Leap years: proof that Earth is always running late

Unless you’ve been living under a rock, you’re probably aware 2016 is a leap year. February will have 29 days as part of a four-year mathematical cycle that has been observed in the Gregorian calendar since 1582. The reason we do this? To make up for a slight discrepancy in the Earth’s orbit around the sun.


As humans, we like to count things and measure our lives by predictable cycles, so Western cultures designed a calendar counting 365 days in a year. However, Earth’s true orbit is actually 365 days, five hours, 49 minutes and 16 seconds. That’s right; every New Year’s Eve, Earth is little under six hours late to the party. Talk about procrastination!

To make up for Earth’s tardiness, we add those six hours together every four years to make a full day. This keeps the calendar from drifting through the seasons over time. It might take a while, but if we didn’t add leap days, in 31 leap years (or 124 years), Jan. 1 would occur the first day in February. That means the Spring Equinox would happen Feb. 20 instead of in March!

But that’s not the end of the problem. In adding a day every four years, we overcompensate by 10 minutes and 44 seconds. (Remember Earth doesn’t really take another full six hours to complete its trip around the sun.) However, the Gregorian calendar accounts for this, as well.

epa04383191 A handout picture made available by NASA on 04 September 2014 shows a view of Earth taken by NASA astronaut Gregory Reid Wiseman of the US from the International Space Station (ISS) on space, 02 September 2014. The Expedition 40 crew has been busy on the ISS performing health checks and humanoid robot upgrades. A trio of orbital residents is packing up gear as they prepare to return home in less than two weeks. Commander Steve Swanson powered down and stowed Robonaut 2 after wrapping up its mobility upgrades this week. He installed new legs on the humanoid robot including external and internal gear as well as cables. This sets the stage for more upgrades in the fall before Robonaut takes its first steps as an assistant crew member. Robonaut was designed to enhance crew productivity and safety while also aiding people on Earth with physical disabilities.  EPA/NASA/REID WISEMAN  HANDOUT EDITORIAL USE ONLY

A view of Earth by NASA.

Over a period of 400 years, the true length of the leap cycle, this overcompensation amounts to a total of three days. So in every century that isn’t divisible by 400, we don’t add a leap day. The last one was back in 1900. The year 2000, divided by 400, equals five, so we did observe leap year the February after Y2K. But you’ll have to live until 2100 to notice the next time we skip it. Your kids and grandkids will probably still be around, though, likely talking about lazy Earth and the crazy math behind leap years!

When the renovated Burke Baker Planetarium opens March 11, you can see leap years in action with a full map of Earth’s orbit, as well as the rest of the planets in the Solar System. Speed up time to compare rates and see how Earth measures up. Travel to the edge of our neighborhood and meet up with Pluto and other dwarf planets, and see how astronomers found evidence of a new Planet Nine! (I wonder how long that calendar is…)

Wonder Women of STEM: Dr. Mae Jemison, the first African-American female astronaut.

Editor’s Note: This post is the fourth in a series featuring influential women from STEM (Science, Technology, Engineering and Math) fields in the lead up to HMNS’ annual GEMS (Girls Exploring Math and Science) event, February 21, 2015. Click here to get involved!


We’ve seen some amazing women in STEM, but none are quite so out of this world as Dr. Mae Jemison, the first African-American female astronaut. In 1992, she orbited the earth for over a week on the space shuttle Endeavor and logged over 190 hours in space!

Dr. Jemison had numerous accomplishments in addition to her space travel. She began her college career at age 16 by attending Stanford University on scholarship. Within 4 years, she graduated with a BS in Chemical Engineering and a BA in African and African-American Studies from Stanford University. She continued her studies at Cornell University where she received her doctorate degree in medicine. A few years later, she proceeded to volunteer for over two years with the Peace Corps in Western Africa where she taught health education and contributed to research concerning the Hepatitis B vaccination among others.

After all of her volunteer work, Jemison applied to be part of the NASA Space Program and was one of 15 people selected out of 2000 to join the Space Program in 1987. She joined her first orbiting mission in 1992 with Endeavor. While aboard Endeavor, she worked with other astronauts on bone cell research along with other experiments and investigations. Although her time in space was short, she was able to claim the title of first female African-American in space. In May of 1993, Dr. Jemison left NASA to teach at Dartmouth College and continue to educate future generations.

