Saturday: If
the Sun looks big today, your eyes are not playing tricks on you. The Earth is
at perihelion at about 3 p.m., Pacific Standard Time. If you dig out your Greek
language textbook, you’ll see that peri- means “in close proximity” and helios
means “Sun”. So, perihelion is when an object is closest to the Sun in its
orbit, about 1.5 million miles closer than its average distance of 93 million
miles. Since it is winter in the Northern Hemisphere now, the seasonal
temperature changes must not be caused by the Earth getting farther from and
closer to the Sun. Otherwise, we’d have summer when the Earth is closest to the
Sun. The seasons are caused by the angle of the sunlight hitting the Earth. In
the winter, sunlight hits the Earth at a very low angle, an angle far from
perpendicular or straight up and down. This means that a given “bundle” of
sunlight is spread out over a large area and does not warm the surface as much
as the same bundle in the summer. For the Northern Hemisphere, that very low
angle occurs in December, January and February.
Sunday: Late
tonight and early morning’s weather forecast: showers. Meteor showers, that is.
The Quadrantid meteor shower peaks late tonight and early tomorrow morning
between midnight and dawn. Meteor showers are named after the constellation
from which the meteors appear to originate. That makes this shower mysterious
because there isn’t any constellation with this name now. The shower was named
after Quadrans Muralis, an obsolete constellation found in some early 19th
century star atlases. These meteors appear to come from a point in the modern
constellation Draco the dragon. This point is about three fists held upright
and at arm’s length above the northeast horizon at 1 a.m. This year, the waning
crescent moon will not obscure the dimmer meteors. Meteors are tiny rocks that
hit the Earth and burn up in the atmosphere. Most meteors are associated with
the path of a comet. This shower consists of the debris from an asteroid
discovered in 2003. Keeping with the comet-origin paradigm, astronomers think
the asteroid is actually an “extinct” comet, a comet that lost all of its ice
as it passed by the Sun during its many orbits. For more information about the Quadrantid
meteor shower, go to http://earthsky.org/?p=4287.
Monday: Jupiter
is a half a fist above due east at 11 p.m.
Tuesday: On
these cold mornings, it is difficult to get going. You just want to plop into a
chair and sit still. But, are you really sitting still? You’re moving at about
700 miles per hour due to the rotation of the Earth on its axis and 66,000
miles per hour due to the revolution of the Earth around the Sun. If that’s not
enough, the entire solar system is orbiting the center of the galaxy at a
whopping 480,000 miles per hour! So while you may be sitting still with respect
to your living room (and all of the over achievers in your house), you are NOT
sitting still with respect to the center of the galaxy. For more information
about this concept, go to http://goo.gl/lPVPS. Before
you barf from all of that motion, go outside at 7 a.m. and observe five Solar
System objects. Bright Venus is one and a half fists above the southeast
horizon. Saturn is about a half a fist to the lower left of Venus. Mars is
three fists above due south. Jupiter is three and a half fists above the
southwest horizon. And, of course, I bet you spotted the moon while you were
finding the other objects. Speaking of motion, because of Saturn’s rapid
rotation, only 10.5 hours, it appears visible flattened.
Wednesday:
Has it been tough to wake up this past week? It should have been because the
sunrise has been getting a little later since summer started. I know. I know.
December 21 was the shortest day of the year. But, because the Earth’s orbit
around the Sun is elliptical and not circular, the Earth does not travel at a
constant speed. It moves faster when it is closer to the Sun and slower when it
is farther away. This leads to the latest sunrise occurring around the first of
January and the earliest sunset occurring in early December, not on the first
day of winter, the shortest day of the year. On the first day of winter,
however, the interval between sunrise and sunset is the shortest. For more
information, go to http://goo.gl/SJC5r.
Thursday: A
new year leads us to contemplate our future. Let’s take some time to contemplate
the Sun’s future. The Sun has spent a few billion years as a stable star fusing
hydrogen into helium. Once that easily fusible hydrogen is gone, the Sun’s
outer layer will puff up like a hot air balloon, getting larger, cooler, and
redder. The star Aldebaran, in the constellation Taurus looks like what our Sun
will look like in a few billion years. Read more about Aldebaran and the Sun’s
future at https://stardate.org/radio/program/moon-and-aldebaran-25. At 9:30
p.m., Aldebaran is almost exactly 60 degrees, or six fists, above due south.
Friday:
Have you ever looked down on the ground and spotted a penny? In Yakima? While
you were standing in Ellensburg? If you have, then you may be able to see the
star Hamal as more than just a point of light. It has an angular diameter that
can be directly measured from Earth. Hamal, the brightest star in the
constellation Aries the ram, has the same angular diameter as a penny 37 miles
away. (For comparison, the moon is about half the diameter of a penny held at
arm’s length.) Hamal is three and a half fists above due west at 11 p.m.
The
positional information in this column about stars and planets is typically
accurate for the entire week. For up to date information about the night sky,
go to http://nightsky.jpl.nasa.gov/planner.cfm.
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