Tag Archive | venus transit across the sun

Closer to Home

As I write this blog post, the transit of Venus is ongoing, with Venus finishing  its slow march across the face of the Sun in less than an hour. The next time this will event will come around will be well after out life times in December 2117. The internet has been abuzz with these breathtaking images of the transit from all over the world from space telescopes,ground-based telescopes, even iphones strapped to solar eclipse glasses(!). I wanted to share my impressions of the event and how that ties into what we do at Planet Hunters .

For me personally, I wasn’t expecting to see the transit of Venus from New Haven. Yale’s Leitner Family Observatory was planning events, but it was cloudy starting in the morning, and it was predicted to be that way all day. I still packed the eclipse glasses, that I had gotten from the conference in Japan that I was at a few weeks back (the conference ended the day before the annular solar eclipse),  in my bag before heading out this morning. I was hoping but  not holding my breath for there to be a clearing of the clouds later in the afternoon, but it had rained midday. The clouds were thinning a bit in the afternoon, teasing with some small glimpses of the Sun or a brief moment where the sunlight could be seen trying to peak through. I remember on one of my first observing runs, when the weather was bad talking to the lead observer, the older graduate student in my research group. I remember her telling me about sucker holes in clouds, holes in the otherwise thick cloud cover. They happen, but not go to chasing them with your telescope because the can close and move just as fast as they appeared. I was hoping maybe we’d get a clearing in the clouds but it didn’t look like it was going to.

I was already resided to the fact I was going to be watching online on the live streams. I had even lamented to Chris who’s in Norway, in the land of the midnight Sun, for the transit who also had clouds from horizon to horizon for the start of the event. I got on the bus to go home, and noticed what I thought was sunlight on the buildings. I got off a few stops later so I could walk the rest of the way home (or to the observatory  just in case), and low and behold – a sucker hole had opened and there was the Sun struggling but nearly all the way out of the clouds staring back at me right above the astronomy building. I pulled out those eclipse glasses and my own eye glasses (that I rarely wear) and there it was. A bit of cloud still coming over in waves across the Sun’s disk, but there was a black spec on the top right. That was Venus! I made it to the Leitner Observatory where the other postdocs and grad students were, sharing our eclipse glasses to the members of the public who had come to the event and were in line to see through the solar telescopes. We also also got a chance to see the transit through solar telescopes. I captured a neat image from a solar spotter that an amateur astronomer (and also a fellow Planet Hunter) had kindly brought along. As the sun set, the clouds came back  as quickly as they had parted and the sky was covered and grey again. 

View of Venus and the clouds on the Sun’s disk from a sun spotter in New Haven

I have to say it was truly breathtaking and I hope you got to see it yourself and if you didn’t see it outside that you were able to view the transit online. It is amazing to think that that small dark sphere is really a planet moving in front of our Sun.

One of things for me that is so fascinating  is how our view of exoplanets has changed since the last transit of Venus, which occurred in 2004. Kepler hadn’t launched, we didn’t have over 2000 transiting planet candidates (or Planet Hunters 🙂 ) Kepler really has changed how we view the universe around us, with extreme worlds orbiting two stars as well as  the first detection of Earth-sized planets, and the first set of planets orbiting in the habitable zone of their stars (meaning if they were rocky or had rocky moons they might be able to have liquid water pool on their surfaces).

The same way that Venus is blocking out part of the Sun’s light (about 0.1%), is the way we identify planets in the Kepler light curves with Planet Hunters. If aliens in another solar system could watch the Sun today/yesterday, they would see a drop in light of about 0.01% for nearly 7 hours indicating Venus’s presence. We see the drops in the light curves indicative of a planet orbiting their parent stars in the Kepler field. We’ve already found four new planet candidates that weren’t previously identified by the Kepler team but there’s something different in seeing the light curve compared to seeing the Venus transit live. I’ve always known these planet candidates we’re finding are marching across the disks of their parent stars, but seeing the transit of Venus it felt real. I’m heading back to spend the rest of the night  working on my next Planet Hunters paper, thinking about the transits and planetary systems we’re finding and it feels just a bit more familiar…..a little bit closer to home….

~Meg

PS. Fancy looking for some more transiting planets, come to the Planet Hunters website and give it a try.

