Page 95 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

WHAT TO SEESEE

Saturn is farther away from the Sun and smaller than Jupiter, so it’s
fainter and its maximum brightness varies more, from +0.8 to –3.3.
Its variable brightness is due to the way the rings are tilted and how
much sunlight is refl ected back our way. Saturn is not so bright when
the rings are edge-on to us, but its brightness increases over 7.5 years
as the rings open up to observers on Earth. Then it fades again over
the same period.
If you’re wondering why this takes 7.5 years, it’s a quarter of the
time Saturn takes to go around the Sun. Oppositions of Saturn over the
next few years occur on 28 April 2013, 11 May 2014 and 23 May
2015, when the Ringed Planet will be brightest.
The best way of understanding Saturn’s tilting effect is to go out
and look at the planet – it really is one of the telescopic marvels of the
Solar System. It doesn’t matter if you have a small scope: the sight of a
world surrounded by rings is amazing. I’ve seen Saturn through large SATURN
and small scopes and it’s actually the little ones that get my vote every
time. The view of this tiny ringed world hanging in a large, inky black
fi eld of view is magical. Larger Mean distance from the Sun:
scopes will start to show detail 1,427 million km
in the rings and on the planet. Rotation period: 10 hrs 47 min
Orbital period: 29.5 years
Diameter: 120,000km
Saturn is especially magical Gravity (Earth=1): 0.9
when its rings are tilted Mean atmospheric temperature: –185˚C
towards Earth
Number of moons: 34

URANUS Sadly, not all the planets are PLUTO
exciting. Uranus doesn’t have
much going for it, whether you AND ERIS
Mean distance from the Sun: use your eyes, a pair of binoculars
2.8 billion km
Rotation period: or a telescope. Turning your head Pluto and Eris are two
upwards, you can just see this
17 hrs 14 min examples of objects now
Orbital period: 84 years gaseous world as a very faint star defi ned as ‘dwarf planets’.
at the limits of visibility (around
Diameter: 50,800km Since 2006, the Solar
Gravity (Earth=1): 0.89 mag. +5.6). You won’t see much System has had eight
Mean atmospheric temperature: –214˚C from anywhere with light pollution planets and fi ve dwarf
– the sky has to be very black
Number of moons: 27 planets after 76 years of
indeed. The view does improve a there being nine. Included
little through a telescope, showing in dwarf planets are some
a greenish speck. of the more interesting
‘larger’ members of the
Uranus’s greenish colour is clear through a small telescope swarm of rock and ice
known as the Kuiper Belt
– the remnant of planetary
formation that lies beyond
Neptune. This may turn out
to be the most fascinating
At around mag. +8º you need at part of the Solar System,
least binoculars to see Neptune, NEPTUNE with its untouched,
and there isn’t much else to say. uncontaminated and
I’ve viewed it through a telescope, Mean distance from unheated material billions
and so ticked it off the list, but this the Sun: 4.5 billion km of years old. NASA’s
tiny looking ‘star’, maybe with a Rotation period: New Horizons spacecraft
hint of blue, is not as spectacular 16 hrs 6 min will reach this mysterious
as its larger compatriots. If you Orbital period: 164.8 years region in 2015.
have a very large scope it’s worth Diameter: 48,600km
catching a glimpse of Neptune’s Gravity (Earth=1): 1.14
largest moon, Triton (mag. +13.5). Mean atmospheric temperature: –225˚C
However, if I were you, I’d invest Number of moons: 13
my efforts in observing some of
the more accessible sights the
Milky Way has to offer. Through a large telescope, Neptune has a hint of blue

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