The Great Conjunction of Jupiter and Saturn - Dec 21st, 2020

We will witness a very rare and beautiful spectacle in the coming days. On December 21st, Jupiter and Saturn will be less than one-tenth of a degree apart from each other as seen from Earth, a rare alignment that happens only every 400 years at this extremely close separation. 

The Great Conjunction

Great Conjunction: Conjunctions occur often in the heavens, as heavenly bodies pass near each other, on in the less common scenario where the Moon covers stars and occasionally planets, and as planets and asteroids cover stars. In any case, a conjunction is usually a fascinating thing to see, particularly up close if you have binoculars or a telescope. When Jupiter and Saturn pass near each other every 20 years, we have a 'Great Conjunction' in which the two massive planets are very near each other. But every 400 years, the alignment is extremely good and we have both objects in one telescopic field of view, as portrayed in the image to the right. 

How to See It: The two planets will be visible only for a short while after sunset, and you will need a clear view to the west to see this. Look directly to the southwest of the point of sunset an hour after the sun goes down. If you have a telescope or binoculars, this is definitely the time to get them out and put them to work. If you can, look for the pair on Saturday 19th or Sunday 20th to get an idea where to find them. They will be in roughly the same place on the 21st, but through the telescope or binoculars the difference from one night to the next will be dramatic. 

Learn More: There are excellent articles online if you want to learn more about this rare and exciting event, on Scientific American or Earth-Sky. I find all of the detailed planetary geometry fascinating, and fun to understand how such alignments occur and can be accurately predicted. 

I wish you clear skies and happy viewing! 

Image courtesy Earth-Sky. 

Geminid Meteor Shower 2020

The Geminid Meteor Shower peaks on Sunday 13th and Monday 14th. This year, it will be especially well timed with the New Moon, meaning that there will be no moonlight to brighten the sky, leaving the sky dark and at its finest for a meteor shower. 

Fireball

What causes a meteor shower? Every day, there are dust particles and small objects flying into the Earth's atmosphere from space, sometimes randomly, sometimes predictably, causing a 'shooting star' in the night sky. And sometimes with great surprise, a larger piece of an asteroid will fly into the atmosphere and become visible as a Fireball, as was the case two weeks ago in Japan. The Geminids are predictable, one of many annual meteor showers that are caused when the Earth travels through the remnants of a comet or asteroid that has orbited the Sun sometime in the past, leaving a debris stream in its wake. 

What causes the Geminids? Every year on December 13th and 14th, the Earth travels through such a wake (of an asteroid named 3200 Phaethon) and we have a lovely meteor shower, as the dust and sand particles impact the Earth's atmosphere at high speed and heat up the air, causing it to glow as the meteor hurtles toward Earth. Nearly all of the particles in a meteor shower never reach the surface of the Earth, but those that do (called Meteorites, once they've landed) are of great scientific interest. 

How to see the Geminids: For any meteor shower, you want to find a dark location where you have a wide horizon. You don't need to look in any one direction, but ideally relax on a blanket or chair and simply look up, and have patience. And of course, for most of us it's winter and it's cold, so you need to dress extra-warm. 

If you want to learn more, this helpful article from Astronomy Magazine provides a great deal of information about the Geminids. 

Happy Viewing, and stay warm! 

Image courtesy of ESO. 

Share the Night Sky - Broadcast on KPOO

During the recent Bay Area Science Festival, I had the privilege of sharing the night sky with DJ Marilynn and the listeners of KPOO during a special broadcast on Thursday evening October 22nd. Our hour-long broadcast features many different topics: 

• How to find a good spot for stargazing in the city, and how to prepare for looking at the night sky. 
• How to find planets such as Jupiter, Saturn and Mars this fall and winter, along with the constellation Sagittarius. 
• How to find the Summer Triangle and connect it to the Milky Way. 
• How the view of the sky changes when viewing from different places around the world. 
• How to understand the motion of the constellations in the northern sky, featuring Cassiopeia and the North Star. 
• How to enjoy a view of Orion the Hunter later in the evening. 
• How to further your experience with the night sky. 

Click here to listen to the broadcast. 

Image courtesy of KPOO-FM.

A Fall Triangle

There are popular alignments of the stars that mark summer and winter, but not in the fall ... that is, until Thursday October 22nd when we will have a brief but impressive 'Fall Triangle' as a result of the waxing Moon passing near Jupiter and Saturn in the evening sky. To see this you will need a clear view to the south, but the three objects are easy to find and a pleasure to view all in one compact triangle. If you have binoculars the view will be even more spectacular. The day before and the day after the Moon will no longer be close enough to form the triangle. So take a minute to savor the sky on the 22nd and you won't be disappointed. 

