Sky Diary
Find out what’s up in the night sky:
upcoming astoronomical events, interesting observations, packed with everything a stargazer needs to know
November 2017

*Observations are described for the NORTHERN hemisphere and can be made by naked eye, small binoculars or by small telescope.

Phases of the Moon
Full Moon:November 4
Last Quarter:November 10
New Moon:November 18
First Quarter:November 26
Mercury

Mercury reaches the greatest eastern elongation (22 degrees from the Sun) on November 24. This means it is east from the Sun and therefore it is observable just after the Sun's setting. However, the ecliptic is low on the western horizon in November, so that Mercury sets already around 4:45 p.m. local time. On November 20, Moon will be about 6 degrees above Mercury.

Venus

This planet can be observed in the early morning as a very bright object over the eastern horizon, but its visibility is shorter than it was in October (Venus rises later). Jupiter will be very close to Venus on November 13 morning and this should be a beautiful conjunction (close approach). On November 17 morning this pair will be accompanied by the Moon and this will be another beautiful sight.

Observation of the Moon: Basic orientation

Our Moon is relatively close to our planet Earth and some details on its surface are visible even with a naked eye. When the Moon moves across the sky, you can notice that the boundary between its illuminated and non-illuminated part moves from the right to the left. This boundary is called the TERMINATOR. When the Moon is exactly between the Earth and Sun, we do not see it - we speak about the New Moon. Then, the MORNING terminator starts to move from the right to the left, i.e. the Sun RISES on the Moon's surface exactly on the morning terminator. If you were standing on the Moon's surface exactly on the morning terminator, the Sun would rise for you naturally on your EASTERN horizon (this is the definition of LOCAL EAST on any planet or moon). However, if you stand on the Earth's surface and look towards the Moon, then you see its illuminated part to the right, i.e. to the LOCAL WEST on the Earth. Hence, the right boundary of the Moon is towards Moon's LOCAL EAST, and its left boundary is towards its LOCAL WEST. So, please, remember: local East and West on the Moon are towards Earth's local West and East, respectively, i.e. they are INTERCHANGED with respect to the Earth. There is no problem with the Moon's local North and South, which are towards the top and bottom of the Moon's disk, respectively.

When the morning terminator halves the Moon's disk, we have the First Quarter. Approximately after another 7 days the morning terminator reaches the left boundary of Moon's disk (i.e. the Moon's west) and we have the Full Moon. Then, on the right (locally eastern) Moon's boundary, the EVENING terminator appears and moves again from the right (Moon's east) to the left (Moon's west). If you were standing on the Moon's surface on the evening terminator, you would see the Sun SETTING DOWN on your local western horizon (this is the natural definition of the local west). When the evening terminator halves the Moon's disk, we speak about the Last Quarter. Then, after another 7 days, the evening terminator reaches the left (Moon's western) boundary of the Moon's disk, the Moon is exactly between the Earth and Sun, and we have again the New Moon.

Please notice that the full cycle of the Moon's phases takes about 29 full days (i.e. 29 x 24 hours) as measured on Earth. For a given, fixed place on the Moon, approximately one half of this time (14.5 full days on Earth) the Sun is over the local horizon (= one "day" on the Moon), and another half of this time (14.5 full days on Earth) the Sun is under the local horizon (= one "night" on Moon).

This never-ending play between the darkness and light, the Moon's day and night, is the easiest observation on the Moon that can be made by naked eye.

Article by (C) Gabriel Okša

Read Older (October 2017)
October 2017

*Observations are described for the NORTHERN hemisphere and can be made by naked eye, small binoculars or by small telescope.

Venus

Similarly to September, this planet can be observed in the early morning as a very bright object over the eastern horizon. The Moon will be very close to Venus in the morning on October 18.

Moon and Aldebaran

Aldebaran is the brightest star ("alpha") in the constellation of Taurus (the Bull). Its beautiful orange color is the sign of its rather cold "surface" (photosphere), from which the photons reach our eyes. It is a giant star with the diameter 44-times larger than our Sun, and its distance is about 65 light-years from our planet. The Moon approaches Aldebaran on October 9 morning, high in the southern sky, and will be about 0.6 degree north from it. This event can be best observed with naked eye or small binoculars, so that both objects can be viewed together.

Article by (C) Gabriel Okša

Read Older (September 2017)
September 2017

*Observations are described for the NORTHERN hemisphere and can be made by naked eye, small binoculars or by small telescope.

Mercury

Mercury reaches the greatest west elongation (18 degrees from the Sun) on September 12. This means that it is west from the Sun, hence observable in the early morning twilight. Mercury meets the Moon on September 19/20 (i.e. the night from Sept. 19 to Sept. 20); the Moon will be south from Mercury and very close to the planet.

Venus

This planet can be observed in the early morning as a very bright object over the eastern horizon. The Moon will be very close to Venus on September 17/18.

Saturn

This planet is observable in the evening around 9:00 p.m. local time in the southern sky, quite low over horizon. You can see it by naked eye, but it is necessary to know its actual position among the stars. Using binoculars, you can see its yellow disk. To see its beautiful rings, you will need a small telescope with, say, 60 mm objective lens, the magnification around 70x and a sturdy tripod. The rings are wide open and we see them from the northern side.

Article by (C) Gabriel Okša