the clouds and rain in San Francisco have miraculously disappeared just in time. The morning of Friday February 1st is one of those special moments when the brightest objects in the sky line up and make for great viewing. As Venus graces the morning skyline, it is being joined by Jupiter which is rising each morning higher out of the morning glare of sunrise. They pass very near to each other on the morning of the 1st and are about a half degree apart - that's about one full moon's width. But the moon is not far off, a crescent just up and to the right next to the bright star Antares in Scorpio.
The next few weeks will offer the chance to see the change in the lineup, as Jupiter continues to climb each day in the morning sky while Venus stays low on the horizon. That is because Jupiter, being considerably further away from the earth, moves at more the same pace across the sky as the sun, whereas Venus, being much closer, actually is speeding around the Sun and stays lower on the horizon.
This week the waxing moon journeys across Taurus and Gemini. As it does, it encounters the Pleiades, the small but distinctive cluster of stars in Taurus also known as "the Seven Sisters." On the evening of January 17th, the moon will graze through this region of the sky in what is called an "occultation" of the Pleiades. Occultations are special times when a celestial object is "blocked" from our point of view by another object. The most common are occultations of stars and planets by the moon. When this is being caused by the moon, it affords anyone with binoculars or a telescope to easily observe the motion of the moon against the background stars as the moon makes its monthly journey around the earth. On the evening of January 17th as the moon variously covers and uncovers stars in the Pleiades, you will be able to sense that motion. Over the course of approximately three hours the moon will move across the Pleiades.
Two days later, the nearly full moon will pass very close to Mars but will not occult the planet from our vantage point in San Francisco. Observers much further north (in Canada) will in fact see the moon completely cover Mars. Because Mars is bright and fairly close to earth right now, the sight of it so close to the full moon will be quite beautiful. Take a few moments on the evening of January 19th to enjoy this spectacle. I observed a similar lineup of moon and Mars in December during the previous full moon two days before Christmas.
Earlier this month I was a guest on the KFOG radio morning show (104.5 FM in San Francisco). KFOG features the best morning show program in the San Francisco Bay Area (in my humble opinion) because the DJ and his crew talk about relevant subjects and current news items in an intelligent way. I thought it would be interesting for the KFOG listeners, affectionately known as Fogheads, to hear about astronomy and I asked to be a guest on the program. Morning show producer Greg McQuaid welcomed me to join and on January 8th I was a guest. The program went well and the Fogheads asked interesting questions. I am invited to return to the morning show in March and will post an update to the blog when the date is confirmed.
There were many more questions from Fogheads that we did not get to answer during the show, so I will post them to this blog from time to time.
Eclipses: the authority on all things related to eclipses: Fred Espenak's NASA site Good for listening: StarDate is a quick daily dose of very general astronomy topics. Astronomy Cast is an excellent weekly podcast for those looking for deeper insights.
Sun and Sky Conditions: The Clear Sky Clock provides a wealth of detail on sky conditions with details on transparency, darkness, seeing, and so on. The US Naval Observatory provides exact sunrise and sunset times anywhere on the globe.
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.