Archive for the ‘Transit’ Category


Observing report: the transit of Mercury from western Colorado

May 19, 2016

Mercury transit 9 May 2016 - telescope setup

I was in Utah from May 4 to May 15, chasing dinosaurs with Mike Taylor, a colleague of mine from England. I took a telescope along in hopes of getting some dark-sky time, and to hopefully catch the transit of Mercury on May 9.

Things did not look promising at dawn on the 9th. I was in Fruita, Colorado, and when I got out of bed, the sky was completely overcast. Mike and I decided to head out west of town to visit Rabbit Valley, where a nearly complete skeleton of the long-necked dinosaur Camarasaurus is visible in a hard sandstone ledge. (Why is no-one excavating this dinosaur? Because we already have many nice specimens of Camarasaurus, and the sandstone around this one is like concrete. It would be a mountain of work for very little payoff.)

We spent about two hours measuring and photographing the skeleton, and as we did so, the clouds started to break up a bit. By the time we got back to Fruita, a little after 11:00 AM, the sky was clear except for a few scattered wisps of cloud. I set up my telescope in front of the Dinosaur Journey museum and started watching and photographing the transit.

Mercury transit 9 May 2016 - Mercury crossing the sun

I was using the same setup as in the last post: my Celestron C80ED refractor, a Celestron 8-24mm zoom eyepiece, and a GoSky full aperture solar film filter. For photography, I used a Nikon Coolpix 4500 for still photos and my iPhone 5c for video.

I caught about the last hour of the transit, and I got to share the view with about a dozen museum staff and passersby. A few light clouds drifted through the field of view, which looked pretty cool and didn’t obscure the view at all.

At 12:42 Mercury finished exiting the disk of the sun. The next Mercury transit will be in 2019 – I hope I’m as lucky then as I was this time.


Getting ready for Mercury

April 18, 2016


The planet Mercury will transit the sun on the morning of Monday, May 9. Mercury transits are not as rare as the more famous transits of Venus, but they still only come around once or twice a decade on average. The last Mercury transits before this one were in 2003 and 2006, and the next two after this year will be in 2019 and 2032. From southern California, the transit will already be underway when the sun rises at 5:57 AM, maximum transit (the point when Mercury is the furthest inside the sun’s disk as seen from Earth) will be at 7:58, and Mercury will exit the sun’s disk between 11:39 and 11:42 AM (all times in PDT).

For the transit of Venus in 2012, I used a simple homemade device called a “sun funnel” attached to a small reflecting telescope to project an image of the sun. You can read more about that here and here. The sun funnel worked well enough – I also used it for the annular eclipse in 2012 and the partial eclipse in 2014 – but the screen material degrades the resolution somewhat. Mercury is a lot smaller than Venus, and much closer to the sun, and both of those factors make it appear much smaller than Venus during a transit.


I want maximum resolution for observing and photographing the upcoming transit, so I finally sprung for a full-aperture solar film filter for my 80mm telescope, which you can see set up at the top of this post. I got it out the other day for a test drive and got some decent photos of the current large sunspot AR2529, shown above. I’m pretty happy with the results – now if we can just get clear skies on the morning of May 9. If you’re curious, the filter I got is the GoSky Optics full-aperture filter with Baader solar film. There are several sizes available to fit all kinds of telescopes, and the filter attaches securely to your telescope tube or dewshield with three nylon-tipped screws. I got the filter for telescopes 81-113mm in diameter (outside tube or dewshield diameter, not optical diameter!), which is currently a little under $50 on Amazon.

This is my second GoSky product, after the universal cell phone adapter I picked up last fall, and I’ve been impressed with the solid construction and good fit-and-finish of both products. Some of the weird large-scale blotchiness in sun photos is probably either distortion from the iPhone’s tiny field lens, or gunk on the surface, and the uneven margin of the solar disc is from atmospheric turbulence. But I think the graininess across the surface of the sun is actual solar granulation. I couldn’t see it on the iPhone – not enough image scale. If I had, I’d have thrown in a shorter focal length eyepiece and tried some higher-magnification shots. They might not have turned out well even if I had taken them – the seeing was pretty awful – but it would have been worth a shot. Something to try next time.

