The Search Has Landed – December 2011

This is the (semi)monthly feature in which I catalog the most notable searches that have landed at this site and do my best to answer any burning questions they might entail.

What observational technique allows astronomers to determine that Venus is rotating backwards?

Good question. Venus is shrouded in a cloudy, totally featureless atmosphere that prevents us from seeing it surface, so it’s impossible to determine rotation by telescope observation.

But we have imaged Venus’s surface with cloud-penetrating radar. And do you want to know the amazing part? We first did this from Earth. So from Earth, we bounced a radar beam off of Venus and found features big enough to see from here that allowed us to determine its period (and direction) of rotation.

We have since sent exploratory probes to Venus and probed its surface in much greater detail, but I don’t think sending probes counts as an “observational technique”. But sending radar from Earth does count, even if it’s not something amateur astronomers are equipped to do. Besides, it’s really cool, to boot.

 If you lived at the equator, what differences would you notice between the solstices?

The solstices (winter and summer) are the moments in time when the sun is farthest north, or farthest south in the sky. Even from the equator, the sun on the December solstice will rise south of due east and set south of due west. And on the June solstice, the sun will rise north of due east and set north of due west.

Other than that, I can’t think of anything.

Google Sky Map can’t find moon

Deepak? Is that you?

If a planet has a tilt of 15 degrees, what would be the line of latitude of the Tropic of Cancer?

It’s actually as simple as can be. The Tropic of Cancer would be 15 degrees north, and the Tropic of Capricorn would be 15 degrees south since these would be the boundaries of the sun’s north-south sweep through the sky throughout the year.

I love it when things are simple. Not like that Venus thing.


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