06 November 2019

Transit of Mercury on November 11, 2019 - don't miss it !

On Monday November 11 we will have a chance to witness a very unique and special event, a transit of the planet Mercury across the face of our Sun. This is a rare event, happening only 13 times in a century. The next one won't take place until 2032.

What is a transit? It is a precise alignment of the Sun, Earth and another celestial body. In this case, that body is Mercury, the closest planet to the Sun and a fairly small planet. It orbits the Sun every 88 days, and when we have this special alignment with a transit, we are witnessing the proper motion of the planet as it progresses in its orbit around the Sun. Mercury's diameter is 194 times smaller than the Sun so it will in fact appear as a tiny, perfectly round black dot against the surface of the Sun (the Photosphere) and will take approximately 5 1/2 hours to cross from solar limb to solar limb.
Time Lapse of Mercury Transit in 2016

If you want to see this, you will need special equipment that incorporates the correct level of filtering to reduce the Sun's intensity to a safe level, and magnification to make it possible to see the shape of Mercury against the disk of the Sun. Many astronomy clubs and public observatories will host viewing events. Here in Munich, the Volkssternwarte M√ľnchen will be open for the entire duration that the transit is visible from here, starting at 1:35 pm and continuing through sunset which is at 4:39 pm on Monday. We just need clear skies and a proper filter and we can enjoy this unique and rare event.

For general information about the transit and more detailed timing for US-based locations, check out this article from Space.com.

Warning: do not stare directly at the Sun for any length of time, and in particular do not look at the Sun through a telescope or binoculars with "eclipse glasses" as these will not protect your eyes sufficiently. Only observe the Sun directly with a high quality solar filter built especially for a telescope or binoculars.

Image courtesy of NASA.

14 October 2019

Cygnus and the Milky Way

Autumn brings us cooler evenings and earlier sunsets, but it’s not yet too uncomfortable to go outside and gaze up into the heavens for a look at our own galaxy, the Milky Way. The best way to enjoy this from a city setting is to get out to a place where you can lie flat on your back (on a blanket or lounge chair) and look directly overhead. In the evening the constellation Cygnus dominates the sky and is easy to find even with light pollution around you. Cygnus is also known as the Swan, as it resembles a giant swan flying gently toward the north-east and is also known as the Northern Cross, since its brightest stars outline a cross quite clearly. The brightest star of Cygnus is Deneb, a beautiful blue giant star that is one member of the Summer Triangle, an asterism that is made up of three of the brightest stars in the summer and fall skies. The diagram below shows the region of the sky directly overhead (zenith) with the three bright Summer Triangle stars identified in white, and the cross shape of Cygnus in purple.

Cygnus the Swan, or Northern Cross
Cygnus is directly in the band of stars of the Milky Way that we can see across the night sky. In dark conditions, the band of the Milky Way glows like a faint cloud but in the city that is unfortunately lost to light pollution. However, if you have binoculars or a telescope you can still enjoy the richness of the Milky Way by looking deeply into Cygnus where you will find many treasures that are quite accessible. I’ll cover some of those in a future post. For now, just see if you can get out and gaze up into Cygnus and into the elliptical arms of our own home galaxy. There are little gems and surprises awaiting you!

Image courtesy of Sky Safari.

02 October 2019

Time to restart - October 2019

It's been two years since I posted on this blog. It's time to restart. Since I started this blog I moved from San Francisco, California to Munich, Germany. Here the skies are slightly different and the weather is not nearly as reliable so I am observing less frequently. However, I still want to write occasional articles that describe the astronomical highlights in the night sky, in particular those accessible to city dwellers. More to follow ....

31 July 2017

Perseid Meteor Shower 2017

The annual Perseid Meteor Shower will peak August 11 - 13, offering patient viewers a chance to see 10s or even 100s of meteors per hour if you view from a dark location. The Perseid shower is one of the year's best meteor showers, reliably delivering the twinkling and elusive flits of light that dash across the sky in sheer silence, sometimes in the north, south, east or west. Meteor showers are not for the impatient, but rather require a viewer to relax and enjoy the glorious summer night sky and simply stare up and wait while the Earth plunges through a rich meteor stream. From your location on the planet you need to simply have a big view (the more unobstructed, the better) and somewhat or very dark skies, and then some degree of focus on .... well ... nothing. Just by looking up and gazing, you will see the meteors.

Meteor Shower
Meteors have a delightful and tantalising way of appearing with a burst of light, moving at incredible speed for maybe 1/4 or 1/2 second, and then vaporising and flickering out as fast as they arrived. During a shower like the Perseids, you can rest assured that they are happening all around you all the time but the majority are just too small and too faint for our eyes to perceive. And you can also rest assured that many more are happening outside of your line of sight, as they may appear behind you or to your left or right and elude detection. So one of my favourite ways to see a meteor shower is with a group where you have many pairs of eyes on the sky and many reports of 'ooh, look at that' or 'wow, that was great' happening all around you. It is a wonderful communal activity that keeps the momentum strong since meteor showers, when viewed alone, can go for many minutes without producing anything. Teamwork ensures that no meteor is left unseen. So if you have a chance, join a group (or just find a few friends) who will be staying up to see what they can see.

The Perseids this year will be competing with moonlight each night. In San Francisco, the waxing gibbous moon rises at 10:37 pm on Friday 11th, 11:12 pm on Saturday 12th, and 11:49 pm on Sunday 13th. So take in the view while the moon is below the horizon and enjoy a few hours of meteors each evening. Meteor showers tend to get better as the night goes on, so Saturday and Sunday offer better chances of seeing meteors than Friday. Best of luck, enjoy, and have fun!