As an added bonus, take note of the position of Jupiter and Saturn. If you pay close attention over the next two months, you will see the gap between them closing day by day. Jupiter is heading for a conjunction with Saturn that will culminate in a very close encounter in late December. Keep your eyes on the sky! 

Image courtesy Sky & Telescope. 

Approaching Mars

If you have been attentive to the night skies lately, you've most likely noticed a very bright orange/red object in the evening hours toward the east. That is Mars, the Red Planet, and we are fast approaching Mars for a close alignment that will bring us to the closest approach in over two years, culminating on October 6th. It will remain a distinctive evening object for the coming months, but the month of October is when you will see Mars shining at its brightest. 

Every 26 months we have a close encounter with Mars. The last one, in 2018, was even closer than this year. However, for those of us in the northern hemisphere Mars was low on the horizon for most of the night. For the 2020 close encounter with Mars, we will get a better view of the red planet, as it will climb higher across the night sky in October and through the end of the year. 

In addition to the close approach on October 6th, Mars will be at opposition on October 13th. For more details about opposition, I recommend this Earth Sky article by Deborah Byrd (scroll all the way to the bottom for a great Mars Opposition chart). And if you have a telescope and want to use this close encounter to get a close up view of Mars and some of its surface details, I strongly recommend this Sky at Night article complete with weekly views of what to look for on the martian surface. I will take advantage of this month to try to make out the martian South Pole and some of the surface features with my 5 inch reflector, and I will report on that in a future post. 

Image permission Wikimedia Commons. 

Update on October 21st: I have tried to view Mars with my 5 inch reflector telescope. Unfortunately, that size telescope is simply too small to provide the resolution needed to see the features on the martian surface. I suspect that a camera and some long-term exposures could help, but without an 8- or 10-inch telescope, I don't think it will be possible to truly see the surface details with the naked eye. 

Late Summer Waxing Moon

Who doesn't like looking at the Moon? It's such a treat for everyone, and is a lovely sight. For us Northern Hemisphere dwellers, there is a unique period of time each year in the late summer when the waxing Moon plays out across a low swath of southern sky, never getting very high into the sky. That unique period of time is now, and the Moon is making things more interesting by passing close to Jupiter and Saturn. 

For the last many days I've watched the waxing Moon emerge from the new phase into a thin crescent and then slowly toward first quarter. All the while it hugged the southwestern horizon, keeping low in the sky and making it more challenging to find. Now the phase has advanced to gibbous (between first quarter and full Moon) and all the while, the Moon only gets high enough to be seen if you have a clear view to the south. And for me, when I see this low-flung Moon, I know it is late summer. There is a technical reason for this. The waxing phases of the Moon occupy the sky where the Sun will be for the coming six months ... and that will be in the Fall and Winter seasons where the Sun does not rise too high above the southern horizon. There is a beautiful symmetry to the Sun and Moon and since we have one complete lunar phase every 29 days, we can see the entire flow of the seasons every month if we know how to look at the Moon. 

Over the past several years the late summer sky has featured Jupiter and Saturn low in the south. This year Jupiter will overtake Saturn in a series of 'conjunctions' which have already started, and will run their course by the end of the year with a spectacular alignment of the two planets in December (mark your calendar for Dec 21st). Saturn moves around the Sun very gradually from our point of view, and Jupiter faster but still quite gradual from year to year. The effect of these gradual movements is that these two giants have been lurking low in the southern sky during the Summer for the past years and for the coming years ahead. So as I've observed this unique time of year when the waxing Moon traverses a deep southerly course in the late summer, it's had the added beauty of a monthly encounter with Jupiter and Saturn. That will happen this week, on Friday 28th. You will need a clear view to the southeast to really enjoy the spectacle. And who knows ... perhaps you will discover this lovely configuration and the low waxing Moon in late Summer as something you will look forward to every year. I sure do. 

Image courtesy of Sky & Telescope. 

Perseid Meteor Shower 2020

The Perseid Meteor Shower has already started and will peak over the coming days, on August 11, 12 and 13th. This shower is one of the most reliable meteor showers of the year and as it peaks during generally warm weather for the Northern Hemisphere, it's a pleasant and easy-to-watch astronomical event that can captivate and amaze. 

