Conjunction
A conjunction is an alignment of objects at the same
celestial longitude. The conjunction of the Moon and
the planets is determined with reference to the Sun.
A planet is in conjunction with the Sun when it and
Earth are aligned on opposite sides of the Sun.Opposition
When a celestial body is in line with the Earth and
Sun. During opposition, an object is visible for the
whole night, rising at sunset and setting at sunrise. At
this point in its orbit, the celestial object is closest to
Earth, making it appear bigger and brighter.Declination (Dec)
This tells you how high an object will rise in the sky.
Like Earth’s latitude, Dec measures north and south.
It’s measured in degrees, arcminutes and arcseconds.
There are 60 arcseconds in an arcminute and there
are 60 arcminutes in a degree.
Magnitude
An object’s magnitude tells you how bright it
appears from Earth. In astronomy, magnitudes are
represented on a numbered scale. The lower the
number, the brighter the object. So, a magnitude of
-1 is brighter than an object with a magnitude of +2.Right Ascension (RA)
Right Ascension is to the sky what longitude is to
the surface of the Earth, corresponding to east and
west directions. It is measured in hours, minutes and
seconds since, as the Earth rotates on its axis, we see
different parts of the sky throughout the night.Greatest elongation
When the inner planets, Mercury and Venus, are at
their maximum distance from the Sun. During greatest
elongation, the inner planets can be observed as
evening stars at greatest eastern elongations and as
morning stars during western elongations.Jargon buster
Globular cluster
Messier 2 is well
placed for observation
in Aquarius15
AUG
Asteroid 39 Laetitia
is well placed for
observation in
Capricornus17
AUG
Comet 260P/
McNaught makes its
closest approach to the
Sun in the dawn sky10
SEP
The alpha-Cygnids will
reach their peak of five
meteors per hour21
AUG
Conjunction between
the Moon and Jupiter
in Ophiuchus6
SEP
The Moon and Jupiter
make a close approach,
passing within 2°15’ of
each other in Ophiuchus6
SEP
The Moon and Saturn
make a close approach,
passing within 0°02’ of
each other in Sagittarius8
SEP
Conjunction between
the Moon and Saturn
in Sagittarius8
SEP
The Moon and Pluto
make a close approach,
passing within 0°03’ of
each other in Sagittarius9
SEP
Naked eye
Binoculars
Small telescope
Medium telescope
Large telescope
© ESA/Hubble & NASASTARGAZER
What’s in the sky?
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