29 June 2017

The Summer Sky Awaits

The magnificent summer sky awaits, with dazzling views into our home galaxy, a host of first magnitude stars that enhance some of the finest constellations in the night sky, planets that shimmer in a telescope or binoculars, a meteor shower, and of course this year only (!) a Great Eclipse.

The Milky Way: although the cloudy band of stars that make up the central plane of our home galaxy is not visible in cities, binoculars still reveal many of the fine structures to be found in the Milky Way, albeit less spectacular and colorful than the dark sky view. Nonetheless, a leisurely tour from due south (between Scorpius and Sagittarius) to zenith (directly overhead) will reveal numerous clusters, nebulae and colourful groupings of stars.

Summer Highlights (click to expand)
First Magnitude Stars: The Summer Triangle features Vega, Deneb and Altair in a bright triangle rising from the east to tower overhead in mid-summer. Other top-10 stars include Arcturus and blue-white Spica in the west and orange-red Antares in the south. 

Planets That Shimmer: Jupiter continues to dominate the southwest sky, gradually moving toward the west as summer wears on. Saturn, just past opposition and glowing a bright milky white near Antares, is visible nearly all night tracing out a low arc across the southern sky from east to west. 

A Meteor Shower: the Perseid Meteor Shower peaks on Aug 11-12, and the waxing moon will be a distraction but not a particularly bad one given the circumstances. It's always a pleasure to find a dark spot and a blanket or easy chair for enjoying the bright flashes and streaks of light that punctuate the warm summer night. 

A Great Eclipse: Need I say more? So much has been written about this once-in-a-lifetime event on August 21st already but if you can't get enough then check out this website. And just do it. Drive to the Centerline. Really. 

Enjoy the many highlights the summer has to offer! 

Image courtesy of Universe2Go

30 April 2017

Now is the time to view Jupiter

Hubble Image April 2017
Jupiter is the brilliant 'star' that is currently dominating the evening sky, outshining all other celestial objects except the Moon. The largest planet in the Solar System, Jupiter is on the Top 10 viewing list for every backyard astronomer because it is easy to find and offers such richness when viewed with magnification, and of course it is dazzling whether viewed from the darkness of a country setting or the bright lights of an urban setting. And having just passed opposition in early April, Jupiter is well positioned for viewing shortly after sunset and is above the horizon nearly the entire night; being just past opposition also means that Jupiter presents the greatest surface area for viewing. A casual glance toward the south-east in the evening is all you need to find Jupiter.

Intricate Details on Jupiter
The image on the right from Sky & Telescope shows the intricate details visible on the surface of the planet. Any telescope of good quality will reveal the major bands on Jupiter's Northern and Southern Hemispheres, and a CCD will capture the Great Red Spot and some of the patterns in the clouds. The four largest moons of Jupiter add a dynamic and ever-changing view to the planet, with regular transits and eclipses adding live drama to an evening focused on just one celestial object. Sky & Telescope has an excellent article that highlights many of the things you can see on Jupiter - it's worth a short read. It also includes links to detailed timings of the transit of the Great Red Spot and the Jovian moon transits and eclipses.

NASA recently pointed the Hubble Space Telescope at Jupiter as part of its ongoing planetary exploration looking at not only the planet but its moons, each of which has an interesting geological history and aids in understanding the formation of the Solar System. This short video on HubbleSite provides further details on their work.

Jupiter is presently in the constellation Virgo just above the bright star Spica and slowly moving retrograde toward Porrima in the coming two months. Given the relative orbital speeds of the Earth and Jupiter, we see Jupiter in a different sign of the Zodiac each opposition; approximately every 12 months Jupiter has moved to the next sign. That means in a year Jupiter will be found in the constellation Libra, and a year later in Scorpius.

Images courtesy NASA and Sky & Telescope.

04 March 2017

The Spring Nighttime Sky Beckons

Spring Sky Highlights
Spring arrives on Monday March 20th and with it the ever-changing night sky with all it has to offer. The upcoming three months offer many celestial wonders, from Moon + Planet pairings to Meteor Showers to the arrival of Leo and Virgo high overhead as Orion and the winter beacons gradually fade into the western sky. Mercury makes a strong showing in April while Venus fades out of the evening and emerges in the morning sky.

The Infograph from Universe2Go showcases these highlights quite nicely. Look ahead for opportunities to get out under the night sky in the coming months and savor all that the universe has to show you.

09 February 2017

Penumbral Lunar Eclipse of February 10, 2017

Penumbral Eclipse
Friday evening the Moon will have a close encounter with the Earth's shadow 240,000 miles out in space. As the Moon reaches its full phase just after sunset (from the west coast), it will darken somewhat as it passes through the light outer shadow of the Earth. This shadow is called the 'Penumbra' and is not as dark as the central 'Umbral' shadow so this won't be a blood Moon or anything even close to that. But for the careful observer it will be an interesting sight as the Moon rises in mid-eclipse and displays a darkening on its upper limb as it enters the Earth's penumbral shadow. The Moon rises at 5:45 pm for viewers in San Francisco and will already be well along in the eclipse for viewers in the eastern USA and Europe.

This eclipse marks the start of an 'Eclipse Season' in which we will experience one Lunar Eclipse (in this case a Penumbral Eclipse) and two weeks later a Solar Eclipse (in this case an Annular Eclipse visible only in the southern hemisphere). Eclipses come in waves approximately every six months and this particular Eclipse Season is the last one before the Total Solar Eclipse of 2017 across the United States.

Sky & Telescope has an excellent online article detailing the February 10th Penumbral Eclipse in much more detail.

Image courtesy Sky & Telescope.