National Astronomical Observatory of Japan



The sky of Tokyo, Calendar, Planets (April, 2017)

The sky of Tokyo

The sky of Tokyo (8:00 p.m. Mid-April)
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Calendar (April)

1Greatest Eastern Elongation of Mercury / Occultation of Aldebaran
4First Quarter Moon
6Saturn at stationary point
8Jupiter at opposition
10Mercury at stationary point
11Full Moon
13Venus at stationary point
14Uranus at conjunction
19Last Quarter Moon
20Mercury at inferior conjunction
22Lyrid Meteor Shower peaks around this time(The best visibility is before dawn on the 23nd. About 5 meteors per hour are expected. Because there is no moonlight and the timing of the maximum is good, conditions are good.)
26New Moon
29Showa Day [Showa-no-hi] (national holiday)
30Venus at Greatest Brillancy

The days for the peak activities of the meteor showers are based on the predictions of IMO(International Meteor Organization).


Mercury reaches its greatest eastern elongation on the 1st. It can be seen low in the western sky after sunset in the beginning of the month. Until the 7th, its elevation as seen from Tokyo exceeds 10 degrees at 30 minutes after sunset, making it easy to see. From the middle to the end of the month, its position is close to the Sun, making observation difficult. Mercury reaches inferior conjunction on the 20th, after that it is positioned low in the eastern sky before sunrise. From the 1st to the 7th, its brightness is -0.1 to -1.1 magnitude.
Venus shines brightly low in the eastern sky just before sunrise. At the beginning of the month, its elevation is low, making it difficult to find. But its elevation increases at the end of the month, making it easy to find. Its brightness is -4.2 to -4.5 magnitude. Venus reaches its greatest brilliancy on the 30th.
At the beginning of the month, Mars is located in the constellation Aries and moves east. In the middle of the month, it moves into the constellation Taurus. It can be seen low in the western sky after sunset. Mars sets before 21:00 as seen from Tokyo. Its brightness is 1.5 to 1.6 magnitude.
Located in the constellation Virgo, Jupiter rises in the eastern sky around sunset. It reaches opposition on April 8. This is a good time to observe Jupiter. Its brightness is -2.5 to -2.4 magnitude.
Located in the constellation Sagittarius, Saturn rises in the southeastern sky around midnight at the beginning of the month and around 22:00 at the end of the month as seen from Tokyo. It reaches its stationary point on the 6th; before that Saturn moves slowly to the east (direct motion), after passing the stationary point, it moves to the west (retrograde motion). At the stationary point, it seems to stop with respect to the stars. Its brightness is 0.4 to 0.3 magnitude.

Source: Ephemeris Computation Office, NAOJ

With the “Sky Viewer” you can easily explore the appearance of a typical urban night sky (planets and constellations are visible). The Celestial Phenomena section of the glossary explains the planetary phenomena terms: greatest elongation, opposition, conjunction, stationary, etc.