Skywatch March 2017

Skywatch March 2017

All five naked-eye planets are visible in March, and there is at least one planet visible at any time through the night. Spring starts, and the continental US goes back to daylight saving time.

A very brief goodbye to Venus

Venus begins the month in a blaze of glory, dominating the western sky in early March as it has done since November of last year. However, its days are numbered; after over five months brightening our western skies at dusk, we lose Venus as an ‘evening star’ by the middle of March.

If you look for Venus in the west on March 1, it will be significantly lower in the sky at dusk than it was only a month ago; only about 20 degrees (the width of two palms held at arm’s length) above the west horizon at 7 p.m. In early March, the planet sets a little before 8:45 p.m.

Of note on March 1 only: look for the crescent moon hanging above Venus.  In fact, there had been a young crescent moon next to Venus on the first day of every month since last November; but this March 1 is the end of this five-month special engagement, since we lose Venus entirely as an evening object long before the first of April.

Venus will be a little lower every night during the first half of March. The planet, brilliant on March 1 at minus 4.57, will also drop a little in brightness night by night, while still outshining all other sky dots. On March 10, Venus will be only ten degrees about the western horizon (the width of your palm) as it gets dark at 7:15 p.m., will shine at minus 4.41, and will be set by 8 p.m.  By March 17, it will barely appear in the west, five degrees above the west horizon at dusk, before it sets at 7:25 p.m. Soon after that, Venus will be gone; it passes right in between the sun and the earth on March 25.

Because Venus is passing between the earth and the sun on March 25, in what is called ‘inferior conjunction,’ it’s moving at a good clip from our perspective, and we’ll have it back in our sky before the end of the month, but will now be in the morning sky. Look for Venus rising in the east around 5:40 a.m. on March 31, as few minutes before first light of day.

Mercury takes up where Venus left off

Interestingly, as Venus leaves our western evening sky around St Patrick’s Day, it seems to do a tag-team handoff to the planet Mercury, which becomes visible as an evening ‘star’ right as Venus surrenders that role. On March 17, over a perfectly flat horizon such as the ocean, find Venus around 7 p.m., only five degrees (the width of two fingers) above the horizon. Then look the left of Venus; standing side by side that night with Venus is the other inner planet, Mercury, shining brightly at minus 1.35. Your viewing window is small; both planets set around 7:20 p.m.

Through the rest of March, Mercury will hang low in the west at dusk. Around the 20th, it does not emerge from the light of dusk till about 7:10 pm and sets by 7:30 p.m., so you only have 20 minutes of Mercury-hunting time; though around the 20th it shines very brightly, at minus 1.18, which will help in spotting it. By the end of March, Mercury is ten degrees above the horizon at dusk (7:15 p.m.) and does not set till 8 p.m., giving a healthy 45 minutes to view the elusive planet. By end of month the planet as faded to 0 magnitude.

While we lose Venus from the March evening sky, far-fainter Mars just keeps hanging on and on.  In early March Mars is about 1/3 of the way up in the west at dusk; by the end of the month, it’s about 1/4th of the way up at dusk. It sets at 9:30 p.m. in early March and ay 9:15 p.m. at the end.  It’s also very faint for a naked-eye planet, fading from 1.30 magnitude to 1.47 as the month goes by.

On the first of the month, Mars hangs just below the moon, while Venus shines closer down near the horizon.

Jupiter now king of the evening

Through the night hours of March 2017, there is always at least one naked-eye planet in the sky at any given time. Thus on March 1, exactly as Mars sets in the west at 9:30 p.m., Jupiter rises in the east. Jupiter is brilliant, at minus 2.5, and will be easy to spot once it clears the horizon.  In early March the planet is high in the south at 3 a.m. and is working its way down the western sky when day breaks. By the end of the month, Jupiter rises in the west at dusk, is due south at 1 a.m. and sets in the east at dawn.

On the night of March 13-14, look for the waning gibbous moon (that is, a moon that’s no longer full but not yet a half moon) next to Jupiter.

Saturn is back!

Saturn rises in the south southeast just after 2 a.m. in early March and is halfway up in the south at dawn. By the end of the month the ringed planet comes up just after midnight and is due south by dawn. The planet shines at 0.5, as bright as a good bright star, and has a distinctive yellow-white hue. Look for a big waning crescent moon next to Saturn early in the morning on March 20.

Since Saturn is not as brilliant as Venus or Jupiter, it does not pop out like those two planets do. A good guide this year is Scorpius the Scorpion, known here as Maui’s Fishhook; if you find that big bold constellation first, Saturn is to the left of the Scorpion.  Saturn is in fact about 15 degrees (the width of 1.5 palms) to the left of the bright, ruddy star Antares, the heart of the Scorpion.

Other March events

March 12: Start of Daylight Saving Time for most of continental US and Canada. As of this day, the east coast is six hours ahead of the Hawaiian Islands and the west coast is three hours ahead of Hawai‘i. The Hawaiian Islands do not observe Daylight Saving Time.

March 20: Spring begins at 6:31 p.m. Hawai‘i Standard Time on March 20 (04:31 on March 20 Universal Time).

The Southern Cross watch  

This compact Roman Cross of a constellation rises in the south southeast at midnight in early March, is due south at 2:30 a.m. and sets in the south southwest at 5 a.m.  In the  middle of March, Crux rises at 11 p.m., is due south at 1:30 a.m., and sets at 4 a.m. By the end of March, Crux rises 10 p.m. and is due south just past midnight, setting at 3 a.m. The constellation hugs the horizon during its five-hour passage above the south horizon in the islands; make sure you have a flat horizon such as the sea to view it.

It’s also good to seek the Cross around that time of the night when it’s due south; by then, the brilliant stars Alpha and Beta Centauri, to the left of the Cross, will have risen.  These two stars generally pop out far more readily than the stars in the Crux; Alpha Centauri is in fact the third brightest star in the sky, and Beta Centauri the 11th brightest. The two stars are also called ‘The Southern Pointers’; find them, go right, and they’ll point you to the Gacrux, the top star in the Southern Cross.

March Sky Map

The Big Dipper, missing from Hawaii’s evening skies every fall, is back up in the March evening sky. Our map’s time (10 p.m. in early March, 8 p.m. at the end) is a good time to spot both the Big Dipper and Cassiopeia at the same time. As the map shows, both constellations can point the way to the North Star.

While the Southern Cross won’t rise the later in the evening, our March map does show the False Cross, which rises four hours before the true South Cross. The False Cross is an asterism – a familiar star pattern than is not one of the eighty eight official constellations. It is in fact constructed from two stars of Vela the Sail, visible on our map, and two stars of Carina the Keel. Carina’s most famous star is Canopus, the second-brightest star in the sky, which is also visible on the map, low in the south.

Keah Watkins | Bishop Museum

Like all of our monthly maps, this one is good for 10 p.m. on the first day of the month, 9 p.m. for the middle of the month, and for 8 p.m. at the end.

Moon phases (Hawaiian Time zone):

First Quarter: March 5
Full: March 12
Third Quarter: March 20
New: March 28

 

2017-06-05T12:04:21+00:00 Monthly Astronomy Article|