Saturday: All of the naked eye planets are visible tonight. First, look low in the southwestern sky at 5:00 p.m. Venus is the bright point of light a half a fist held upright and at arm’s length above the southwestern horizon. Mercury is to the lower right of Venus and much dimmer. At this same time, Saturn is about two fists above the south-southwestern horizon, Jupiter is about four fists above the southern horizon, and Mars is about three fists above the eastern horizon.
Sunday: Today is the day we celebrate the anniversary of
something new – a new classification of celestial objects. Giuseppe Piazzi
discovered Ceres [pronounced sear’-ease], the first of what are now called
“asteroids”, on January 1, 1801. Ceres is the largest asteroid in the belt
between Mars and Jupiter. At first, Piazzi thought it was a star that didn’t
show up on his charts. But, he noted its position changed with respect to the
background stars from night to night. This indicated to him that it had to be
orbiting the Sun. The International Astronomical Union promoted Ceres to the
status of “dwarf planet” in August of 2006.
Monday: Regulus, the brightest star in the constellation Leo
the lion is one and a half fists above due east at 10:00 p.m.
Tuesday: 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
northeastern horizon at 1:00 a.m. This year, the Moon will be nearly full so
the dimmer meteors will be lost in the lunar light pollution. However, this is
still one of the four major meteor showers with a sharp peak, meaning that
you’re still guaranteed to see many more meteors than on a typical night if you
are patient.
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=155137.
Wednesday: If the Sun looks big today and tomorrow, your
eyes are not playing tricks on you. The Earth is at perihelion at 8:17 a.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.
Thursday: Now that you know meteors are rocks that burn up
in the atmosphere, you will soon start to wonder what would happen if those
rocks hit the surface of the Earth. Well, wonder no more. The browser-based app
called Asteroid Launcher will simulate the collisions. You select the asteroid
type, size, speed, and angle of impact. The most common impactor material is
stone and the typical speed is 40,000 miles per hour, in case you want to
introduce some realism into your simulation. Go to https://neal.fun/asteroid-launcher/,
click on the map where you want the asteroid to land and then launch your
virtual asteroid.
Friday: 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 in late December/early January and the earliest sunset
occurring in early December. Neither of these happen on the first day of
winter. On the first day of winter, however, the interval between sunrise and
sunset is the shortest, making it the shortest day of the year. For more
information, go to http://goo.gl/SJC5r.
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 https://nightsky.jpl.nasa.gov/planner.cfm.
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