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The Transit of Venus and the Scale of the Universe

I’ll start by introducing myself as I’m not involved in Planethunters, but Meg asked me if I could write an article for you here about the Transit of Venus after I mentioned on Twitter that I was enjoying researching the topic for a talk I’m giving. I’m a Research Fellow at the Institute of Cosmology and Gravitation at the University of Portsmouth/SEPNet (South East Physics Network), and I’m funded by The Leverhulme Trust as an Early Career Fellow to work on Galaxy Zoo science. I’ve been part of the Galaxy Zoo science team since 2008 and I lead the studies of the interesting class of red spirals which were found by Galaxy Zoo, and am also interested in the role bars seem to have in slowing down star formation in spiral galaxies. You can read blog posts I’ve done for the Galaxy Zoo blog, which include explanations of these studies at http://blog.galaxyzoo.org/author/karenlmasters/

On 5th/6th June 2012 Venus will pass between the Earth and the Sun. It’s shadow will cross the Sun taking about 6 hours in total, although the length of that which is visible varies significantly depending on where you live on Earth. In the USA the beginning of the transit will be visible as the Sun begins to set on 5th June, while in the UK we’ll see the end of the transit after the Sun rises on 6th June.

The planet Venus orbits the Sun inside the orbit of the Earth, and passes between the Earth and the Sun quite frequently. However the planes of the two orbits aren’t quite aligned, so most of the time Venus passes either above or below the disk of the Sun. Actual transits are rare, but very predictable. They happen in pairs separated by 8 years, and then after each pair follows a period of either 121.5 or 105.5 years without any transits. The 2012 transit is the second of a pair – astronomers around the world viewed the first transit of the modern age in 2004, and the next transit won’t happen until December 2117.

To view a transit of Venus does not need to be technically challenging, but in its simplest form involves looking at the Sun – so some safety precautions must be taken. You must never look directly at the Sun! Serious eye damage or even blindness could occur if you did that, so take this warning seriously! My advice for viewing the transit if you are not a keen amateur astronomer, or able to get to a viewing party, is to either get your hands on a pair of Safe Solar Viewers (like these ones from Astronomers Without Borders), or to view the event via a web cam (like this one from Hawaii where the entire transit is visible, or GLORIA which is planning to show feeds from Australia, Japan and Norway). This last method also has the advantage (especially for UK viewers) of not being affected by local cloud cover, and has exactly zero risk of eye damage! If you come to one of my talks I hope to have solar viewers to hand out.

So why should you care about a black dot crossing the Sun, or perhaps more pertinently, why do I, and an astronomer who studies galaxies, and works in a cosmology department care enough to write a blog post about it and give several talks? Well historically transits of Venus have been very important in helping astronomers understand the scale of the solar system, and from that the scale of the Universe. Basically when Venus crosses the Sun we know that it, the Sun and the Earth are all in a straight line. Very slight differences in the viewing angle from two observers on the Earth can then be used along with our basic knowledge of trigometry to measure the distance to the Sun. For over 100 years, the distance to the Sun measured this way was the most accurate measurement we had.

From knowing the distance to the Sun, we can use slight changes in the apparent position of nearby stars as the Earth orbits the Sun to get their distances (more triangles – this is called the parallax method), and from those stars we calibrate methods which use stars of known or estimated brightness to estimate distances to nearby galaxies, and we jump from distances to nearby galaxies to more distant galaxies and eventually the whole universe. The distances to faraway galaxies have taught us that the universe is expanding and started in a Big Bang around 15 billion years ago, and even if we go to the observations that suggest the universe contains a mysterious “Dark energy” (which won the 2011 Nobel Prize in Physics), they are ultimately based on us knowing the distance to the Sun. So that’s why I think it’s important.

Here in Portsmouth we’re running a workshop about the transit of Venus on HMS Warrior, in the Portsmouth Historic Dockyard. We plan to demonstrate the triangulation method by using it to estimate the distance from the Warrior to the local landmark “The Spinnaker Tower”. Two people will stand on the desk and we’ll mark out from them the direction to the Spinnaker Tower. Making one of the angles a right angle, we can then estimate the distance to Spinnaker (which is about 300m) by d = b/cos A, where A is the other angle, and b is the distance between the two people on deck.

Google Map image of Portsmouth including HMS Warrior (top) and The Spinnaker Tower (bottom).

This isn’t exactly the method used in the historical measurements, but it demonstrates the idea. Of course when observing the transit of Venus from two widely separated places on Earth, it’s not exactly easy to measure the angle between the sight lines. What Edmund Halley figured out in 1678 was that if you could measure the times when Venus stars and ends its transit you can get at the same information.

In all of recorded history, we have records of a total of six transits of Venus that have been observed (1639, 1761, 1769, 1874, 1882 and 2004). You have to feel sorry for Johannes Kepler, who predicted the transit which occured in 1631, but then died in 1630. No-one is recorded to have used his prediction that year. Jerimiah Horrocks and Willam Crabtree (two British astronomers who were friends) have the honour of being the first humans known to have seen Venus transit. Horrocks found and improved Kepler’s earlier predictions, and both men successfully observed the 1639 transit from Northern England (in December!).