Seeing the Perseids: seeing any meteor shower is easy, but getting the most out of the evening takes a little planning. First of all, you want to find dark skies, ideally away from city lights. Second, you need to reduce all local lighting to a minimum, including houselights and if possible, streetlights (for example, move to a part of a garden or park where streetlights are not directly visible). Third, you need a comfortable place to relax, ideally on a recliner chair or on a blanket on the ground so you can simply look up in all directions. Finally, you need to have warm clothing because even after a warm day the evening temperatures can drop quite quickly and if you are lying still in the open air, you will very quickly feel the effects and the Perseids will lose their appeal. 

There are two more factors that has a big impact on seeing the Perseids, one you cannot control (the phase of the Moon) and one you can (when to watch). The Perseids in 2020 are better positioned than some years because the Moon will not rise until well after midnight, allowing more viewing time in the late evening and early morning hours. In general, the best time to watch any meteor shower is after midnight (for reasons you can read about here), so your best bet is to get out late evening to start your viewing, and stay out until the moon rises (if you can stay awake that long!). 

Why are the Perseids so reliable? The Perseids, like most annual meteor showers, are caused when the Earth travels through a debris field that is also orbiting the Sun. In the case of the Perseids, the debris field is from Comet Swift-Tuttle. The American Meteor Society has an excellent article that explains some of the science of the Perseids, if you want to learn more. 

Best of luck, and clear skies! 

Image courtesy of NASA. 

On seeing Comet NEOWISE

As suggested in this Sky & Telescope article from Bob King, "whatever you do, see this comet." We have a rare and wonderful opportunity to see a comet taking shape and revealing itself day after day. Comets come and go unexpectedly and often show promise that they might develop into something but then fizzle out and disappoint. Comet NEOWISE (also known as C/2020 F3) is living up to expectations and is now a naked-eye object visible in the early morning skies. You will need to get up early to see it for the next few days, but it is worth the effort. And if you don't manage to see it by the 15th of July, it will appear in the evening sky after that. The image on the right comes from a member of the San Francisco Amateur Astronomers, my old club, with NEOWISE over the Golden Gate Bridge. 

Image by Moshen Chan

The most important thing if you want to see NEOWISE is to have a clear view to the north, either the north-east in the morning or the north-west in the evening. This Sky & Telescope article provides detailed charts where to look for the next two weeks. As they point out, you will have best results for the next few days 1-2 hours before sunrise, or after the 15th 1-2 hours after sunset. 

I had to get up very early two days ago (3:00 am here in Munich) to see it. I took a short walk to the fields nearby my neighborhood where I had a clear view to the north and there it was, a lovely glowing coma and a long and smooth tail pointing upwards, away from the Sun, easily visible to the naked eye but a special treat in my 10x50 binoculars. If you have binoculars be sure to use them in the hunt. A telescope is unnecessary and the magnification will be too strong. 

Good luck finding NEOWISE and enjoy this rare spectacle. 

15 minutes about: Our Place in the Universe

How can we possibly comprehend our place in the universe? I discuss this topic frequently during star parties and enjoy sharing my thoughts about how we can relate to the universe in a more tangible way. I created a 15 minute talk about this as part of an innovative science talk series in Munich, 15x4 Knowledge. The talk covers the various 'levels of scale' that define our universe, from our home planet Earth through the Solar System, Milky Way galaxy, the Local Galactic Group, to the Laniakea Supercluster. As the name of the series suggests, four speakers give 15 minute talks in a single the evening and it was an honor to be a part of their program. More videos from 15x4 Munich can be found on YouTube.

Click here to view the video "15 minutes about: Our Place in the Universe."

Moon and Planets grace the morning sky

Moon and Planets - May 2020

This week, as the Moon passes through its waning phases, it will form some engaging patterns with three planets that are currently visible in the early (pre-dawn) skies. See image showing the change of location of the Moon from one night to the next, and the gentle interplay with Jupiter, Saturn and Mars as the Moon travels in its orbit around the Earth another 12 degrees eastward each day.

Jupiter has been gradually moving eastward as well, albeit considerably slower than the Moon. In fact, it takes Jupiter one full year (on Earth) to move the same 12 degrees eastward as the Moon does every day. And in addition, when we view Jupiter and the other outer planets from our view aboard spaceship Earth, we see a peculiar motion that takes Jupiter westward for a few months before continuing its eastward journey. We call this reverse motion 'retrograde' motion and in fact Jupiter is just now starting into retrograde and will return into the constellation Sagittarius for the summer before returning its eastward journey past Saturn into Capricornus at the end of the year.