In addition to her space travels, Dr. Jemison has a list of accomplishments that would knock your socks off. She can speak four languages, wrote her own book called “Find Where the Wind Goes,” was on the cover of JET Magazine, hosted the World of Wonders TV show, and was voted one of the 50 Most Beautiful People according to People Magazine. If that’s not enough, she’s also got a sense of humor. She talks about her experiences in Brazil for the 20th anniversary of the Apollo missions and she comments, “Wow!! Y’all need to be glad I didn’t go to Brazil before NASA or I’d still be there doing development work and the Samba on the beach.” Like I said, impressive!

Space was not the first major accomplishment for Dr. Mae Jemison, and it certainly won’t be her last. She continues to expand interest in science education through her foundation, The Dorothy Jemison Foundation for Excellence. She created The Earth We Share, international science camp for students as well as a program to encourage hands-on, science education through Teachers.

If you are inspired by women such as Dr. Mae Jemison, then you’ll enjoy meeting some of the local ladies of STEM at GEMS this weekend. Come to HMNS between 9 a.m. and 1 p.m. to learn more about science, technology, engineering and math! We’ll even have representatives from NASA!

Go Stargazing! September Edition

Venus and Mars have left Saturn behind in the night sky (check out my earlier blog on the position of the planets). You can spot the star Spica in between Mars and Venus during this time of year. (Spica is similar to Mars in brightness and closer to Venus than to Mars). 

 Cloud structure in The Venusian atmosphere,
revealed by ultraviolet observations

September is the last full month to observe Venus at dusk. That’s because Venus has by now come around to Earth’s side of the sun on its faster, inner orbit.  Thus, Venus now begins to overtake the Earth, passing between the Earth and sun on October 29.  We’ll therefore see Venus shift farther to the left of Mars and then drop down below it.  In October, Venus exits the evening sky quite quickly as it shifts back towards the sun.  September and October 2010 is an excellent period for observing Venus’ crescent phase in telescopes.  Anytime Venus is on our side of the sun, more of its night side faces us, resulting in a crescent like appearance when magnified.

Saturn is far to the lower right of Venus and Mars as you face west at dusk.  You’ll need a horizon clear of tall buildings and trees to see it before it sets.  You’ll also need to look early in the month, as Saturn is practically behind the sun by month’s end.  

Jupiter dominates this month’s skies.  On Tuesday morning, September 21, Earth aligns with the sun and Jupiter, bringing Jupiter to opposition (because the sun and Jupiter are then on opposite sides of the Earth).  On the night of September 20-21 we see Jupiter rise at sundown and set at sunup—Jupiter is up literally all night long.  During the whole month, though, Jupiter is visible virtually the whole night.  It outshines all stars in the sky, so it’s easy to find.  Face east in late evening or south southwest at dawn to see it.  The planet Uranus is less than one degree above Jupiter this month; the two planets are closest on September 18.

The Big Dipper is setting in the northwest at dusk; you now need a horizon clear of trees and tall buildings to get a good look at it. You can extend the curve of its handle to ‘arc to Arcturus’, which is in the west at dusk tonight.  Arcturus, by the way, is the fourth brightest star we ever see at night, but the brightest one Americans ever see on a September evening.

As the Dipper gets lower, look for five stars in the shape of an ‘M’ directly across the North Star from the Big Dipper’s handle.  This is Cassiopeia, the Queen—the ‘M’ is the outline of her throne.  Her stars are about as bright as the North Star and the stars of the Big Dipper, so she’s not too hard to find. 

星空下的汗腾格里峰 / Mt. Khan Tengri under Galaxy
Creative Commons License photo credit: livepine

High overhead, look for the enormous Summer Triangle, consisting of the stars Deneb, Vega, and Altair.   This triangle was up all night long from June to early August, hence its name.  Scorpius, the Scorpion, is in the southwest at dusk.  Sagittarius, the Archer, known for its ‘teapot’ asterism, is to its left.  Between these two star patterns is the center of our Milky Way—the brightest part of that band as wee see it.  On a cloudless night far from the big city, see if you notice the Milky Way glow near the ‘teapot’ of Sagittarius. 

Look for the Great Square of Pegasus rising in the east.  The vast stretch of sky under Pegasus is largely devoid of bright stars—ancients called this the ‘Celestial Sea”. 

Moon Phases in September 2010:

Last Quarter                  September 1, 12:22 am, September 30, 10:52 pm

New Moon                       September 8, 5:29 am

1st Quarter                     September 15, 12:49 am 

Full Moon                        September 23, 4:18 am

At 10:13 pm on Wednesday, September 22, the sun is directly overhead at the equator.  As a result, everyone on earth has the same amount of daylight and the same amount of night.  That’s why it is called the equinox (‘equal night’ in Latin).  In the Northern Hemisphere, we’ve seen the days get a little shorter and the midday Sun a little lower each day since June 21.  For us, the season changes from summer to fall at the equinox.  In the Southern Hemisphere, people have seen the days lengthen and the midday Sun get a little higher each day since June.  For them, the season changes from winter to spring.

