Human Journey

Venus transit observations under cloudy skies

Last Tuesday, Venus passed directly between the Earth and the Sun.   Such transits are rare events.  They come in eight-year-apart pairs but the pairs are separated by more than one hundred years.   The next transit event will not take place until 2117.  So, astronomers, both professional and amateur, eagerly awaited (and prepared for) this event.   The forecast in NJ was marginal at best.   I set up my small telescope with a DSLR camera to take pictures from the top of the local parking garage about an hour before the transit was to start.   Here’s how the skies looked from my observing site…

Cloudy skies for the transit

Needless to say, I was expecting a complete washout.  However, occasionally, the Sun partially peaked through the clouds allowing me to grab some quick snapshots.   Here’s one such photo…


Venus' silhouette on the Sun seen through clouds
Venus' silhouette on the Sun seen through clouds

By stacking several of these single images together, it was possible to produce the image shown at the top where the clouds have essentially been “averaged out” of the picture.

By the way, it is possible (and fun!) to view and photograph Venus in the daytime.   Here’s a picture I took just 2.5 days before the transit event started (in the morning when the skies were perfectly clear!)…

Daytime picture of Venus 2.5 days before transit.
Daytime picture of Venus 2.5 days before transit.

It is interesting to note that, in this picture, the crescent extends more than halfway around Venus.   This extended glow is proof that Venus has an atmosphere.   No atmosphere and the crescent would be just a crescent, nothing more.   But, here the extra glow is caused by the Sun illuminating the atmosphere even on the side where the Sun has “set”.

Many more pictures both before and during the transit can be found at my website:

Even though we have to wait more than one hundred years before we’ll be able to witness another transit of Venus across the face of the Sun, we only need to wait slightly less than four years for Mercury to do the same thing:  May 9, 2016.  Mercury being smaller and further away from us and lacking the historical significance, it won’t be quite as dramatic as the Venus transit.   But, it will be worth watching it too—it’s not every day that we get to “see” a perfectly round black silhouette of a planet transiting across the face of the Sun.

Robert J. Vanderbei is chair of the Operations Research and Financial Engineering department at Princeton University and co-author of the National Geographic book Sizing Up the Universe. Vanderbei has been an astrophotographer since 1999, and he regularly posts new images on his astro gallery website.

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