This summer, Jupiter and Saturn will rise earlier and earlier and be visible the entire night from July onwards. But for now (in May) you will need to be up after midnight and before the break of dawn, around 4:30 am here in Munich, if you want to see this lovely morning alignment of the Moon and planets. I wish you clear skies and happy viewing!

Image courtesy Sky & Telescope.

The Starlink Satellites

I have always considered satellites a part of observational astronomy. As an amateur astronomer, I enjoy simply looking up and trying to understand what I see in the heavens above. If a satellite happens by and I can watch its gentle arc for a while, I find that interesting and it enhances my enjoyment of being out under the stars.

Recently, SpaceX has been launching 100s of satellites into Earth orbit. The Starlink Satellite system will deliver high speed internet around the world. As a spectacle, I find the Starlink satellites fascinating to watch since they move in very large packs across the sky, not just single satellites but groups of them that move like a string of pearls across the sky for minutes at a time. I've observed these on many occasions over the past weeks. To see them, you will need a somewhat dark sky and a clear view especially toward the west. The website Heavens Above provides accurate information to help you locate times when the satellites will be visible based on your location on Earth.

Heavens Above - Starlink Passes

If you want to try to see the Starlink Satellites, your best bet is to find passes on Heavens Above when they will be appearing, which is typically within 1-2 hours after sunset based on your longitude and latitude. For city viewers, you will need to find passes that are at a brightness (magnitude) of 1 or 2. Higher numbers mean fainter satellites and they will be hard to spot. If you are in a darker location, you will be able to see passes down to magnitude 3 or even 4. Click on the image to the right to see an example, in this case based on my location in Munich, Germany.

The passes are quite impressive, with the graceful slow movement of a satellite from west to east being followed by a next satellite, and 15-20 seconds later another satellite, and so on. These chains of satellites are quite beautiful to see and if you are patient and look closely in the direction that Heavens Above advises, you will indeed find them. But you have to really pay attention to the cardinal direction (Azimuth, shown as east, west, north, south) and the height in the sky (Altitude, shown in degrees above the horizon).

There is controversy about these satellites. Because of the sheer quantity of them and the fact that they are bright enough to spot nearly every night, professional astronomers and astrophotographers are being disrupted in their work. SpaceX says they are working on ways to make the satellites less bright as they move up toward their final orbital altitude. The jury is out and we shall see how these satellites evolve over the coming months.

Postscript: on May 10th, 2020: SpaceX is working on plans to mitigate the impact of the Starlink satellites in the night sky, using a 'sunshade' approach.

Venus passes through the Pleiades - April 2-3-4

Every eight years the path of Venus, as viewed from the Earth, crosses directly through the Pleiades star cluster. On April 3rd the bright 'evening star' will be directly in the center of the Seven Sisters, or Pleiades, and it will be a very fine target through binoculars. It can be found for the first 3-4 hours after sunset, due west. Venus is by far the brightest object in the evening sky so you should have no problem finding this.

Venus passes through the Pleiades

I just checked this evening (Thursday April 2nd) and already the juxtaposition of extremely bright Venus and the blue-white shimmer of the Pleiades is remarkable through my 10x50 binoculars. The good news is that the bright first quarter Moon to the upper left of Venus does not cause any issues seeing this spectacle, and given the brightness of both Venus and the Pleiades (as seen through binoculars) this will be visible even with the light pollution of a big city. But ... you will need binoculars to truly appreciate this.

The best view will be on Friday April 3rd, but it will also still look quite impressive on Thursday April 2nd and Saturday April 4th.

More information in this Sky & Telescope article.

Image courtesy of NASA APOD and Fred Espenak.

The Moon: where is it going to rise tonight?

Moonrise in San Francisco

An old friend, Scott in San Francisco, posted a question on Facebook and it caught my attention. He illustrated a quandary that he faced when observing the moonrise in San Francisco on two consecutive nights and wondered why the two locations were so different. Here is what he wrote: "I am puzzled ... Can someone explain how the moon changes its position so radically in one day? I created a hand drawing of the moon, its location, and time as it rose over the San Francisco skyline the last two nights." There are two (well actually three) factors at work here.

Before we dive into the specific factors, let's review the basics. The moon, like the sun, rises in the east and sets in the west, but of course the precise point of sunrise varies throughout the year. The sun rises either north of east in the summer when the days are longer, or south of east in the winter when the days are shorter. The full moon, which Scott was observing when he sketched the images last month, has an opposite behavior compared to the sun ... that is, the moon is in the opposite part of the sky compared to the sun and as such, in the winter the moon rises north of east (when the full moon nights are longer) and south of east in the summer (when the full moon nights are shorter).

