Eastern Dawn Sky in June 2019

This chart is intended for skywatchers who want to find the Matariki/Pleiades star cluster in the dawn sky. 

This year the brilliant planet Venus crosses the region around the same time that Matariki becomes visible.  The cluster is first seen by eye in the dawn around June 14 each year.  By chance Venus happens to be to the right of Matariki around the date of first visibility. 

The position of Venus on June 15 is shown by the large filled circle.  The planet’s position five days before and at five-day intervals afterwards is shown by the open circles. 

The Matariki/Pleiades/Subaru cluster is quite faint.  So even in a dark sky it has to be well above the eastern horizon before it is visible.  It is also easily hidden by twilight and artificial light.  Together the need for some elevation and not too much twilight mean the cluster is hidden till mid-June. 

As the Earth moves around the Sun the Sun appears to move against the background stars. We can’t see the stars in daytime so this isn’t obvious.  What we see is the stars being a little further west each night.  Because of the tilt of the Earth’s axis the Sun’s track is tilted.  At this time of year the Sun is well north of the equator.  Astronomers call the Sun’s track the ecliptic.  That’s because the Moon has to be on this track and either near the Sun in the sky, or opposite the Sun in the sky for a solar or lunar eclipse to occur. 

The cluster is also north of the equator and not far from the ecliptic.  So the cluster disappears from the evening sky around March as the Sun moves toward it from the west, from below in our evening sky view. It remains hidden through April and May as the Sun passes it by.  Then it reappears in the dawn as the Sun moves east of the cluster, or downward and away in our dawn-sky view.   This happens regardless of where one is in the world because the Sun’s track passes near the cluster. 

Alan Gilmore                                                                                                                         27 May 2019

For more information, visit the Royal Astronomical Society of New Zealand’s website where Peter Jacquiery has added to the event’s description.

Visibility of Puaka and Matariki

Alan Gilmore, the former superintendent of the University of Canterbury Mount John Observatory at Tekapo, explains the difference between the reappearance of Puaka and the rising of Matariki each winter.

The Earth circles the Sun through the year. This causes the Sun to appear to move a little east against the background stars each day. We take our time from the Sun, not from the stars, so we see the stars shifting a little west each day. This causes the stars to rise and set four minutes earlier each day. That is why we see different stars at different times of the year.

Most people know the pattern of ‘The Pot’ or ‘The Saucepan’, Orion’s belt and sword in European and Middle Eastern astronomy. The Pot is first seen in the evening sky in spring when it is rising in the east. By summer it is midway up our northern sky at dusk. (Puaka/Rigel, a bright bluish star, is then straight above The Pot.) In the autumn The Pot falls lower in the western sky. Around the beginning of June it can be seen both setting in the dusk and rising in the dawn. So it never completely disappears from our sky. The three bright stars of The Pot are on the equator of the sky.

Stars in the south stay in our sky all the time. The Southern Cross is nearly overhead on May and June evenings. In August and September it is nearly on its side on the southwest. In November it is upside down low on the south skyline. In February–March it is on its other side in the southeast sky.

The Earth’s axis is tilted to its orbit. That is why we have seasons. In our summer the southern hemisphere is tilted towards the Sun. In our winter, when the Earth is around the other side of the Sun, the southern hemisphere is tilted away from the Sun. Between the summer and winter the Earth’s equator is pointed at the Sun. That’s when we have the equinoxes: equal day and night.

The Earth’s tilt causes the Sun’s annual track through the stars to be tilted to the equator of the sky. In our summer the Sun hides star patterns of the southern sky around the Scorpion and Sagittarius. As the Sun moves on these constellations appear in the dawn sky. They are overhead in mid-winter.

The Matariki/Pleiades star cluster is in the north sky close to the Sun’s track. So Matariki is hidden by the Sun from late April to mid-June as the Sun moves past that part of the sky.

The Sun’s track is well north of, or below, Orion. So Puaka is never hidden by the Sun from our southern hemisphere viewpoint. At the end of May and for most of June Puaka can be seen both setting in the western sky at dusk and rising in the eastern sky at dawn.

Matariki, being a cluster of stars much fainter than Puaka, is not seen in bright twilight nor when it is near the horizon. It has to be higher in a darker sky to be seen. There are no reliable naked-eye sightings of Matariki before June 14.

Approximate rise times for Puaka/Rigel, the Sun and Matariki at Dunedin (a.m. NZST)
Date           Puaka/Rigel       Sun        Matariki
May 20          7:20                 7:50
May 25          7:00                 7:55
May 30          6:40                 8:00
June 4            6:21                 8:05            7:14
June 9            6:01                 8:08            6:55
June 14          5:41                 8:11            6:35
June 19          5:22                 8:13            6:15