Explanation:
What's that moving across the sky?
A planet just a bit too faint to see with the unaided eye:
Uranus.
The gas giant out
past Saturn was tracked earlier this month near
opposition -- when it was closest to Earth and at its brightest.
The featured video captured by the
Bayfordbury
Observatory in
Hertfordshire,
UK
is a four-hour time-lapse
showing Uranus with its four largest moons in tow:
Titania,
Oberon,
Umbriel and
Ariel.
Uranus' apparent motion past background stars is
really dominated by
Earth's own orbital motion around our Sun.
The cross seen centered on
Uranus is called a
diffraction spike and is caused by light
diffracting around the four arms that hold one of
the telescope's mirrors in place.
The rotation of the diffraction spikes is not caused by the
rotation of Uranus
but, essentially, by the
rotation of the Earth.
During the next few months
Uranus itself will be visible with binoculars,
but, as always, to see its moons will require
a telescope.
