Sky Happenings in April, 2017


April 4, 2017
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Image courtesy of Wikimedia Commons. Source: http://www.eso.org/public/images/potw1431a/

This star map shows the Houston sky at 10 pm CDT on April 1, 9 pm CDT on April 15, and dusk on April 30.  To use the map, put the direction you are facing at the bottom.

Jupiter, near Spica in Virgo, is up virtually all night. In the west, Dazzling Orion, the Hunter sets with Taurus, the Bull.  To Orion’s left are the two Dog Stars—little dog Procyon and big dog Sirius.  Sirius outshines all other stars we see at night.  The Big Dipper is high in the north. Leo, the Lion, is high in the south. These stars, along with Arcturus, announce the spring.

The Planets This Month:

Mercury, rarely seen at night because it is so close to the Sun, makes an evening appearance in early April.  Face west at dusk and look right over the point of sunset until about April 7.

Mars remains in the west at dusk.  Mars continues to fade and get lower each night as Earth leaves it farther and farther behind.

Jupiter is up all night long this month.   April 7 is the precise date in 2017 when Earth passes between the Sun and Jupiter.  Such an alignment is called opposition because it puts the Sun and Jupiter opposite one another in our sky, causing Jupiter to rise at sunset and set at sunrise.  Face east at sundown or west at dawn to see the King of Planets.   Only the Sun, the Moon, and Venus outshine Jupiter. 

Saturn  is in the south southwest at dawn this month.

Venus enters the morning sky this month.  Look in the east at dawn.  Venus is noticeably higher above the horizon each morning, and outshines everything in the sky except the Sun and the Moon.

April is the last month to see the full set of brilliant winter stars which now fill the western evening sky.  Dazzling Orion is in the southwest at dusk.  His three-starred belt is halfway between reddish Betelgeuse and bluish Rigel.  Orion’s belt points rightward to Aldebaran in Taurus the Bull.  To Orion’s upper left are the twin stars Castor and Pollux, marking the heads of Gemini, the Twins.  You can find Sirius, the brightest star we ever see at night, by drawing a line from Orion’s belt towards the left.   Forming a triangle with Sirius and Betelgeuse is Procyon, the Little Dog Star. 

Joining the winter stars are stars of spring rising in the east.  Look for Leo, the Lion at dusk.  Ursa Major, the Great Bear, which includes the Big Dipper, is high above the North Star on spring evenings.  Extend the Big Dipper’s handle to ‘Arc to Arcturus’ and then ‘speed on to Spica’.   There are fewer bright stars in this direction because of where the plane of our galaxy is in the sky.  The area of sky between Gemini and Taurus and over Orion’s head is the galactic anticenter, which means that we face directly away from the galactic center when we look in this direction.  Those bright winter stars setting in the west are the stars in our galactic arm, right behind the Sun.  On the other hand, if you look at the sky between Ursa Major, Leo, Virgo, and Bootes, you’re looking straight up out of the galactic plane, towards the galactic pole.  There are fewer stars in this direction. 

Moon Phases in April 2017:

1st Quarter: Apr. 3, 1:39 p.m.       Full: Apr. 11, 1:08 a.m.

Last Quarter: Apr. 19, 4:56 p.m.     New: Apr. 26, 7:16 p.m.

 

Things To Look Up For:

A comet, 41P/Tuttle-Giacobini-Kresak, is in our early April skies!  This comet is one of a family of comets with aphelia (greatest distance) near Jupiter’s orbit and perihelia (closest approach) near Earth’s orbital distance.  The P means that it has a short orbital period (only 5.4 years), while Tuttle, GIacobini, and Kresak are its discoverers.  Although 41P made its closest approach to Earth on April 1, it is still approaching the Sun. Thus, the comet will keep brightening until April 12, when it starts receding from the Sun.  Right now 41P is between the Big Dipper and the North Star, in a constellation called Draco, the Dragon–a position which puts the comet in our skies all night long.  As of this date the comet is visible in binoculars but about 6 times too dim for the unaided eye.  Most don’t predict 41P will brighten enough for us to see with the unaided eye, but it’s worth observing for ourselves to see.  Some comets on approach to the Sun can have outgassing events as ice sublimates, making them suddenly much brighter, as this comet did in 1973. 

Here is a good website for more information:

https://theskylive.com/41p-info

On most clear Saturday nights at the George Observatory, you can hear me do live star tours on the observation deck with a green laser pointer.  If you’re there, listen for my announcement. 

Clear Skies!

Authored By James Wooten

James is the Planetarium Astronomer at the Houston Museum of Natural Science. He teaches students every school morning in the planetarium, and also answers astronomy questions from the public.


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