Scientific observation of the transit started in the 18th century following Halley’s suggestion to use it to measure the distance to the Sun. There is a hugely rich and entertaining history of these expeditions to view the transit, and several books have been published. I’m just going to tell you a couple of the stories which struck my interest! A lot more, and links to some of the books can be found via the Wikipedia page on Venus TransitsTransitofVenus.org, and TransitofVenus.nl.

For the 1761 transit, two famous explorers got involved. Mason and Dixon (still in Britain, and before they set off to map the USA) were commissioned by the Royal Society to observe the transit from Sumatra. They met in Portsmouth, and set sail from here on HMS Seahorse (which a decade later would have a famous midshipman named Horation Nelson). Enroute to Sumatra they got attacked by the French (the French and English being at war then), and decided to give up. They wrote the Royal Society of their intentions and were promptly told they better get right back on the ship to observe the transit or else. They did, and eventually ended up viewing if from South Africa.

The 1769 transit also had some famous viewers. Captain Cook was ordered to set sail in HMS Endeavour, partially to observe the transit from Tahiti, but then to continue on and look for the mythical “Australia”. On that trip they didn’t find Australia, but they did land and claim New Zealand. And in Tahiti, they set up a “Fort Venus” from which to stay safe from the natives and view the transit. This voyage is being repeated this year in a replica vessel, and you can follow along at the HMB Endeavour Website.

These 18th century observations results in a measurement of the distance to the Sun of 153+/-1 million kilometers, which was a huge improvement over previous estimates, but not as good as they expected. The timings were thwarted by something which came known as the “black drop effect” where the shadow of Venus seems to bleed into the edge of the Sun. This meant that the start time of the transit could not be measured to better than a few seconds.

The black drop effect, photographed in 2004.

In 1874 several more expeditions set out, including several on Royal Navy Ships, such as HMS Volage, one of the largest mixed sail and steam ships ever built, which ferries the British expedition to the Kerguelen Island in the Southern Indian Ocean. Such measurements helped improve the distance measurement to 149.59+/-0.3 million kilometers. By 1881 it had been decided the distance to the Sun could be estimated better by other methods, although several expeditions still set out, and the first photographs of the transit were taken.

A photograph of the 1882 transit, taken by a US expedition.

The current best distance to the Sun is 149.5978707 million kilometers, +/- 3 metres, measured using radar ranging to the inner planets. It’s known so accurately that we can measure it’s changing, growing about 15 metres every century.

The first transit of Venus to happen in the modern age was in 2004. You can find videos of this event (like the one below), which I was lucky to view from a small observatory near Ithaca, NY while I was studying for my PhD in Astronomy at Cornell University.

For the 2012 transit, apart from encouraging people to view the event as a last in your life time chance, there are couple of new developments. First smart phone technology which didn’t even exist in 2004 has allowed the development of a “Transit of Venus Ap“. In this Ap you can input the time you view the transit starting and/or ending, and participate in a global experiment to measure the distance to the Sun. Download the Ap in advance to practice inputing your measurement.

Interest in exoplanets has also significantly grown, including the signature that the atmospheres of those planets might have in the observed spectrum of a star when the planet is transiting. The Hubble Space Telescope will try to simulate this type of observation during the transit of Venus, observing the light from the Sun reflected by the Moon (if HST looked at the Sun it would be destroyed) to search for the signature of the atmosphere of Venus. You can read more about the plans on the NASA website.
Anyway I encourage you to get out there, or get online and view the last transit in our lifetime. Use the resources attransitofvenus.org, to work out the timings of the transit from your location, or search for local events. Other useful resources are the Royal Astronomical Society page on the Transit of Venus, in the UK, the HM Nautical Almanac Office. Also of possible interest, the Royal Observatory, Greenwich has a Venus Transit page, and a special (free) exhibit running until September 2012. And of course there’s a special Planethunters page on the transit too.

Transit of Venus: Live

In June 2012 people all over the world will watch the planet Venus transit across the Sun. Planet Hunters is all about spotting planets as they move across the face of a star so we thought it would be good to share the event with everyone. Venus will pass directly between the Earth and Sun on the night of June 5th and the morning of June 6th. This historic event can be seen from many parts of the world and will not happen again for 105 years!

As the map above shows, most people will only see part of the transit. With the help of the GLORIA team, we’ll be showing a live feed of the whole event on the Planet Hunters site. The webcast is being streamed from Tromsø, Sapporo and Cairns and will feature commentary in English and Spanish during the key parts of the event.

Check out our guide to the Transit of Venus, which we’ll update as we approach the event itself. It covers a basic history of the transits, and include information on when and where to see it. It also links to other useful resources for the event, including a Transit Guide from the GLORIA group, and the NASA observers handbook links. We hope you’ll try to see the transit when it happens, but if you’re unable to for some reason, then the webcast means that you can still be a part of this last-chance astronomical event.