The diameter of the sun is 109 times that of Earth. Here's how Earth would compare to the current large sunspot if they were side-by-side.

The diameter of the sun is 109 times that of Earth. Here’s how Earth would compare to the current large sunspot if they were side-by-side.

Unfortunately, I won’t be here in California to share the transit with my local friends and fellow observers. I’ll be in Utah chasing dinosaurs from May 4 to May 14, so I’ll have to catch the transit from there. I’m driving up and bringing my 80mm scope to take advantage of dark Utah skies in the evenings. If you want to plan your own transit observation, or just want to investigate how the transit will appear from various points on Earth’s surface, this interactive map is excellent. And if you need safe, inexpensive ways to observe the sun, check out my page on safe solar observing. Clear skies!


Observing report: the transit of Venus in Claremont

July 4, 2012

Here, just one day shy of being one month overdue, is my post on the transit of Venus on June 5. As promised, I took scopes downtown and did some sidewalk astronomy, and eventually some rooftop astronomy. As with the solar eclipse on May 20, the primary instrument was my son’s Astroscan with a homemade sun funnel, and once again it performed beautifully.

My partner in this enterprise was fellow Claremont paleontologist Matt Benoit. He was there for the whole thing, and helped keep scopes on target and help people understand what they were seeing. We hit a grocery store beforehand for soda and snacks and basically made an extended party out of the event.

I wanted to see the transit, period, but I was especially keen to watch the entry of Venus onto the solar disk to see if I could spot the “black drop effect” that bedeviled transit-timers in previous centuries. Sure enough, as Venus started to pull away from the limb of the sun there was a persistent dark blob or zone that seemed to connect the planet to the black space beyond, like surface tension keeping a drop of water from falling off the faucet. The black drop effect was once thought to be an effect of the atmosphere of Venus, but it’s not, because airless Mercury shows the same effect during its transits (the next of which is coming up in 2016, by the way). It’s nothing to do with our visual perception, either, since it’s easily recorded photographically, as you can see above. It’s now understood to be an effect of diffraction when a vanishingly thin line of light separates two darker spaces or silhouettes. You can see it by holding your finger and thumb up to the light and bringing them together–just before they touch, the black drop effect will seem to bridge them.

Along with the Astroscan and sun funnel, we had along the Celestron Travel Scope 70 with the aperture mask and solar filter described in this post, for direct viewing. Here’s my friend Marcy, who was there with friends for about half of the transit, getting her first look.

Although we both put in time on both scopes, for the most part I drove the Astroscan while Matt minded the Travel Scope. He also helped people get some photos through the eyepiece, as he did here with Marcy’s DSLR.

The view through the filtered scope was not as detailed as in the sun funnel, but the warm yellow color was more aesthetically pleasing, and many of our visitors appreciated both views.

Like the eclipse, the whole effect of the transit was a little unreal. In addition to the scopes, we also had eclipse glasses and a piece of welder’s glass. Every few minutes we would look up with our naked eyes and see a little black dot on the sun, and know that it was a whole world. And not just a world, but a twin of Earth. Someone on Mars watching a transit of Earth would see something very similar–our whole planet, all our evolutionary and human history, everything we’ve done or built (except for the handful of tiny things we’ve sent away)–all shrunk to a point, no larger, to the naked eye, than the period at the end of this sentence.

We had a steady stream of visitors downtown until a little after 6:00, when the theater blocked the view of the sun from the public square. So we decamped to the top of the parking garage across the street. Some people followed us over from downtown, and some found us up there on their own. One guy said that he found us because he had Googled for Venus transit events in Claremont and found my morning-of invitation post, which is nice, because that’s exactly why I put it up. In all, about 85 people saw at least some part of the transit through one of our scopes.

My son, London, watching the very tail end of the transit with the welder’s glass.

