May 1 – 7
The moon is new on the 6th, but on the mornings
of the 2nd and 3rd, it’s visible in the low east before
sunrise. If you leave for work before sunrise, be sure to take a look at the
moon and Earthshine on its right side. You’ll need to make this observation by
around 4:45 AM. Much later and the light of dawn will wash out Earthshine.
The Eta Aquarid meteor
shower peaks on the night of the 6th and morning of the 7th,
which is awesome since this is a Friday night and Saturday morning. We can
observe up to 30 meteors per hour from this shower; unfortunately, this is the
case if you live the southern hemisphere. However, it’s still worth observing
this shower as the nights are getting warmer and the moon is new. That means
we’ll have warm, dark skies for observing this shower. There’s no need to watch
this shower all night, as the radiant for the shower doesn’t rise until after
3:00 AM. So look for meteors appearing from the low east after 3:00 AM.
May 8 – 14
The moon reappears in
the low west-northwest on the 8th. So after it gets dark after 10:00
PM, look for the moon and see if you can detect Earthshine illuminating its
dark portion. Earthshine will be most visible if you view the moon through
binoculars. The brightish orange star to the left of the moon is Betelgeuse, a
star in the shoulder of Orion. You can make observations of Earthshine for
several more nights.
Mercury made an evening appearance last month, but disappeared
before the end of April. This month Mercury passes between Earth and the sun
and in Idaho,
we get to see a part of that. This is called a transit and it only happens on
an average of 13 times per century. The transit begins on the 9th at
around 7:00 AM in Idaho
and ends shortly after noon.
A transit is not safe to observe directly with your eyes,
since it requires looking at the sun. This means that a telescope properly
covered with solar viewing filters can observe the transit of Mercury, but other
instruments cannot. The rest of us will need to rely having an acquaintance who
is an amateur astronomer, finding a local astronomy club giving public
viewings, or using the projection method of observing the sun. How can you
project an image of the sun? A pair of binoculars, spotting scope, or small
telescope pointed at the sun will project an image of the sun out its eyepiece.
Do NOT look at this image through the eyepiece. Instead, position the telescope
so that the image projecting out of the eyepiece falls upon a sheet of paper.
Then focus the binoculars, spotting scope, or telescope so that the image is
sharp. Any sunspots visible during the transit will appear to have fuzzy edges
while Mercury will be a tiny round dot with well-defined edges. Mercury will
transit south of the sun’s equator, from Earth’s perspective. Remember that if
you observe the transit with a telescope, the image will be upside down.
Gemini appears like the waist and legs of a soccer player.
Look in the low west after dark in May and you’ll see upright Gemini as two
columns of stars. At the top of the columns are two bright stars, Pollux (on
the left) and Castor (on the right). Castor and Pollux mark the head of the
Gemini Twins, but more like the waist of a soccer player. Even better, on the
evening of the 9th, the crescent moon appears at the feet of Gemini
just like Gemini is about to kick it like a soccer ball.
One of the closest stars
to the sun appears to the lower left of the moon on the 10th. The
star’s name is Procyon, which means “Before the Dog”. The dog in this case is
the Dog Star, Sirius. Procyon gets this name because it rises shortly before
the rising of Sirius. Procyon is the eighth brightest star in the sky because
it’s only 11.5 light years away and not because its particular bright compared
to other stars. Procyon is a young star, only one quarter the age of the sun.
Procyon is the brighter of the two stars forming the constellation of Canis
Minor, or the Little Dog.
Hey, want to see a really
nice star cluster? You can on almost any night, but the 11th is
better because the moon will help you find it. The star cluster is named the
Beehive Star Cluster and you’ll find it 7 degrees above the moon on the night
of the 11th. To see this attractive star cluster, point you
binoculars at the moon and then tilt them directly north of the moon. Just
after the moon leaves the binoculars’ view, the Beehive will appear at the top
of the field of view. You should see a striking similarity between the Beehive
and a swarm of bees.
The moon reaches the first quarter phase on the 13th.
The star Regulus also appears above the moon that night. Regulus is the
brightest star of Leo the Lion. The constellation is standing on end above the
moon that night. Regulus is so close to the moon that both can be seen together
at the same time through binoculars.
There’s an even brighter star above
the moon on the night of the 14th. In his case, the star is Jupiter,
the King of the solar system’s planets. Both the moon and Jupiter can be seen
together in your binoculars on the 14th. You should notice that
Jupiter appears as a more intense source of light than the moon and that it is
accompanied by a retinue of satellites. On the 14th, binoculars will
let you see up to three of Jupiter’s moons. From left to right, the moons will
be Callisto, Europa, Jupiter, and Ganymede. The planet’s innermost moon Io very
close to Jupiter and might not be visible through binoculars. If you have a
spotting scope or larger, then Io appears near the right edge of Jupiter.