This month, see a ‘Hairy Star!’

An unexpected visitor graces our skies this month.  Comet Lulin is now visible through binoculars in late evening and morning skies.  It makes its closest approach to Earth on February 24, when it may even be dimly visible to the naked eye!

Comet Hale-Bopp
Creative Commons License photo credit: tlindenbaum

Comets are made of ice and dust and are often called ‘dirty snowballs.’ They are believed to be left over from the formation of the solar system.  As comets approach the sun, ice changes into gas and the dust embedded within the ice is released.  A cloud of particles expands out to form a coma around the comet’s solid nucleus. This coma may be a hundred thousand miles across. Radiation pressure of sunlight and the powerful solar wind sweep gases and dust off of the comet, forming tails pointing away from the Sun. The coma and tails of a comet reminded the ancient Greeks of hair; the Greek word ‘kometes’ means ‘hairy.’   

Astronomers traditionally name comets after their discoverers.  On July 11, 2007, Lin Chen-Sheng of Lulin Observatory in Nantou, Taiwan took some photographs of the sky.  The photos were part of the Lulin Sky Survey, in which astronomers search the sky for Near-Earth Objects which might pose a risk of colliding with Earth.  One of his students, Ye Quanzhi, spotted what he thought was an asteroid in three of the pictures.  Closer observation, however, revealed the coma of a comet.  Officially designated C/2007 N3, the comet was named Lulin after the observatory where it was discovered. 

Here are some interesting facts about Comet Lulin’s orbit:

The eccentricityof an orbit describes its shape.  Bound orbits are ellipses with eccentricities between 0 and 1; 0 is a perfect circle while 1 is a parabola.  Lulin has an eccentricity of 0.9999948, almost 1.  This indicates an orbit so oblong that Lulin won’t return to the inner solar system for about 50 million years.  Some sources indicate an eccentricity slightly greater than 1.  In that case, Lulin will never again approach the Sun.

Lulin was closest to the Sun (at perihelion) on January 10.  But it approached the Sun from the far side (from our perspective).  Thus, as Lulin recedes from the Sun, it approaches Earth, with closest approach on February 24.  Not to worry, though–even at its closest, Lulin will be about 150 times as far away as the Moon.

Many comets’ orbits are highly inclined to ours.  (An inclination of 0 degrees would describe an orbit in the same plane as Earth’s orbit.)  Comet Lulin has an inclination of 178.37 degrees.   This inclination of almost 180 degrees puts Lulin back in the plane of the solar system, orbiting backwards compared to the planets’ orbits. 

Since Lulin orbits almost in Earth’s orbital plane, we see not only a tail but an ‘anti-tail.’  This is dust and debris left behind as the comet moves on its path.  Lulin is now moving away from the Sun, so the dust it leaves behind seems to point towards the Sun. The true tail of a comet always points away from the Sun (and therefore, the tail leads the comet as it moves away from the Sun). 

The Hale-Bopp Comet
Creative Commons License photo credit: Wolfiewolf

Because Lulin is roughly in the plane of the solar system, traveling backwards, it appears against the same zodiac band where we find the Sun, Moon, and planets in our sky.  As I type this, Lulin is among the stars of Virgo, the Virgin, moving towards Leo, the Lion. 

As we pass more or less between the Sun and Lulin next week, we’ll see it in Leo, first near Saturn and then near the bright star Regulus.  Lulin will be rising in the east at about dusk, highest in the sky about midnight, and setting in the west just before dawn.  Since Lulin and Earth are going in opposite directions, we see Lulin move quite noticeably night to night. 

This page has some finder charts for Lulin.  Some observers have reported seeing Lulin naked-eye, at the threshold of visibility.  You must get far from city lights, therefore, to see it without binoculars or a telescope.  Remember to scan the sky for a diffuse object about half as big across as the full Moon (and much dimmer than that), not a point of light.  Those who saw the spectacular comets Hyakutake and Hale-Bopp in the ’90s should keep in mind that Lulin will be barely (if at all) be visible to the unaided eye and will not come close to their displays.  If you find Lulin, see if you can follow it as it gets dimmer but higher in the evening sky in March. 

Once it fades away, we’ll never see it again.