Observing from high northern latitudes in summer

Due to the extensive hours of twilight in summer, attempting to observe fainter objects such as nebulae and star clusters at night can be something of a waste of time. Moreover, even when the brighter superior planets* appear in our night skies in summer they are generally too low to make satisfactory observing subjects with high powers.

* Mercury and Venus lying inside the orbit of the Earth (closer to the Sun) are referred to as "inferior planets", those planets outside the Earth's orbit are called "superior planets" (Mars, Jupiter, Saturn for the purposes of this article). Mars, at opposition in August, will be the subject of a separate article in July.

Apart from the Moon, which is also low down in the sky, one looks to the planets Mercury and Venus for much of the interest during the summer months. June and July in 2003 will be particularly favourable for those wishing to study either planet.

Venus is seldom difficult to locate; even a small pair of binoculars will be sufficient to find the planet when it is at a safe distance from the Sun. [And here again one has to warn against the accidental observation of the Sun itself, especially with any optical device NOT specifically designed for the purpose.]

Dia. 1 : Mercury & Venus at 11h 00m GMT (UT) June 21 in a 5 degree field (average for a 8x40 binocular/small finder telescope). North is at top of diagram.

Every year Mercury becomes well disposed for observation in summer. This June 21 (the day of the summer solstice, incidentally) Mercury and Venus are in close conjunction when less than 0º.5 degree will separate them.

Mercury will be bright at magnitude -0.8 and so should be visible in the same field as Venus (see dia. 1) making it comparatively easy to observe the planet with smaller instruments (eg. 60mm refractor). Mercury will in fact be observable with modest equipment from around June 5 right through to mid August, except for a few days around superior conjunction on July 5th.

Apart from the satisfaction of finding the planet in the daytime sky very little can be detected about Mercury other than its rapidly changing phase. Telescopes of at least 200mm aperture are required in order to detect faint markings on the disc. A good refractor of 150mm aperture (and in this I include a good Maksutov reflecting telescope of slightly larger aperture) may yield something under very favourable conditions.

For those wishing to attempt Mercury and Venus on the 21st June using modest equipment, the data below will be useful:

VENUS
Transit on local meridian (Kirkwall): 11h 01.5m GMT (UT)
Altitude: 52º.6
Elongation from Sun: 16º
Phase: 96%
Visual magnitude: -3.9

MERCURY
Phase: 78.5%
Visual magnitude: -0.8

Please refer to the archive for explanation of terms and further information on Venus & Mercury.