Venus was still crossing the face of the sun when they set together. As with the eclipse, I managed to get a shot right when the world crossing the sun touched Earth’s horizon. A moment later, it was gone, and the last transit of Venus until 2117 was over. I’m glad I got to see it, and to share it. I hope you had the opportunity to do the same.


See the transit of Venus in Claremont

June 5, 2012

If no clouds come to spoil the fun, I will be in downtown Claremont this afternoon (Tuesday, June 5) with a scope set up for free public viewing of the transit of Venus. The transit starts at 3:06 PM, PDT, and will still be in progress when the sun sets at 7:59. I plan to be there for all of it. If all goes well, from about 2:50 onward I will be in the public square in front of the theater, on the northeast corner of First Street and Indian Hill Boulevard. Whenever the sun gets low enough to go behind the theater, I’ll head up to the top of the parking garage across the street, to watch the sun set with Venus still crossing the solar disk. You, whoever you are, are welcome to join me.

If by some freak chance it is cloudy this afternoon, I’m going to throw my gear in the car and run up to Big Bear, which gets more sunny days than almost anywhere else in SoCal (that’s why the solar observatory is there). In which case, you’re still welcome to join me, if you can find me. Try the Discovery Center on the north shore, if it’s sunny…or the nearest pub if it’s not.

Fingers firmly crossed for clear, sunny skies!


Transit of Venus comic book!

June 1, 2012

This is awesome: the National Centre for Radio Astrophysics in India has produced a freely-available 16-page comic book on the transit of Venus, and it’s already available 11 languages and will soon be translated into at least 10 more. (I know, they call it a graphic novel, and that’s fine, but my inner fanboy rebels at calling any single-issue comic of less than, say, 50 pages a ‘graphic novel’. Also note that the June 6 date listed on the cover is for the transit as seen from India–as noted inside, in the Western Hemisphere the transit will be visible on June 5.)

I just finished reading the fine nonfiction book The Transits of Venusby William Sheehan and John Westfall, which covers all of the observed Venus transits in exhaustive detail and includes data for the unobserved (so far as we know) ones in antiquity. With most of that information still in my memory, I was impressed at how much the author and illustrator–Niruj Mohan Ramanujam and Reshma Barve–of the comic were able to cram into 16 pages (actually more like 12 if you don’t count the cover, license page, and a couple of blank pages). The book explains what transits are, why they were important historically, why they’re still important, and how, when, and where to observe the upcoming one safely. It’s free and cool, go check it out.


Awesome Venus transit simulator

May 29, 2012

In an earlier post I linked to a Venus transit calculator, which is pretty sweet, but now there’s an even better one. Here’s a screenshot:

You put in your location (latitude and longitude, or click the map) and it shows you a movie of the transit from your location with contact times and places (on the limb of the sun) and sunrise or sunset if those interfere. Very slick, and takes a lot of the guesswork out of setting up for the transit. It will even spit out screenshots with a button-click, which is how I got this one. Check it out.


Transit of Venus resources

February 17, 2012

I mentioned a couple of posts ago that there will be a transit of Venus across the face of the sun on June 5/6, an event that comes along only twice per century. The last one was in 2004, and the next one will be in 2117. I’m starting to collect online resources that have to do with the transit, and I’ll probably set up a separate page on the sidebar to make them easier to find (hey, look, I did!). For now, though, here are the two best:

Transit of Venus .org is probably the most comprehensive online resource for the upcoming transit, with links to tons of other transit sites and resources.

Astronomers Without Borders have an excellent transit page and blog going here. Particularly useful is their Local transit times page, which will show you the timing and path of Venus in front of the sun depending on your location. Here’s a screenshot of the map I generated for Claremont, California:

Note that the transit will still be in progress when the sun sets at 8:00 PM, so I’ll see about 80% of the transit (assuming no clouds!) but not the whole thing. I’ll take what I can get!

Also at that site is a sweet set of instructions on how to build a “sun funnel” projection screen to show lots of people the sun at once with a single telescope. Here’s a pic borrowed from the site of the sun funnel in action:

I am SO building one of those!