The Venus Transit Brings Up Parallax

A reminder that the transit of Venus across the Sun will be visible a little over 24 hours from now (starting before sunset June 5th in the United States.)  It’s the last of your lifetime, so make your plans now.  Weather forecast across much of the eastern U.S. is pretty bad, I’m afraid. Of course there will be many places to watch on-line.  For more information, I highly recommend .  Also, though you and I can’t see Venus right now (too close to the Sun), the SOHO satellite can: click here for the latest photo, updated frequently, which shows the sun (at center, blocked out) and the sun’s corona around it, and a white dot approaching the sun, which is Venus (ignore the white horizontal lines, which are an imagining artifact).

The transit of Venus was used, historically, to figure out how big is the solar system (the sun and the planets).  As I’ll explain tomorrow, it wasn’t that hard to figure out how large are the distances between the sun and the planets relative to one another, but getting the overall scale — the absolute distances — was a much harder problem.  The first measurement accurate to a couple of percent came from the transits of Venus in the 1760s.  I’ll explain (roughly) how this works tomorrow; the technique relies on the principle of parallax, a principle which lies behind our own ability to perceive depth, and is used by astronomers to measure distances to (relatively nearby) stars.

[Reminder: two events coming up in which I’ll be speaking:

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Science Down, Up, and Inside-Out

First, a couple of things you might like to read: There was a long-overdue article from the New York Times as to how, after eight years of cuts from the Bush administration during good economic times, followed by additional inevitable cuts during the Great Recession, formerly world-leading scientific research efforts in the United States are on the … Read more

The Longest Sunset

What would the Grand Canyon look like if it had sunset light without the sunset shadows?  Sunday’s annular solar eclipse provided a hint of an answer: Quite a first visit to the North Rim of the canyon.  Maximum eclipse occurred an hour before sunset, and the sun set with a small piece of the moon’s … Read more

Three Crescents and a Ring

Hi all! I said that posts would be sparse for a couple of weeks, but I didn’t realize quite how sparse! But I’m gradually getting back on-line here.

Right now, what’s occupying my attention for the next 48 hours is all in the sky: three crescents, and a ring. I’ll be brief, but if you want more explanation about the geometry involved, you might want to read my very relevant article about geometry and the beauty of the heavens.

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Some Good Reads

I’m preparing an article on a very important type of energy that I’ve avoided writing about so far — the energy that comes from the interaction among fields.  I’ve avoided it because it’s tricky to figure out how to explain it.  But it’s important, for this form of energy is responsible for all the structure in the universe, from atoms to galaxies.  The article’s not quite ready yet, so today I’ve just got some good reading material for you, including the heavy, the weird, the amusing, and the optimistic.

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Dark Matter: Now You See It, Now You Don’t

Two interesting claims about dark matter this week, and on the face of it, completely contradictory, but in fact, not obviously so. Before saying one word more, let me repeat my mantra — something that all physicists know but relatively few non-scientists appreciate — most claims of a radical new result turn out to be largely or completely wrong. This is not because physicists are stupid but because doing science at the forefront of knowledge involves using novel techniques that might have unknown pitfalls, and also because a single small mistake can create a fake effect (as we saw most recently with the OPERA neutrino speed measurement.)  And because nasty statistical accidents can play tricks on you.

Both claims that I’m about to describe use novel techniques, and their analyses have not been repeated by anyone else. At this point you should understand that both are tentative, and (based on the history of radical claims) the odds are against them. Both might be wrong. That said, both analyses look to me as though they’ve been reasonably well done, and if a mistake has been made, it will require someone far more expert in dark matter studies than I am to point it out.

So let me describe them in turn, to the best of my ability.

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Looking for Signs of Dark Matter at the Milky Way’s Center

There is going to be some amount of debate regarding dark matter in the next few weeks, so I’ve written an article on one of the best ways to go looking for new signs of dark matter out in space. The reason we are almost entirely convinced that the universe has lots of matter that … Read more

What to Watch in the Sky This Week: Beauty in Motion

Why does the sight of the Moon draw our gaze and silence our voices? What is it about the planets, those exceptionally bright points of light that wander among the stars, that we instinctively find so beautiful?  Is it perhaps that they make us dream of faraway, unreachable places? Is it that they are beacons … Read more