THE SOUTHWORTH PLANETARIUM

207-780-4249 www.usm.maine.edu/planet

70 Falmouth Street Portland, Maine 04103

43.6667° N 70.2667° W

Altitude: 10 feet below sea level

Founded January 1970
Julian Date: 2458794.16

2019-2020: XLVII

""I'm sure the universe is full of intelligent life. It's just been too intelligent to come here." -Arthur C. Clarke

THE DAILY ASTRONOMER

Wednesday, November 6, 2019
Valentine Sun

Valentine's Day

Today

The Universe will never fail to astonish us. Not only with its copious starbirth rate (20,000 per second), unfathomable extent and immense time spans. It also offers smaller surprises that still baffle and astound. For instance, did you know that the Sun's altitude now is lower than the Sun's altitude on Valentine's Day? Do you find that statement a bit difficult to believe? After all, the weather we experience in early November is, despite the deepening chill, milder than what we have to endure in February. One would think that the Valentine Sun would far lower than the one in early November.

We'll work through the details:

The sun's altitude in your sky depends on your location and the Sun's declination: its angular distance north or south of the celestial equator, the projection of Earth's equator onto the sky. The declination changes continually throughout the year as our tilted planet revolves around the Sun. When the north pole is aligned as closely to the Sun as possible on the summer solstice, the Sun attains its maximum altitude of 23.5 degrees north of the celestial equator. When the north pole is aligned away from the Sun to its maximum extent, the Sun's altitude reaches a minimum 23.5 degrees south of the celestial equator.

If we could chart the Sun's position relative to the celestial equator throughout the year, we would produce an undulating curve that is alternately "above" and "below" the celestial equator. The graphic below shows this path against the starfield. We refer to this curve as the "ecliptic," the Sun's annual path through the sky.

We can see that except for the two solstice points, the Sun will be at the same declination twice a year. For instance, the Sun's declination is precisely 0 on both the vernal and autumnal equinoxes, the first days of spring and fall, respectively. On Valentine's Day, the Sun's declination is just about -13 degrees, meaning that it will be 13 degrees south of the celestial equator. The Sun is also just about 13 degrees below the celestial equator on October 28th.

The Sun's daily path through the sky in late October is the same as that in mid February. Now that we're toward the end of November's first week, the Sun is even lower in the sky.

The Sun's declination today is -16 degrees!

Why is the average temperature now higher than that of early to mid February? Simply because November follows a protracted warm period (in theory). February follows protracted cold period. Meteorologists refer to "thermal inertia" to explain the difference between mid winter cold and mid autumn chill

So, February is colder than November even if the Sun is actually higher in the sky in early February than it is currently. Another astronomical surprise.

To subscribe or unsubscribe from the "Daily Astronomer"
http://lists.maine.edu/cgi/wa?A0=DAILY-ASTRONOMER