In addition to that macro change in the position of the moonrise compared to sunrise throughout a year, there are daily changes to the position of the moonrise. The moon, being much closer to Earth than the sun, moves rapidly in its 29 day orbit around the Earth and from one day to the next is approximately 12 degrees further eastward in comparison to its location the night before. That is the main reason that a rising moon rises approximately one hour later each evening, and the primary factor that is illustrated in the drawing above. The Earth has to turn more to get to the place where the moon has moved, in this case from 8:00 pm to 9:00 pm/.

Moonrise position changing

But there is a subtle secondary effect that Scott captured in his sketch. That is that the location of moonrise is quite a bit shifted on the horizon. In this case, it is to the south from one day to the next, not just a later moonrise time but also a point on the horizon that is south of the previous day. What is happening here is that the moon's path around the Earth is quite similar to the sun's path around the sky and that is a path that follows the zodiac band around the sky, something also called the ecliptic. Because the moon follows this path, and in this special circumstance in which a full moon is observed on successive nights, the winter full moon appears to rise further and further south on consecutive nights until it finally moves to last quarter moon phase and then it will resume its travels northward (north of east) as it rises late each night. In fact, the moon is simply moving across the known Zodiac constellations of Virgo, then Libra (see image on left), and eventually Scorpius and Sagittarius, all of which are low on the horizon and low on the ecliptic, and therefore are part of the reason why the moon rises further and further south of east on consecutive nights in the winter. The image shows how the moon moves across the Zodiac from night to night, but it will take some creativity to juxtapose this on the eastern horizon to fully understand why the moon is further south of east on consecutive nights. Think about it. It requires some big picture thinking.

There is a third factor for the change in the location of moonrise on consecutive nights which is based on the moon's orbital inclination, but that requires fairly expert knowledge of celestial mechanics to fully comprehend so we will save that for another time ... or a star party.

Today is the full moon, March 9th, 2020. You can try to reproduce Scott's experiment now, looking closely at the eastern horizon and locating landmarks where you can spot the moonrise on consecutive evenings. For the next 3 or 4 evenings the moon will rise about an hour later each evening, and also will rise at a point further to the south of east compared to the night before.

I wish you clear skies and happy viewing.

TED Talk: How looking up to the night sky gets us to think deeper

As an amateur astronomer I have hosted many star parties, and as a public speaker I have talked about the topic of astronomy in many settings. In November 2019, I had the privilege of giving a short talk about astronomy at the TEDxTUM event in Munich, held at the Technical University of Munich. The talk is about 9 minutes long and captures the essence of why I do a lot of public-facing astronomy events. I hope you like it.

The Spectacular Winter Circle

Winter brings out the best in the night sky. Some of the finest stars in our galaxy are concentrated in a region of the sky that shines with an intensity that you just can't miss on a clear night. A collection of extremely bright stars form a nice shape that is fun to look for, the Winter Circle. This asterism features 5 of the 8 brightest stars in the entire night sky, and in total 7 very bright stars that glow in the south on long winter nights.

The Winter Circle

Given that all of the stars in the Winter Circle are bright, this is a relatively easy target for city dwellers who might not normally pay attention to the night sky. The stars are part of six different constellations covering a fairly significant part of the winter sky. January evenings feature the Winter Circle moving gradually from east to west across the southern horizon. Given the span of this asterism from the lowest point at the star Sirius (see diagram) to the highest point at the star Capella, you will need a fairly clear view across the southern sky. For me, it's easy to spot one or two constellations wherever I am, but seeing all six constellations and all 7 of the bright stars in the circle requires that I have a good horizon and not much else blocking the way.

Most people can quickly and easily find the constellation Orion, and from there you can start your trip around the circle. Rigel is a blue supergiant star that is one of the kneecaps of the hunter Orion, and it is one of my favorite stars because of the intensity and color. Orion's 'belt' can help you find two other members of the circle, by following the belt up toward Aldeberan and down toward Sirius. The other stars are then easy to find looking up and left of Orion toward Gemini, Auriga and Procyon.

Finding a wide open space on a clear winter night where the grandeur of the Winter Circle is on full display is one of my favorite things. The stars are rich and intense, and the utter size of the circle make the viewing of this amazing pattern worth the effort. Dress warm and savor the moment. You will be glad you made the effort.

Image courtesy of SkySafari.

Update: good article from Sky & Telescope on the Winter Circle. They call it the Winter Hexagon.