New Nova in the "Teapot," Algol Blinks, and Uranus Occults a Star

  

 From - Sky & Telescope

 By- Bob King

 Edited by - Amal Udawatta

The nova is located between the Teapot's "Spout" and the bright open cluster M7 in Scorpius. I include a suggested star-hopping route, starting at the 2nd magnitude star Epsilon (ε) Sagittarii. Once you've arrived at the asterism (circled), use the chart below to pinpoint the nova's location. North is up.
Stellarium with additions by Bob King

A new nova for early risers plus three fun observing 

projects for the week ahead.

We have a new "star" in the night sky. In truth, it's been there for billions of years, but it only first revealed itself a little more than a week ago. Nova Sagittarii 2025 no. 3 was independently discovered on March 23–24 by the Russian New Milky Way (NMW) Survey and Japanese amateur Tadashi Kojima at a right ascension of 18h 02′ and declination of –33° 11′. Both parties caught the star around magnitude 13; two days later it had brightened to 10.5. Despite its southerly declination, the nova stands more than 10° above the horizon before the start of dawn, making it an attainable target even for observers in the northern U.S.

It's a quick hop to the nova from the circled asterism. Take a close look at the star's color — many novae glow red from hydrogen emission during the early phase of the explosion. V7993 Sgr has also been reported to have a red color. Decimals are omitted in the comparison star magnitudes. For example, 106 equals magnitude 10.6.
Courtesy of the AAVSO

Clouds have thwarted my attempts to see it, but most estimates posted to the AAVSO peg it at magnitude 10.7 on April 1st. Not long after its discovery, the star received the official designation V7993 Sagittarii, making it the 7,993rd variable star to be discovered in Sagittarius. Although novae can appear anywhere in the sky, they're far more common within the star-dense band of the Milky Way, and especially in Sagittarius where we face toward the galactic center. In fact, this is the third nova discovered so far this year in the constellation.

This animation depicts an outburst of the recurrent nova T CrB but also demonstrates the nova eruption process. Watch until the end for the exciting conclusion.
NASA's Goddard Space Flight Center Conceptual Image Lab

In last week's post, I described novae, recurrent novae, and dwarf novae. All three types occur in close binary star systems, in which one member is a hot, dense white dwarf and the other a normal star. In each case, material flows from the companion into a flattened cloud of hot gas called an accretion disk, which spins around the dwarf. In a nova, material funnels down from the disk to the star's surface until sufficient mass has accumulated for heat and pressure to ignite the gas in a runaway thermonuclear explosion. The blast creates a brilliant fireball, which slowly cools and fades. A recent measurement clocked V7993's expanding debris cloud at 700 kilometers a second (1.6 million mph). Despite the blast, the white dwarf remains intact after the blast, and the process begins anew.

Novae generally skyrocket in brightness quickly, then gradually fade over the following weeks and months. Watching a nova dim (and occasionally re-brighten!) makes them great long-term observing subjects. Use the AAVSO map and comparison stars to help you follow V7993 Sgr's variations.

Demon Star in eclipse

Algol is a binary star consisting of a B8 main sequence star (blue) and a larger, cooler K0 subgiant. Every 2.9 days, the subgiant eclipses the hotter star. A minor, secondary dip in the system's light occurs when the B star passes in front of the subgiant. The red-black dot tracks the light variations.
Merikanto, CC BY-SA 4.0

As a budding 11-year-old amateur astronomer, Algol in Perseus was my first variable star. I still remind myself to gaze its direction every clear night I'm out from fall through spring. Every 2.9 days the more massive but fainter star in this binary system eclipses the smaller, brighter companion. In full eclipse at minimum light, Algol shines weakly at magnitude 3.4 compared to its usual 2.1. The difference is very apparent with the naked eye.

If you've read about Algol and have never observed it (or it's been a while), you'll have the opportunity to see it in eclipse on the night of April 3rd. At 10:11 p.m. EDT that evening, the star will dim to minimum light. For one hour on either side of minimum, it remains near that brightness. But if you check 2 hours or more after minimum, you'll see it begin to recover in brightness.

Use the comparison stars, labeled with magnitudes, to track changes in the variable's light as it rises from or falls to minimum.
Stellarium with additions by Bob King

Despite eclipses occurring at short intervals, they're visible only infrequently for any particular location. After the April 3rd event, the next widely and easily visible eclipse takes place on April 26th. For more eclipse times and additional information, visit Sky & Telescope's Minima of Algol calculator.