seeing Uranus move

Last Wednesday, as well as getting a SeeStar photo of the Crab Nebula, we also took a picture of Uranus.

5 minute exposure : can you spot Uranus?

The problem is, Uranus looks like a star at the resolution of this telescope.  But, planets wander; it's there in the name.  So, we took another picture on Saturday, when we were also looking at the Orion Nebula.  Putting the two images side by side makes it clear which spot is the wandering planet, and which spots are the fixed stars.

 18 March, 5 minute exposure                                     21 March, 2 minute exposure

Blinking between the two images shows the movement well (but also shows that one image is very slightly rotated with respect to the other).

So how far across the sky does Uranus move in 3 days?  Well, its orbital period is 30,688.5 days, during which time it travels once round the sky, through 360 × 60 arc minutes.  In 3 days, it will therefore travel about one ten thousandth of this, or just over 2 arc minutes, or about 1/15th of the angular diameter of the moon.  So definitely enough to be visible.

my sixth planet

I’ve seen all the naked eye planets: Mercury, Venus, Mars, Jupiter, and Saturn.  In fact, Venus, Mars and Jupiter have all been readily visible the last few nights.

But tonight was a first: Uranus is quite close to Venus, and so finadable with binoculars, particularly with the 15×70 pair we bought for comet ISON (but then never saw comet ISON). So, tonight I saw Uranus for the first time.

Some people can allegedly see Uranus with the naked eye; I certainly can’t.  And with tonight’s slightly hazy sky, it was a very faint dot, even with binoculars.

Phil Plait’s photo of Venus and Uranus

I didn't manage a full four planet night this time, as Mars was too low by the time I went out, but still.  Six planets!