Saturday: The
sky will be giving us a late holiday present in the form of a comet. Comet
Heinze (C/2017 T1) will pass closest to Earth on January 4. At its brightest,
it will be visible with small telescopes and 50-mm or larger binoculars. Go to https://goo.gl/2iL224 for a finder
chart.
Sunday: The
next few mornings provide a great example of how the planets move with respect
to each other and with respect to the background stars. Every morning at 7
a.m., look about two and a half fists held upright and at arm’s length above
the south-southeast horizon. This morning, Jupiter and Mars are a little less
than a half a fist from each other with the dimmer Mars to the upper right of
Jupiter. As the days go by, they move closer together with Mars “passing”
Jupiter next Saturday.
Monday: 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.
Tonight’s Full Moon is a supermoon, the biggest one of the year. That’s
because the Moon is full at nearly the same time as it is at its closest point
to Earth, called perigee. Read more about the supermoon at http://earthsky.org/?p=270121.
Tuesday: If
the Sun looks big today, your eyes are not playing tricks on you. The Earth is
at perihelion at about 9 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.
Wednesday: 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 above the northeast horizon at 1 a.m. This year, the nearly
full Moon will 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=155137.
Thursday: 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
early 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.
Friday: You’ve
heard the term “a pinch to grow an inch.” Well, Jupiter’s extremely strong
gravitational field “pinches” Jupiter so much that it causes Jupiter to shrink
by about an inch a year. Look for the svelte Jupiter two and a half fists above
the south-southeast horizon at 7 a.m. The diminutive Mars snuggles within a
pinky-width to the right of Jupiter.
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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