May 15 – 21
The moon passes very close to Spica on the night of the 17th.
Spica is the brightest star of Virgo the Maiden, the second largest
constellation. Virgo is made up of dim stars, so the constellation doesn’t
stand out to the extent its large size should make it. One depiction of Virgo
is as a goddess of justice named Justitia. In this guise, she holds the scales
of justice in her hands, or the constellation of Libra.
A widely spaced double star located in Libra can be found below
the moon on the 19th. The star’s name is Zubenelgenubi and the
angular distance between the companion stars is wide enough that some people
can see it as two separate stars without optical aid. The rest of us need a pair
of binoculars. The star is 5 degrees below the moon, therefore, place the moon
at the top of your binocular’s view and Zubenelgenubi will be the bright pair
of stars at the bottom.
The moon is full on the 21st. Full moons in May
are sometimes called the Flower Moon and you’ll find the Flower moon located
between the planets Mars and Saturn. Mars will be the bright orange-tinted star
to the right of the moon and Saturn will be the fainter yellow-white star to
the lower left of the moon. Below the moon is another orange star, Antares.
Antares is the heart of Scorpius the Scorpion.
May 22 – 30
Mars
reaches opposition on the 22nd. At opposition, superior planets, or
those beyond Earth, are at their closest to Earth for the year. Opposition
occurs when the faster orbital motion of Earth results in Earth catching up to
and passing the superior planet in question. In the process of reaching
opposition, superior planets appear to retrograde, or move slightly backwards
across the stars. Retrograde motion is an illusion caused by the changing
perspective between Earth and superior planets when compared to the fixed
stars. Hundreds of years ago, when the geocentric or Earth-centered solar
system was in vogue, astronomers and philosophers believed the superior planets
actually moved backwards during a short period of time. This was possible
because these planets orbited Earth in a set of nested orbits of various sizes.
Copernicus convinced astronomers in the 16th century that the
retrograde motion of the planets was easier to explain by moving the sun to the
center of the solar system and demoting Earth to a planet orbiting the sun.
The bright yellowish star visible to the right of the moon
on the 22nd is Saturn. You’ll need at least a spotting scope capable
of magnifying at least 25 times in order to see the planet’s rings and largest
satellite, Titan. Titan is a fascinating world. It’s larger than Earth’s moon
and surrounded by an atmosphere denser than Earth’s. Unfortunately, it’s
intensely cold on Titan. So cold that methane, a gas used to heat our homes, is
a liquid. Its nitrogen-rich atmosphere is almost cold enough to liquefy.
Because of its dense atmosphere and liquid methane, Titan has weather, but
probably not as dynamic as Earth’s. This still allows it to rain on Titan, but
with methane rain.
If you’re a late night person, you can use the moon to
locate several star clusters and nebulae on the morning of the 24th.
These attractive deep sky objects are located between Earth and the center of
our galaxy, meaning they appear in the thick of the Milky Way (which is why you
need to wait until after midnight to see them). These clusters and nebulae are small, so
you need a pair of binoculars to see them. Through binoculars, the nebulae will
appear as fuzzy spots while the star clusters will have some stars sprinkled
among the fuzz.
The moon is last quarter
on the 29th, which is nice, but it has a neighbor that night that
will give you a real astronomy challenge. The eighth planet, Neptune is just
4.5 degrees away from the moon on the 29th. This means you can see
both together in a pair of binoculars, which typically have a field of view of
5 degrees. You need dark skies in order to see Neptune, so leave town for the
countryside. To see Neptune, place the moon on the right edge of your
binoculars and find the brightest star directly east of the moon. This star
will be near the left edge of your binoculars. A small distance farther east of
the bright star is a faint star that’s as bright as Neptune. The distance
between the star and the brighter star is the same distance Neptune is away
from the bright star. Neptune is the other faint star down and slightly left of
the bright star. The bright star, faint star, and Neptune will form a small
triangle with a 90 degree apex.
The moon is close to the eastern horizon as you drive to
work on the 31st. Can you see Earthshine? Binoculars will definitely
help (but don’t use binoculars while you drive!).
This Month’s Sources
Astronomical Phenomena of the Year 2016, The Nautical
Almanac Office and Her Majesty’s Nautical Almanac Office
Astronomy Calendar of Celestial Events for Calendar Year
2016, http://www.seasky.org/astronomy/astronomy-calender-2016.html
Climate of Titan, https://en.wikipedia.org/wiki/Climate_of_Titan
Mercury Transits the Sun,
http://skyandtelescope.com/observing/ceelstial-objects-to-watch/mercury-transits-thesun/
Night Sky Explorer
Virgo, https://en.wikipedia.org/wiki/Virgo_(constellation)
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