The astronomy highlight of April 2015 is a total eclipse of the moon that occurs very early this Saturday.

That is, stay up late on Friday, and shortly after midnight, the eclipse will begin.

Lunar eclipses occur every six months. During a lunar eclipse, the Earth gets in between the sun and the moon, and blocks the sun’s light from striking the moon. In other words, Earth’s shadow falls on the moon. If the entire moon goes into the deep inner shadow of Earth (the "umbra"), we have a total lunar eclipse, and the moon turns very dark, or even "blood red."

However, many lunar eclipses are partial only; during a partial eclipse of the moon, only part of the moon goes into that dark inner shadow of Earth.

This eclipse marks the third of a series of four total lunar eclipses in a row (a "tetrad"). This is also the third and last of the total lunar eclipses in this series to be visible in Hawaii; we had great views of the ones on April 14 and Oct. 7, 2014, and will have a good view of the April 4 eclipse (weather permitting); but we will not see the next total lunar eclipse that occurs Sept 27.

The Hawaiian Islands are well-placed to get a view of this total lunar eclipse from start to finish. This eclipse starts at 12:15 a.m. Saturday, as the moon begins to enter the dark inner shadow of the Earth. More and more of the moon will appear dark, as that part of the moon moves into Earth’s umbra.

After the eclipse begins, you should start to notice a distinct change in the moon. For the next hour or so, you will see a deeper and deeper "bite" taken out of the moon as more of the moon slides into Earth’s deep inner shadow. Meanwhile the part of the moon that is not yet in the umbra will remain as bright as a regular full moon. Depending on weather conditions, the darkened part of the moon could look reddish or black.

The total phase, when the moon is completely within the dark inner shadow of Earth, starts at 1:58 a.m. and will last a mere 4 minutes and 43 seconds. This is unusual for the total phase of a lunar eclipse, which often lasts well over an hour. Indeed, the April 4 eclipse will be the shortest total lunar eclipse of the 21st century, and the shortest one since 1529.

This short duration is due to the fact that the moon barely makes it into Earth’s deep inner shadow; in both 2014 eclipses, by contrast, the moon passed through the center of the umbra. The moon nearest the "top" of the umbra (the top part of the moon seen from our point of view in the northern hemisphere) should glow unusually bright, since that part of the moon is near the edge of Earth’s dark shadow.

During the brief total phase, the stars will become much more visible than during a normal full moon, since the moon’s brightness is greatly reduced. The total phase of this lunar eclipse ends at 2:02 a.m., as the moon starts to move out of Earth’s dark shadow.

There will be another partial phase after this total phase ends, and as the moon moves slowly out of Earth’s dark inner shadow and into Earth’s fainter outer shadow. This second partial phase lasts from 2:02 to 3:44 a.m., as more of the moon returns to "normal."

Two important notes: Remember to stay up late Friday to see the eclipse start after midnight; if you stay up late Saturday to watch it, you will literally be a day late. Also, unlike the lunar eclipses of April and October 2014, Bishop Museum is not hosting a viewing party. Since the event occurs so late, and over the Easter holiday weekend, we didn’t think we’d get the strong attendance that we had for the two previous eclipse nights.

For more information, see eclipse.gsfc.nasa.gov/eclipse.html.

April planets

Throughout April, look for Venus appearing in the west about 20 minutes after sunset. Shining at minus 4 magnitude, Venus looks as bright as an airplane. As it gets dark enough to see it, Venus will be about a third of the way up in the west at dusk; the bright planet sets around 9:15 p.m. in early April, and not until 10 p.m. at the end of the month.

During April, as it gets dark enough to see Venus in the west, look high overhead for Jupiter. Jupiter shines at minus 2.5 magnitude, about five times dimmer than minus 4.0 Venus, but brighter than any other dot in the sky.

In early April, Jupiter will be about two-thirds of the way up in the eastern sky at dusk, crosses the top of the sky at 9 p.m., and sets in the west at 3:15 a.m. By the end of April, Jupiter will be high up in the west at dusk, far above Venus, and sets around 1:25 a.m.

Ever since September, the planet has emerged in the west at dusk and set by mid-evening. This run ends in late April. In early April, find Venus shining in the west at dusk, and then look down about 20 degrees (the width of two fists) for Mars, a little faint orange dot.

Early in the month, Mars sets around 8 p.m. By the end of the month Mars is lost in the light of dusk, and will not re-emerge until it appears in the morning sky in August.

Saturn is not as bright as Venus or Jupiter, but there is an easy way to find it this April. Look for the ringed planet rising in the southeast, around 10:45 p.m. in early April and 8:45 p.m. by the end. The planet shines nicely at 0.5 magnitude.

One big help in finding it this April: Saturn is in the claw of Scorpius the Scorpion all month. This famous constellation has four stars that mark off the claw of the scorpion (or the top of the fishhook if you see it as Maui’s Fishhook). Saturn is a fifth dot of light in that claw (or that fishhook-top), to the left of the others. Saturn does move against the starry background, like any planet; but since Saturn is far from the sun it moves slowly, and it will stay in its position as a fifth ‘star’ in the scorpion’s claw all month.

Mercury passes behind the sun on April 9 and then reappears as an evening "star" by April 23. Look for it low and bright in the west; around the 23rd it will emerge from the dusk around 7:15 p.m., a mere 8 degrees (4 fingers) above the horizon, will set by 8 p.m., shining at minus 1 magnitude. By the end of the month look for it emerging low in the west at dusk (7:30 p.m.), about 10 degrees above the western horizon, and setting at 8:15 p.m.

Meteor Shower

The Lyrids are the first substantial meteor shower of the year. The Lyrid meteor shower is active from April 16 to 25 and the best viewing times will be from 12:01 a.m. to dawn April 21, and from 12:01 a.m. to dawn April 22.

The Lyrids can produce up to 20 meteors an hour. On the prime viewing mornings of April 21 and 22, there will be no interference from the moon, which sets much earlier in the evening.

The Lyrids come from the debris of Comet C/1861 G Thatcher.

Mike Shanahan is director of Education, Exhibits and Planetarium. For more information, go to www.bishopmuseum.org/planetarium/planetarium.html.